Hydrogen doi: 10.3390/hydrogen7020067

Authors: Yulong Jiang Zhifu Wang Jian Li Zhonghao Heng

High-temperature gaseous deuterium charging was used to investigate hydrogen isotope permeation, retention, microstructural stability, and fracture response in 310S austenitic stainless steel. Gas-driven permeation, thermal desorption spectroscopy, two-dimensional diffusion simulation, XRD/EBSD characterization, tensile testing, and fractographic analysis were combined to correlate isotope transport with mechanical and fracture behavior. The deuterium permeability and diffusion coefficient followed an Arrhenius relationship, and the diffusion coefficient extrapolated at 673 K was 1.11 × 10−11 m2/s. With increasing charging time, the deuterium distribution evolved from a surface-enriched unsaturated state to an overall near-saturated state with higher retention. Although deuterium charging had little influence on yield strength, ultimate tensile strength, and elongation under the present room-temperature tensile condition, local quasi-cleavage-like facets, secondary cracks, and serrated fracture edges became more evident after charging. These results indicate that the embrittlement response of 310S stainless steel was mainly characterized by localized hydrogen-assisted damage rather than dominant brittle fracture.

Hydrogen doi: 10.3390/hydrogen7020066

Authors: Jianhua Yang Fangyi Han Wenbin Cheng Yaqiang Yang Chaoming Shen Fushan Li Meiliang Zhong

High-pressure gaseous hydrogen storage is widely adopted in the hydrogen energy industry chain due to its simplicity, reliability, and economic viability. However, when these systems are subjected to rapid filling, a series of complex thermodynamic behaviors are induced. These have been identified as a bottleneck restricting the safety and service life of hydrogen storage and transportation equipment. In this paper, a detailed review is conducted on the recent domestic and international research progress regarding the thermodynamic issues encountered during the charging process of storage devices. Research achievements related to the thermodynamics of the process are systematically classified, summarized and discussed. These achievements are analyzed from four aspects: thermodynamic theoretical models, numerical simulation analysis, experimental testing, and thermal management strategies. The thermodynamic mechanism of the charging process is revealed, and the variation laws of thermodynamic responses during charging are sorted out. Key factors affecting the thermodynamic behaviors of charging are clarified, and the implementation effects of different thermal management strategies are elaborated. Finally, based on the future development trend and prominent potential challenges in high-pressure hydrogen storage, the future development directions of the thermodynamics of hydrogen fueling in storage and transportation devices are explored and prospected.

Hydrogen doi: 10.3390/hydrogen7020065

Authors: Guohui Song Xiang Wang Haiming Gu Sheng Wang Jingxin Xu Cai Liang Hao Zhao Lirong Wang

The use of differential pressure energy for green hydrogen and ammonia comes with significant safety challenges. Two zero-emission technical schemes—one based on magnetic coupling transmission and another based on dual magnetic fluid seals—were proposed and designed. The energy performance of both schemes was first analyzed for a DN200 pipe using the DWSIM software (Version 8.6.6). Subsequently, the levelized cost of electricity and the dynamic payback period were evaluated and compared. The results show that the magnetic coupling transmission scheme exhibits relatively low energy efficiency (54.9–61.7%), whereas the scheme based on dual magnetic fluid seals is more complex yet achieves higher energy efficiency (65.8–67.1%). The levelized electricity cost of both schemes under a differential pressure of 0.5 MPa is estimated to be lower than the feed-in tariff of coal-fired power plants in China, and the dynamic payback period is estimated to be less than 5.5 years. Overall, both schemes provide benefits in energy savings and profitability. These schemes warrant further experimental investigation and pilot testing.

Hydrogen doi: 10.3390/hydrogen7020064

Authors: Ryosuke Shinkai Takashi Tomita

Pressure ulcers are chronic wounds characterized by repeated ischemia–reperfusion injury, persistent inflammation, and redox imbalance, in which excessive production of reactive oxygen species (ROS) contributes to delayed healing. Thus, debridement is an essential therapeutic procedure for removing necrotic tissue and biofilm, thereby reconstructing the wound microenvironment. Recent experimental studies suggest that molecular hydrogen may improve wound healing through attenuation of oxidative stress and modulation of inflammatory responses, while debridement represents a dynamic intervention phase in which redox imbalance may transiently develop. Here, we propose the hypothesis that the use of hydrogen-enriched saline as an irrigation solution during hydrosurgical debridement may attenuate excessive redox imbalance and stabilize the wound microenvironment during this dynamic intervention phase. Such intra-procedural modulation may facilitate the transition from inflammation to the proliferative phase of wound healing, thereby promoting tissue repair. This approach is expected to attenuate the transient oxidative burst following debridement, as reflected by reductions in redox-related biomarkers in the wound environment, including ROS levels and oxidative damage markers such as 8-hydroxy-2′-deoxyguanosine and lipid peroxidation products, with relative decreases in these biomarkers compared with conventional debridement, potentially consistent with reductions observed in preclinical oxidative stress models. These findings are consistent with findings from previous experimental studies demonstrating attenuation of oxidative stress markers following hydrogen administration. This hypothesis introduces a novel therapeutic concept, redox modulation during the debridement process, offering a practical strategy for integrating hydrogen-based therapy into existing wound management without altering current surgical techniques.

Hydrogen doi: 10.3390/hydrogen7020063

Authors: Olga Morozova Olga Kudryashova

The reaction of aluminum with water is a promising method for producing hydrogen on demand for autonomous energy systems. However, its practical implementation faces the challenge of process control due to high exothermicity, leading to particle sintering and thermal instability, especially when using highly reactive nanopowders. The goal of this study is to implement an integrated approach to controlling this reaction, aimed at minimizing these risks. The approach is based on the principle of spatial and temporal distribution of reactants to ensure uniform heat release. Two process management methods were investigated: electrostatic application of aluminum powder to the reactor walls with its gradual release and pre-treatment of a nanopowder-ice mixture. Using a macrokinetic mathematical model, calculations of the conversion kinetics and heat release were performed and compared with experimental data. The results showed that both methods prevent slurry self-heating and achieve uniform hydrogen generation at a constant rate. In particular, the use of a pre-frozen mixture ensured stable hydrogen production over a long period of time without additional heating or stirring. The proposed approaches can be used in the design of safe and efficient hydrogen generators for autonomous power plants.

Hydrogen doi: 10.3390/hydrogen7020062

Authors: Borislav Abrashev Valentin Terziev Tony Spassov

The main goal of this study was to develop and validate a laboratory-scale prototype of a rechargeable metal hydride (MH)–air battery integrating gas diffusion electrodes (GDEs) and MH electrodes with stable performance over extended operation (>500 h) and repeated charge–discharge cycling (>100 cycles). This work addresses the critical transition from optimized electrode materials to a functioning system by investigating its operation under deep-discharge conditions, a key but still insufficiently explored regime in the context of stationary renewable energy storage. In this respect, this study explicitly targets the practical applicability of the developed system rather than focusing solely on material-level performance. The most efficient electrode materials, previously optimized, were successfully integrated into a single-cell configuration and systematically evaluated under various operating conditions. By determining the limiting current density for stable GDE operation, an appropriate operating window was defined, enabling maximum capacity utilization without compromising electrode integrity. At a current density of 10 mA, the maximum depth of discharge was achieved at a cell voltage of 575 mV, ensuring operation in a regime that limits GDE degradation while maintaining high energy efficiency. In addition, the electrode retains its mechanical stability after operation is interrupted, indicating good structural robustness. Furthermore, the performance of two identical cells connected in series was investigated to assess system scalability. The cells were operated under near-limit conditions and exhibited stable behavior. Overall, the present results confirm that the developed MH–air battery system extends beyond laboratory-scale validation and shows strong potential for implementation in stationary energy storage applications.

Hydrogen doi: 10.3390/hydrogen7020061

Authors: Rocio Maceiras Victor Alfonsin Miguel A. Alvarez-Feijoo Jorge Feijoo Adrian Lopez-Granados

Decarbonizing maritime transport requires hydrogen storage technologies that are efficient, safe, and compatible with fuel cell systems. This study evaluates three hydrogen storage technologies (compressed hydrogen (CH2), liquid hydrogen (LH2), and metal hydrides (MH)) based on five key criteria: safety, autonomy, environmental impact, cost, and implementation feasibility. Applying two multi-criteria decision-making (MCDM) methods, Analytic Hierarchy Process (AHP) and Technique for Order Preference by Similarity to Ideal Solution (TOPSIS), the alternatives are systematically ranked to identify the most suitable option. Both methods consistently highlight compressed hydrogen as the most viable storage solution, offering a good balance of safety, infrastructure maturity, and economic performance. Liquid hydrogen, despite its superior autonomy, is limited by high energy and infrastructure costs. Metal hydrides, although safer and more compact in terms of volumetric density, are limited by low gravimetric efficiency at the system level due to the additional weight of the storage material and associated components.

Hydrogen doi: 10.3390/hydrogen7020060

Authors: Xuejun Zhou Jianliang Zhang Yaozu Wang Ben Feng Shaofeng Lu Zhengjian Liu

In the context of global carbon neutrality goals, substituting hydrogen for carbon as a reductant represents a critical pathway for mitigating emissions in the iron and steel industry. Hydrogen-based molten reduction technology, characterized by its rapid reaction kinetics and high feedstock flexibility, has emerged as a pivotal direction for the industry’s low-carbon transition. This article systematically reviews research progress on the hydrogen-based reduction of molten iron oxides. The thermodynamic behavior of molten systems is discussed, confirming the feasibility of reducing molten FeO with hydrogen at elevated temperatures. Furthermore, discrepancies and nonlinear characteristics within current mainstream thermodynamic databases regarding the high-temperature molten region are identified. Kinetic studies demonstrate that reduction rates in the molten state significantly exceed those in the solid state. The rate-limiting step is shown to vary with reaction conditions, primarily shifting between interfacial chemical reaction and liquid-phase mass transfer control. Additionally, the influence mechanisms of key parameters—including temperature, reaction time, gas flow rate, gas composition, and slag composition—on the reduction process are comprehensively reviewed. By synthesizing existing methodologies and theoretical advancements, this review aims to provide a theoretical reference for optimizing hydrogen-based molten reduction processes for iron oxides.

Hydrogen doi: 10.3390/hydrogen7020059

Authors: Maroš Križan Ivan Červeňanský Roman Zavada

Large-scale and long-term hydrogen storage is one of the main obstacles to the wider use of hydrogen as a possible substitute for natural gas. A solution could be depleted natural gas fields, which have proven capacity and are already geologically prospected. However, part of this field remains occupied by residual natural gas, meaning that hydrogen is mixed with natural gas during storage and purification after extraction is therefore necessary. The aim of this study was to design and evaluate a hydrogen purification process for separating hydrogen from natural gas after extraction from a depleted natural gas field while maintaining the required hydrogen purity and recovery. Input data provided by Nafta a.s. were used for the mathematical simulation of hydrogen separation throughout a 150-day extraction period. A mathematical model of membrane separation and pressure swing adsorption (PSA) was developed. A single membrane stage was only able to operate effectively during the first 50 days of withdrawal while maintaining at least 80% hydrogen recovery. A two-stage membrane configuration achieved hydrogen purity above 98% with final recoveries above 80–85%, while the hybrid membrane–PSA system enabled hydrogen purity of 99.8% and total recovery of 82.5% on the last day of extraction.

Hydrogen doi: 10.3390/hydrogen7020058

Authors: Ivelina Tsacheva Mehmet Suha Yazici Cenk Turutoglu Gergana Raikova Konstantin Petrov Dzhamal Uzun

The production of green hydrogen via aqueous electrolysis of hydrogen sulfide (H2S) holds significant potential to address challenges related to sustainable energy generation and environmental protection. The electrocatalytic splitting of water polluted with highly toxic H2S is attractive for industrial applications because the process: (i) is less power-consuming than direct thermal H2S decomposition; (ii) achieves high Faradaic efficiencies for hydrogen production; and (iii) yields elemental sulfur as an added-value by-product. This review covers a brief discussion on sulfide-containing water sources and electrochemical methods for hydrogen production from H2S, specifically Direct, Indirect, and Electrochemical Membrane Reactor (EMR) systems. To become commercially and economically attractive, these approaches require improvements in electrolysis efficiency through the development of low-cost electrode materials that are resistant to sulfur poisoning and corrosion, while possessing high catalytic activity, enhanced stability, and durability. Early research focused on carbon-based materials combined with noble metal oxides, transition metal compounds, and related materials. Since their practical performance is limited, investigations have shifted toward nanostructured electrocatalysts with unique crystal structures and designs, which show significantly improved efficiency for H2S electrolysis. This review highlights the potential of H2S electrolysis for hydrogen production, giving special attention to recent advancements in electrode materials.

Hydrogen doi: 10.3390/hydrogen7020057

Authors: Diego Israel Rivas-López Manuel Alejandro Beltrán-Zúñiga Jorge Luis González-Velázquez Gabriel Sepúlveda-Cervantes Héctor Javier Dorantes-Rosales Darío Alberto Sigala-García Suset Santana-Hernández

An empirical model of the kinetics of Hydrogen-Induced Cracking (HIC) in API 5L steels was derived using the best-fit equation for experimental data obtained from cathodic charging tests. The model represents the growth of both individual and interconnecting cracks, using a double exponential equation known as the Gumbel distribution. Current density was the main independent input variable, as it is related to the hydrogen influx during the cathodic charging experiment. The results indicated that in the initial hours of cathodic charging most of the available HIC nucleation sites are activated, the growth of these individual cracks being the main contribution to the overall kinetics. Further crack growth is due to the interconnection of individual cracks, decreasing the growth rate until it becomes nearly zero. The proposed model is used in a simulation algorithm that accurately describes the complete HIC kinetics, for both short- and long-term hydrogen charging exposure, reproducing the effects of applied current density on the total cracked area and growth rates. Finally, the simulation algorithm adequately predicts the spatial distribution of HIC in a bidimensional plane that emulates the detection of HIC by C-scan ultrasonic inspection.

Hydrogen doi: 10.3390/hydrogen7020056

Authors: Shuzhi Zhang Vansh Sharma Venkat Raman

Hydrogen-enriched fuel injection in staged gas-turbine combustors is commonly achieved through jet-in-crossflow (JICF) configurations, where flame stabilization is governed by a local balance between flow-induced strain/mixing and chemical reaction rates. This work investigates turbulent reacting JICF relevant to staged combustion conditions using high-fidelity simulations with adaptive mesh refinement (AMR) and differential-diffusion effects together with Lagrangian particle statistics. Chemistry model uncertainties are incorporated by using a projection method that maps uncertainty estimates from detailed mechanisms into the model used in this work. Results show that the macroscopic flame topology remains in a stable two-branch regime (lee-stabilized and lifted) and is primarily controlled by the jet momentum–flux ratio J. Visualization of the normalized scalar dissipation rate reveals that the flame front resides on the low-dissipation side of intense mixing layers, occupying an intermediate region between over-strained and under-mixed regions. While hydrogen content does not significantly change the global stabilization mode for the cases studied, uncertainty analysis reveals composition-dependent differences that are not apparent in the mean behavior alone. In particular, visualization in Eulerian (χ, T) state-space analysis and particle statistics conditioned on the stoichiometric surface demonstrate that higher-hydrogen cases observe a lower scalar dissipation rate and exhibit substantially reduced variability in OH production under kinetic-parameter perturbations, whereas lower-hydrogen blends experience higher dissipation and amplified chemical sensitivity. These findings highlight that, even in globally similar JICF regimes, the hydrogen content can modify the local response of the flame to kinetic-parameter uncertainty, motivating uncertainty-aware interpretation and design for hydrogen-fueled staging systems.

Hydrogen doi: 10.3390/hydrogen7020055

Authors: Sergio Martínez-Vargas José-Enrique Flores-Chan Humberto-Julián Mandujano-Ramírez Salatiel Pérez-Montejo Damián Calan-Canche Cristobal Patino-Carachure

Hydrogen (H2) was produced from recycled aluminum microparticles (180–250, 300–425, and 425–500 μm) via alkaline hydrolysis using a 1.0 M NaOH solution to enhance oxide layer removal and aluminum dissolution. Maximum hydrogen flow rates of approximately 13, 15, and 19 mL·min−1 were obtained, confirming that smaller particle sizes promote faster reaction rates due to increased specific surface area. The hydrogen evolution exhibited two-stage kinetic behavior: an initial stage characterized by rapid aluminum dissolution and increasing H2 production, followed by a gradual decline associated with the formation of a passivating Al(OH)3 layer. Despite the higher reaction rates observed for smaller particles, the maximum cumulative hydrogen production was obtained for the intermediate particle size (363 µm, 132 mL), compared to 106 mL and 102 mL for 215 µm and 463 µm, respectively, indicating a trade-off between surface area and passivation effects. Kinetic analysis based on the shrinking core model showed excellent agreement (R2 = 99.94–99.97%), with rate constants of 0.137, 0.064, and 0.050 min−1. The relationship k ∝ d−n (n ≈ 1.4) suggests a mixed kinetic regime involving both surface reaction and diffusion through the Al(OH)3 layer. These findings indicate that hydrogen generation can be modulated by particle size; however, the relatively low flow rates and yields limit its immediate practical applicability.

Hydrogen doi: 10.3390/hydrogen7020054

Authors: Chao Fu Zeyu Chen Hanqing Liu Long Ma Yuwei Sun

Hydrogen is a clean energy carrier with broad application potential. This study focuses on improving hydrogen production efficiency in a proton exchange membrane (PEM) electrolyzer system that integrates a photovoltaic (PV) array, a battery energy storage system, and the electrolyzer. The PV array is interfaced with the electrolyzer through a buck converter using a maximum power point tracking (MPPT) algorithm to ensure maximum energy harvesting. A key contribution of this work is the integration of a battery system through a dual-active-bridge (DAB) converter. The DAB converter employs a multilayer perceptron (MLP) model to dynamically regulate the electrolyzer current and maintain optimal operating efficiency. An adaptive energy management strategy is further proposed to address solar irradiance fluctuations and enhance long-term operational stability. The MLP model is developed in Python and embedded into a PLECS simulation environment. The simulation results verify the effectiveness of the proposed control approach and efficiency optimization scheme. Throughout the simulation period, the PEM electrolyzer sustains an optimal efficiency of 69.9% under maximum PV power output. A limitation of this study is that the efficiency model is derived from the literature and does not yet consider all operational factors, indicating the need for refinement in future work.

Hydrogen doi: 10.3390/hydrogen7020053

Authors: Konstantin Gomonov Svetlana Ratner Arsen A. Petrosyan Svetlana Revinova

The development of a green hydrogen industry is a strategic priority for Russia’s energy transition, yet the dynamics of scaling up this nascent sector remain poorly understood. This study uses agent-based modeling (ABM) to simulate the co-evolution of Russia’s electricity, hydrogen, and electrolyzer sectors over 2024–2050. The model incorporates three types of heterogeneous agents (power producers, hydrogen producers, and electrolyzer manufacturers) operating under bounded rationality. Four scenarios are examined across 50 Monte Carlo runs each, varying the electrolyzer learning rate (10–25%), willingness to pay for green hydrogen (2–6 $/kg), and government support intensity. The results reveal an endogenous three-phase development pattern: Phase I (2024–2028) dominated by renewable capacity build-up reaching ~30 GW; Phase II (2029–2040) characterized by rapid electrolyzer deployment scaling to 14.5 GW; and Phase III (2041–2050) marked by stabilization at approximately 30 GW producing 1.12 Mt/year at 3.1 $/kg. Two critical thresholds are identified: renewable capacity exceeding 30–38 GW and low-cost electricity above 4–7 TWh/year. The electrolyzer learning rate emerges as the most influential parameter, while the pessimistic scenario confirms market failure without a green premium (WTP < 2 $/kg). Strategic investment losses of 2–6 billion USD are necessary catalysts for industry emergence. Russia’s 2030 production target (0.55 Mt) is found structurally infeasible under all scenarios.

Hydrogen doi: 10.3390/hydrogen7020052

Authors: Francisco Alejandro Jiménez-Becerra Francisco Oviedo-Tolentino Marcos Loredo-Tovías Raúl Ignacio Hernández-Molinar Juan Carlos Arellano-González

One of the main challenges in hydrogen production via electrolysis is the reliable measurement of the electrical work supplied. In this work, a robust electronic data acquisition system was developed to obtain precise and accurate data to evaluate the electrical work. The electrolytic concentration and electrical work were the main variables in this study. The supplied electrical energy was analyzed under both constant and pulsed voltage conditions. The results reveal that hydrogen production depends on voltage amplitude, PWM, and electrolyte concentration. The applied voltage shows a slight positive correlation with hydrogen production. PWM influences hydrogen production in the range of 0 to 1 Hz, while no significant effect is observed at higher frequencies. Electrolyte concentration has a stronger influence on hydrogen production in the range of 0.125 to 0.25 M. The optimal operating conditions were identified at 0.375 M, 1 Hz and 6 VDC, and under these conditions the hydrogen production is 0.145 mL/s and the specific energy is 165 kWh/kg.

Hydrogen doi: 10.3390/hydrogen7020051

Authors: Ifeanyi Oramulu Vincent P. Paglioni

The rally to mitigate growing carbon emissions and climate change necessitates decarbonization strategies, with hydrogen emerging as a key candidate option across multiple sectors. This review examines the current state of the hydrogen economy, including production, implementation, and associated risks. Hydrogen’s versatility in industry, transportation, and energy storage is highlighted, alongside the challenges of transitioning from fossil fuel-based production. It explores the current state of hydrogen technologies, differentiating between green, blue, and gray hydrogen production methods, and highlights advancements in production techniques like thermochemical water splitting. Key findings show that while green hydrogen offers the cleanest pathway, high production costs and infrastructure limitations remain significant barriers to widespread adoption. This study also addresses safety concerns and public perception, emphasizing the need for robust risk assessment methodologies and management approaches. Furthermore, this paper underscores the importance of technological innovations, such as high-temperature electrolysis and synergies with renewable energy sources, to enhance efficiency and sustainability. Policy recommendations include financial incentives, regulatory frameworks, and international cooperation to accelerate hydrogen adoption and balance its development with other low-carbon solutions.

Hydrogen doi: 10.3390/hydrogen7020050

Authors: José Luis Iturbe García Elizabeth Teresita Romero Guzmán

Research on hydrogen production by chemical methods has focused on combining metals to carry out the hydrolysis reaction under ambient conditions. In particular, aluminum and lithium metals were considered, with lithium used at low concentrations in order to activate aluminum. Under these conditions, the metals can react with water to obtain the maximum hydrogen yield. The main objective of this work was to prepare the lithium−aluminum alloy by mechanical milling and its chemical reaction with water to produce hydrogen under laboratory conditions. A high–energy Spex mill was used for material preparation and the time scheduled for alloys preparation was relatively short. Several techniques were used for its characterization, such as X–ray diffraction, scanning electron microscopy, gas chromatography, and low-temperature physical adsorption. According to the results, two phases were produced during the milling process when using 5% lithium. The volume of hydrogen generated was measured using a graduated burette. Depending on the volume obtained, the aluminum reacted to generate hydrogen with an efficiency of 95.24%. No additives or catalysts were used in material synthesis or hydrogen production. According to these results, the hydrogen does not require any purification because it is clean hydrogen and can therefore be used directly in fuel cells.

Hydrogen doi: 10.3390/hydrogen7020049

Authors: Adamu Kimayim Gaduwang Bassam Tawabini Nasiru S. Muhammed

The decarbonization of hard-to-abate sectors remains a significant challenge in achieving net-zero emissions targets. These industries depend on energy-dense fuels, making direct electrification and the direct use of hydrogen technically and economically challenging. Electrofuels present a promising pathway to reducing emissions while leveraging surplus renewable energy. This review evaluates the feasibility of electrofuels for deep decarbonization, focusing on production processes, energy demands, and economic viability. Environmental performance is discussed in terms of lifecycle greenhouse gas (GHG) emissions, carbon circularity considerations, and energy conversion efficiencies, while techno-economic feasibility is evaluated using metrics such as levelized cost of hydrogen (LCOH), CO2 capture costs, and projected fuel production costs. The review indicates that while electrofuels can achieve substantial lifecycle emission reductions up to 40–90%, depending on pathway and electricity source, their deployment remains constrained by high energy demand, conversion losses, and capital costs. Projected reductions in LCOH to below $2.1/kg by 2030 and declining renewable electricity costs could significantly improve competitiveness, particularly in regions with abundant solar and wind resources. However, substantial trade-offs exist between efficiency, infrastructure compatibility, scalability, and carbon neutrality across different electrofuel routes. The review identifies key technological bottlenecks, cost drivers, and research priorities necessary to position electrofuels as a strategic solution for deep decarbonization in sectors where direct electrification is not feasible.

Hydrogen doi: 10.3390/hydrogen7020048

Authors: Mboneni Charity Mbengwa Emmanuel Kweinor Tetteh Sudesh Rathilal

This study compares hydrogen production pathways from water—using renewable-powered electrolysis (alkaline, water-based)—and biomass (gasification), under harmonized system boundaries and a common functional unit of 1 kg H2 at 99.97% purity. It examines technological efficiency and environmental impacts, including cradle-to-gate Life Cycle Assessments (LCAs) of each pathway, focusing on global warming potential (GWP100), water consumption, land use, acidification, cumulative energy demand, and the critical minerals footprint. The analysis highlights the roles of water electrolysis and biomass gasification within South Africa’s energy landscape, considering the integration of renewable electricity, energy quality, and co-product allocation. Economic factors, such as the Levelized Cost of Hydrogen (LCOH), are evaluated alongside environmental indicators. The study emphasises the environmental challenges of biomass gasification, notably water use and emissions, and contrasts these with the climate benefits of renewable-powered electrolysis. It also reviews policy initiatives and government programs that support hydrogen and sustainable energy in South Africa, aligning with the SDGs. Overall, the findings underscore the trade-offs in hydrogen development, emphasising opportunities for resource utilisation while addressing deployment challenges.

Hydrogen doi: 10.3390/hydrogen7020047

Authors: Zhiyang Yao Chunjuan Huang Zhongwei Wang

Despite the long-standing recognition of nickel as an effective electrocatalyst for the alkaline hydrogen evolution reaction (HER), the majority of extant studies primarily focus on initial catalytic performance or short-term stability under relatively low current densities. In practical alkaline water electrolysis, however, electrodes operate continuously at elevated current densities for extended periods, where surface chemical states and electrochemical responses may evolve dynamically. A systematic understanding of such time-dependent behaviour remains limited, particularly for electrodeposited nickel under sustained operation. In this study, the long-term HER performance of electrodeposited Ni electrodes at a current density of 100 mA cm−2 over 120 h is investigated. The objective of this study is to correlate the evolution of electrochemical performance with changes in surface chemical states during prolonged electrolysis. To this end, a combination of methods was employed, including polarization measurements, electrochemical impedance analysis, double-layer capacitance evaluation, and ex situ surface characterization. In contrast to the tendency to prioritize absolute enhancement of activity, this study places greater emphasis on the transient decline–recovery–stabilization behaviour that is observed during operation. Furthermore, it discusses the potential relationship of this behaviour with surface hydroxylation and restructuring processes. The present study utilizes a time-resolved analysis to elucidate the dynamic surface evolution of nickel electrodes under practical alkaline HER conditions, thereby underscoring the significance of evaluating catalyst durability beyond the confines of short-term measurements. The findings presented herein contribute to a more realistic assessment of nickel-based electrodes for alkaline water electrolysis applications.

Hydrogen doi: 10.3390/hydrogen7020046

Authors: Batuhan Senol Josef Meiers Georg Frey

The global energy transition demands solutions that balance intermittent renewable energy generation while decarbonizing heat and power sectors. Hydrogen has appeared as a versatile energy carrier, enabling sector coupling across electricity, heat, and industry. This work explores the integration of hydrogen into combined heat and power (CHP) systems, with a regional focus on Saarland, Germany. It depicts H2-ready technologies including combustion engines, gas turbines, and fuel cells, and introduces a custom Python-based (Version 3.13) techno-economic optimization model to simulate multi-energy system operations. The analysis reveals that high hydrogen costs, electricity price volatility, and market design significantly constrain economic viability. However, Saarland’s industrial structure and cross-border infrastructure projects offer strategic opportunities for scalable hydrogen deployment. The article concludes with targeted recommendations for technology development, policy reform, and regional replication, positioning hydrogen CHP as a flexible and decarbonizing solution in energy-intensive regions.

Hydrogen doi: 10.3390/hydrogen7020045

Authors: Amani Alremeithi Ammar Alkhalidi Mahmoud Fayyad

Countries are increasingly adopting hydrogen, leading to growing interest in developing sustainable hydrogen supply chains. Ports, being essential nodes in supply chains, must be prepared to facilitate hydrogen exports. However, there is a shortage of thorough port readiness studies for hydrogen exports. Existing research remains fragmented or confined to individual case studies, offering no transferable framework. This study fills this gap by creating a framework that covers four essential aspects of port readiness for exporting hydrogen: infrastructure, safety, legal, and management. The ports of the United Arab Emirates served as a case study, and the Delphi method was used to validate and contextualize the proposed framework. This study demonstrates the framework’s capacity to identify deficiencies in port readiness across multiple dimensions, helping stakeholders to plan and make decisions more easily.

Hydrogen doi: 10.3390/hydrogen7020044

Authors: Chrisale Ngueloheu Yeda Thomas Jeannin Aurélien Neveu David Chapelle Anne Maynadier

In a solid-state hydrogen storage tank, the storage medium is most often in the form of an intermetallic alloy powder. With each cycle of hydrogen absorption/desorption, the particles swell, move, fragment, and segregate. Understanding and modeling these phenomena are essential in order to guide engineers during the tank design process. However, there are little data in the literature on the mechanical behavior of powders for storage applications. This study focuses on the flowability and compression behavior of an intermetallic powder, with the aim of analyzing particle mobility in a confined environment as well as the transmission of forces to the tank walls. In order to represent the evolution of particle size through fragmentation during cycles, five TiFe1−xMnxx≈0.1 powders, differing in their average particle size and polydispersity, are studied. Flowability tests on Granutools® (Awans, Belgium) instruments show that behaviors differ. Fine-grained samples exhibit rheo-thickening behavior, while coarser samples are quasi-Newtonian. These tests highlight variations in cohesion and internal friction, particularly for polydisperse samples. Stepwise cyclic compression tests (in stages 0-10-20-30 kN) were performed to study the elastic response of the powder under confinement and its ability to transfer stresses to the walls. This work highlights the impact of particle size and polydispersity on stress transfer in a confined space. This work therefore presents the mechanical effects of changes in particle size and polydispersity during absorption/desorption cycles on the overall behavior of the powder storage bed, in terms of flowability, cohesion, and stress transmission, in order to better understand, in the long term, its impact on tank deformation.

Hydrogen doi: 10.3390/hydrogen7010043

Authors: Sana Kordoghli Abdelhakim Settar Oumayma Belaati Mohammad Alkhatib Khaled Chetehouna Zakaria Mansouri

This work contributes to advancing sustainable energy and waste management strategies by investigating the thermochemical conversion of food-based biomass through pyrolysis, highlighting the role of artificial intelligence (AI) in enhancing process modelling accuracy and optimization efficiency. The main objective is to explore the potential of underutilized biomass resources like spent coffee grounds (SCGs) and DSs (date seeds) for sustainable hydrogen production. Specifically, it aims to optimize the pyrolysis process while evaluating the performance of these resources both individually and as blends. Proximate, ultimate, fibre, TGA/DTG, kinetic, thermodynamic, and Py-Micro-GC analyses were conducted for pure DS, SCG, and blends (75% DS-25% SCG, 50%DS-50%SCG, 25%DS–75%SCG). Blend 3 offered superior hydrogen yield potential but had the highest activation energy (Ea: 313.24 kJ/mol), while Blend 1 exhibited the best activation energy value (Ea: 161.75 kJ/mol). The kinetic modelling based on isoconversional methods (KAS, FWO, and Friedman) identified KAS as the most accurate. These approaches work together to provide a detailed understanding of the pyrolysis process with a particular emphasis on the integration of artificial intelligence (AI). An LSTM model trained with lignocellulosic data predicted TGA curves with exceptional accuracy (R2: 0.9996–0.9998).

Hydrogen doi: 10.3390/hydrogen7010042

Authors: Yuhan Guo Menglong Zhao Yan Yi Jiahao Cao Bingyan Wang Hong Zhang Wenfang Cai Kai Cui Sunil A. Patil Kun Guo

Hydrogen-mediated microbial electrosynthesis (MES) of chemicals from CO2 relies on effective gas–liquid transfer at the cathode interface, yet the extent to which cathode surface area regulates acetate productivity remains insufficiently quantified. In this study, three identical MES reactors equipped with stainless-steel cathodes of different geometric areas (8 × 1, 8 × 4, and 8 × 16 cm2) were operated at a constant electric current of 0.3 A. The largest cathode significantly accelerated hydrogen mass transfer (kLa = 0.592 h−1), reaching dissolution equilibrium within 3 min, which was nearly twice as fast as the smallest electrode. Upon inoculation with enriched acetate-producing microbial consortia, the 8 × 16 cm2cathode reactor fed with CO2 achieved the highest steady-state acetate concentration of 32 g·L−1 produced at a rate of 2.12 g·L−1·d−1, with 94% hydrogen utilization, and 59% coulombic efficiency. In contrast, smaller electrodes exhibited rapid bubble detachment and reduced residence time, thereby limiting microbial gas uptake, and resulting in low acetate productivity. These findings demonstrate that cathode surface area is a key engineering lever controlling both hydrogen availability and electron recovery efficiency in H2-driven MES. The results provide practical guidance for electrode design and scale-up of CO2-to-acetate bioconversion via the MES process.

Hydrogen doi: 10.3390/hydrogen7010041

Authors: Enric Palau Forte Francesc Medina Cabello

External leakage from valve stem packings is a critical safety and reliability issue in high-pressure hydrogen systems. This work aims to quantify how packing geometry and polymer selection influence stem sealing in a PN650 needle valve (316L body and stem). Two geometries were compared: a conical V-ring (chevron style) stack and a flat three-disc stack. Two polymer material sets were assessed: Vespel® polyimide (SP-1/SP-21) and a glass-filled PTFE sealing element combined with a virgin PEEK back-up ring. Four assemblies (one per geometry/material combination) were first screened by hydrostatic pressure hold testing up to 1500 bar and by helium mass spectrometer leak measurements under vacuum. All assemblies sustained the hydrostatic overpressure hold with negligible decay. Vacuum helium screening produced leak rates between 3.7 × 10−10 and 9.5 × 10−10 mbar·l·s−1, with the conical V-ring geometry consistently outperforming the disc stack. A more demanding helium test at 700 bar with external vacuum yielded leak rates of 3.6–3.7 × 10−8 mbar·l·s−1, for conical assemblies. Based on the screening results and practical industrial considerations, the PTFE/PEEK conical configuration was selected for endurance testing and completed 2500 open/close cycles in 650 bar hydrogen without gland readjustment. Post-cycling checks confirmed continued tightness, including a qualitative helium pressure hold result near 700 bar and 0 bubbles in 10 min in the seat tightness test. Microscopy/EDX revealed limited wear with minor metallic transfer. The proposed multi-stage workflow provides a pragmatic route for the early qualification of stem packings for high-pressure hydrogen valves.

Hydrogen doi: 10.3390/hydrogen7010040

Authors: Ayoub Koufi Younes Ziat Hamza Belkhanchi Noureddine Elmeskini

In this study, density functional theory (DFT) within the generalized gradient approximation (GGA) is employed to investigate the structural, electronic, mechanical, and thermoelectric properties of perovskite hydrides XZrH3 (X = Mg, Ca, Sr, Ba). Mechanical stability and ductility are evaluated through the Cauchy pressure, Pugh’s ratio, and Poisson’s ratio, all of which point to ductile behavior with a dominant ionic-bonding character. Electronic structure calculations reveal metallic behavior arising from band overlap at the Fermi level. Equilibrium energy–volume data are fitted with the Murnaghan equation of state, and transport coefficients are extracted using the BoltzTraP package as implemented in WIEN2k. The absence of a band gap and the overlap between valence and conduction bands confirm conductor-like behavior. Lattice thermal conductivity for MgZrH3, CaZrH3, SrZrH3, and BaZrH3 increases monotonically with temperature. Overall, the results identify MgZrH3 in particular as a promising candidate for thermoelectric devices and solid-state hydrogen storage, thereby supporting progress toward a sustainable hydrogen economy.

Hydrogen doi: 10.3390/hydrogen7010039

Authors: Changchang Yang Chunhuan Luo Qingquan Su

CO-selective methanation (CO-SMET) is an important technology for CO deep removal from reforming hydrogen. We previously proposed a three-stage CO-SMET with a decreasing temperature profile based on critical CO concentration. In this study, focusing on the sharp decline in each stage’s CO inlet concentration, we further proposed and validated a three-stage CO-SMET process characterized by an increasing space velocity profile, combined with a decreasing temperature profile. Compared to operating all stages at an identical space velocity of 9000 h−1, increasing the space velocities of the second and third stages to 27,000 h−1—thereby raising the overall space velocity from 3000 h−1 to 5400 h−1—only modestly increased the CO outlet concentration from 2.1 ppm to 6.5 ppm, while slightly improving the CO selectivity from 75.3% to 76.3%. These findings offer valuable insights into CO-SMET design that simultaneously achieve high CO-removal depth, high CO selectivity, and high space velocity.

Hydrogen doi: 10.3390/hydrogen7010038

Authors: Fiyinfoluwa Joan Medaiyese Maryam Nasiri Ghiri Hamid Reza Nasriani Leila Khajenoori Khalid Khan

The conversion of plastic waste into hydrogen offers a promising waste-to-value pathway, but its industrial viability is constrained by high external energy demand associated with thermochemical processing. This study evaluates the energy performance of hydrogen production from mixed plastic waste via pyrolysis and in-line steam reforming, with a focus on reducing utility consumption through systematic heat integration. A steady-state process model was developed in Aspen Plus for a representative mixture of polyethylene, polypropylene, and polystyrene, followed by detailed energy analysis and pinch-based heat integration using Aspen Energy Analyser. Baseline utility requirements were quantified and compared against optimised configurations incorporating targeted heat exchanger network modifications. The base-case analysis identified significant recoverable heat, enabling a reduction in total external utilities from 7.14 to 2.88 GJ h−1, corresponding to a 59.6% decrease in utility demand. Sequential heat integration scenarios further reduced heating and cooling duties while maintaining process operability, demonstrating the effectiveness of iterative, pinch-guided design. The results show that high-temperature waste-plastic-to-hydrogen systems need not be utility-dominated when energy integration is embedded at the design stage. These findings highlight heat integration as a critical enabler for improving the energy efficiency and sustainability of pyrolysis–reforming routes and provide a robust framework for developing scalable, low-carbon hydrogen production from plastic waste.

Hydrogen doi: 10.3390/hydrogen7010037

Authors: Dk Nur Hayati Amali Pg Haji Omar Ali Hazwani Suhaimi Pg Emeroylariffion Abas

Ammonia decomposition is one of the most used pathways for carbon-free hydrogen production, particularly in systems where ammonia is used as a hydrogen carrier. Modelling and simulation are critical for the general quantification of reaction kinetics, transport limitations, reactor performance, and system-level integration; however, simulation-based studies remain disjointed across modelling scales and synthesis routes. This systematic review examines modelling and simulation studies on ammonia decomposition published in the period between 2014 and 2025, identified through a structured Scopus search and screened using PRISMA methodology. A total of 70 modelling-focused studies were classified into five modelling categories: reactor-scale numerical and CFD modelling; kinetic and thermochemical mechanism modelling; thermodynamic, energy, and exergy-based process simulation; multiscale or cross-scale modelling; and conceptual or dimensionless modelling frameworks. The results show that reactor-scale CFD and kinetic models constitute most published studies, while integrated multiscale frameworks linking catalyst-scale phenomena to reactor and process-level performance remain limited. Furthermore, the inclusion of techno-economic analysis (TEA) and life-cycle assessment (LCA) is limited, restricting quantitative evaluation of scalability and system viability. Based on the reviewed literature, key methodological gaps are identified, and a multiscale modelling roadmap is proposed to support the design, optimisation, and scale-up of ammonia-to-hydrogen conversion systems.

Hydrogen doi: 10.3390/hydrogen7010036

Authors: Nikolaos Diamantakis Nikolaos Xynopoulos Jil Sheth John Andresen Mercedes Maroto-Valer

The maritime shipping industry faces the challenge of decarbonising its operations while maintaining economic viability. We present a comprehensive techno-economic review of four alternative energy carriers, liquid hydrogen (LH2), ammonia (NH3), liquefied natural gas (LNG), and methanol, evaluating their suitability for maritime applications within the context of global decarbonisation policy. Through the comparative assessment of physicochemical properties, hazard profiles, storage requirements, and regulatory compliance mechanisms, this review demonstrates that fuel selection is highly route-dependent, with methanol emerging as the most practical near-term solution for short-sea corridors, ammonia emerging as the primary pathway for long-term deep-sea decarbonisation, leveraging existing production infrastructure to achieve up to 90% lifecycle GHG reduction when produced from renewable hydrogen, and hydrogen serving as an alternative option pending cryogenic infrastructure maturation. The integration of digital twin technologies and port call optimisation provides a realistic pathway to achieving International Maritime Organisation (IMO) decarbonisation targets by 2030 and beyond. The findings are contextualised within current and emerging regulatory frameworks, including MARPOL Annex VI and FuelEU Maritime, to support evidence-based fuel selection and infrastructure investment decisions.

Hydrogen doi: 10.3390/hydrogen7010035

Authors: Ashleigh Cousins Nikolai Kinaev Sandy Edwards Matt Langley Evan MacA. Gray

Currently, H2 compression is one of the highest-cost items, both in terms of capital and operating costs, at H2 refuelling stations. Metal hydride (MH) compressors are an alternative H2 compression technology, which uses heat rather than electricity to provide the driving force for compression. Where waste heat is available, these compressors have the potential to be lower in cost than current mechanical alternatives. While the development of metal hydride compressors has been underway for the last 40–50 years, only a few have made it through to demonstration at industrial sites. To better understand where these compressors see best potential, we have completed a high-level assessment of the levelised costs associated with MH compression. We explore the impact of cost assumptions (capital and operating cost items) on the overall cost of MH compression over an assumed 10-year life. Results indicate that MH compressors have similar capital costs to currently available mechanical compressors but have a significant advantage in operating costs where waste or solar heat is available. This analysis highlights that it is the cost of energy that has the greatest impact on the cost competitiveness of the metal hydride compressor.

Hydrogen doi: 10.3390/hydrogen7010034

Authors: Eleonora Aneggi Marilda Scarbolo Daniele Zuccaccia

Hydrogen is a potential energy carrier for the decarbonization of the heating sector; however, its long-term role remains highly debated. This meta-analysis (2024–early 2025) assesses hydrogen’s potential for domestic heating regarding consumption, costs, and environmental impacts. Current scientific evidence distinguishes between hydrogen use for direct residential heating and its role in integrated energy systems. For residential decarbonization, the literature does not support hydrogen as a primary solution: electrification, especially through heat pumps, remains the most efficient and cost-effective long-term pathway. Direct hydrogen heating faces major thermodynamic and economic barriers, including low conversion efficiency, high Levelized Costs of Energy (LCOE), infrastructure limitations, and challenges in achieving broad social acceptance. Hydrogen’s more strategic value emerges at the system level. Hybrid configurations that combine heat pumps with hydrogen storage show strong potential by using heat pumps to efficiently meet thermal demand while reserving hydrogen for flexible backup and storage. In particular, hydrogen is well suited for long-term seasonal energy storage and grid balancing, enhancing system flexibility and reliability. Its main contribution therefore lies not in direct end-use heating, but in strengthening grid resilience and supporting energy autarky in net-zero scenarios. Hydrogen blending into existing gas networks is widely viewed as a transitional measure to stimulate the hydrogen economy and deliver limited short-term emission reductions, rather than a definitive net-zero solution. Overall, hydrogen’s residential role remains niche, requiring targeted research, development, and large-scale pilot projects to validate competitive applications.

Hydrogen doi: 10.3390/hydrogen7010033

Authors: Tinashe Mazarire Alexander Galloway Athanasios Toumpis

Current onboard hydrogen storage systems are volumetrically inefficient and represent a major constraint on the driving range of heavy-duty fuel cell vehicles. This work presents a conceptual model of an internally reinforced Type I rectangular-shaped pressure vessel as a solution to enhance the volumetric efficiency of hydrogen storage in heavy-duty vehicles. The pressure vessel’s geometry incorporates an internal reinforcing structure to ensure both the structural integrity of the vessel and compliance with the standards for onboard hydrogen storage. Initially, an analytical approach was employed to determine the base parameters of the wall and the internal structure of the reinforced pressure vessel. Finite element analysis was then conducted to validate the analytical solutions and assess the structural integrity of the pressure vessel under design pressure conditions. This was followed by a parametric optimisation study in which the design parameters were systematically varied to identify an optimal pressure vessel design. The 35 MPa reinforced titanium pressure vessel offers 29% more volumetric capacity than the conventional Type IV storage system. The gravimetric capacity of the titanium pressure vessel is low, 2.9 wt%; despite this, the mass of the vessel is applicable in HDVs. This design increases hydrogen storage capacity, offering a range increase of approximately 29% for the same design space.

Hydrogen doi: 10.3390/hydrogen7010032

Authors: Min Xie Xianbo Jiang Yanxuan Lu

Hydrogen, an emerging low-carbon energy carrier, is pivotal for high-penetration renewable energy and integrated energy systems, yet the coupling of hydrogen with electricity and gas for hydrogen production and enriched compression-integrated systems remains a key issue for energy transition. This study establishes the architecture and analyzes the energy flow of an urban hydrogen production and enriched compressing-integrated energy system, as well as models its hydrogen production-enriched compressing, power, and hydrogen-enriched compressed natural gas subsystems based on water electrolysis, hydrogen storage, hydrogen fuel cells (HFCs), and hydrogen-enriched compressed natural gas (HCNG) technology, and develops a low-carbon optimal scheduling model with demand response to minimize intraday economic dispatch costs. Scenario comparisons verify the model’s effectiveness, showing that the system boosts wind-solar utilization by 6.81% and cuts carbon emissions by 1.89%.

Hydrogen doi: 10.3390/hydrogen7010031

Authors: Dk Syasya Nurul Batrisyia Pg Haji Md Ali Badrin Yun Yung Liaw Miza Syahmimi Haji Rhyme Zi Hui Yong Hazwani Suhaimi Pg Emeroylariffion Abas

Hydrogen has been widely regarded as a key energy carrier. However, its storage and long-distance transportation are challenging, resulting in the emergence of ammonia as a potential carrier of hydrogen due to its high hydrogen density, ease of liquefaction, and established transport infrastructure. This study presents a techno-economic and environmental impact assessment of two methods of hydrogen production from ammonia: catalytic cracking (ACC) and electrocatalytic (AEC) decomposition, modeled under the specific local economic conditions of Brunei Darussalam. Analysis over a 20-year plant lifetime under local economic conditions indicates that the more technologically established ACC achieves a higher net present value of USD 7.298 million, compared to USD 6.867 million for AEC, primarily due to its significantly lower replacement costs. Sensitivity analysis indicates that AEC becomes economically favorable at production rates above approximately 29.5 kg/h or electricity prices exceeding USD 0.13/kWh. Environmental impact analysis indicates that AEC produces higher lifetime CO2 emissions of approximately 84.9 million kg, compared to ACC with approximately 44.0 million kg of CO2 emissions under grid-based electricity supply. This is mainly due to its higher electricity demand. Overall, the study highlights clear economic–environmental trade-offs between ACC and AEC and underscores the importance of integrated techno-economic and environmental evaluation for ammonia-based hydrogen systems in a Bruneian context.

Hydrogen doi: 10.3390/hydrogen7010030

Authors: Sharif H. Zein Yvette Kusi Agyemang Usama Ahmed Amal Al Saadi Aditya Putranto Aishah A. Jalil

Plastic waste poses a major environmental issue because it persists in nature for long durations and recycling facilities are not readily available. The conversion of waste materials into hydrogen creates two beneficial effects that help decrease pollution levels and establish hydrogen as a clean energy source for sustainable low-carbon systems. In this study, an integrated process for plastic-to-hydrogen conversion was developed using Aspen HYSYS v14. The system uses pyrolysis, steam reforming, and the water–gas shift (WGS) reaction, through pseudo-components of polyethylene, polypropylene and polystyrene to model decomposition processes. Following optimization, the hydrogen fraction in the syngas rose from 0.664 to 0.733. At this stage, the process produced roughly 651 kg of hydrogen per hour in steady operation. In addition, char and pyrolysis oil were produced as co-products that can be valorized in circular economy applications The implementation of heat integration achieved an 8% reduction in utility demand that proves that internal energy recovery stands as a vital element for sustainable design. The techno-economic analysis showed that the project would achieve a 39% internal rate of return and payback period of 5.95 years, thus proving its financial stability. The research demonstrates how modern process modeling techniques enable the creation of clean technology systems that address plastic pollution problems while producing low-carbon hydrogen.

Hydrogen doi: 10.3390/hydrogen7010029

Authors: Igor Y. Shchapin Andrey I. Nekhaev

Molecular hydrogen, the basis of hydrogen energy, is formed in many physical and chemical processes, including the absorption of gamma-ray energy by liquid cyclohexane. From the point of view of energy consumption, the stages of gamma radiolytic formation of molecular hydrogen have not been quantified. By means of a new energy method, we analyzed the amounts of released molecular hydrogen during gamma irradiation of liquid cyclohexane in the absence and presence of small additives of bicyclic mono- and dienes RH (initial concentrations of C0(RH) ≈ 5 × 10−3 M/L), depending on the first ionization potentials of the components of solutions determined in the gas phase. Using the new energy method, four primary intermediates—radical anion, electronically excited molecule, radical cation, and superexcited molecule—of liquid cyclohexane gamma radiolysis were identified. Energy, mechanistic, and spin relationships and connections between these four cyclohexane intermediates were established. The experimental value of the adiabatic electron affinity of the cyclohexane molecule is −2.01 eV. The energy of formation of the superexcited cyclohexane molecule is 18 eV (gas phase). Using the energy method, it is shown that an increase in C0(RH) concentrations from 5 × 10−3 to 0.1 M/L leads to a change in the mechanism of RH consumption. Instead of RH activation, as a result of the single electron transfer reaction, RH polymerization begins, which is initiated by cyclohexyl radicals.

Hydrogen doi: 10.3390/hydrogen7010028

Authors: Svetlana Ratner Konstantin Gomonov Sos Khachikyan Artem Shaposhnikov

This study develops an integrated analytical framework to assess Russia’s green hydrogen demand potential and cost-competitiveness pathways across the steel production and road transport sectors. Using bottom-up sectoral analysis, we estimate Russia’s theoretical hydrogen demand potential at approximately 18.2 Mt/year. Three policy scenarios model demand realization trajectories under differentiated support regimes, calibrated to European alternative fuel vehicle diffusion patterns and Russian statistical data. A learning curve framework projects green hydrogen costs as an endogenous function of cumulative production, with learning rates of 5% and 10.1% representing conservative and optimistic technology development pathways. Results indicate that under realistic policy support and 10.1% learning rates, hydrogen costs decline from USD 15/kg to USD 7.23/kg by 2050, reaching the USD 10/kg competitiveness threshold by approximately 2035. However, Russia’s costs remain 2–4 times higher than global optimal-location projections due to scale disadvantages and infrastructure constraints. Policy recommendations emphasize front-loaded support mechanisms, export market integration with EAEU partners, and electrolyzer technology localization to accelerate learning effects and achieve cost competitiveness within mid-term planning horizons.

Hydrogen doi: 10.3390/hydrogen7010027

Authors: Mohamed-Amine Babay Mustapha Adar Mohamed Essam El Messoussi Ahmed Chebak Mustapha Mabrouki

The journal retracts the article titled, “Bio-Aerodynamic Flow Field Optimization in PEM Fuel Cells: A Peregrine Falcon-Inspired Flow Field Approach” [...]

Hydrogen doi: 10.3390/hydrogen7010026

Authors: Antonio Giuffrida

The hydraulically driven piston compressor is a state-of-the-art solution for compressing hydrogen to pressure levels up to 100 MPa and even beyond, especially for use in hydrogen refueling stations. Based on the technical data of a few commercial hydraulically driven piston systems for hydrogen compression, thermodynamic calculations are developed in this paper, and a preliminary indicator, the compression-to-electric power ratio (CEPR), is assessed. In order to justify calculated CEPR values no greater than 0.42 for the analyzed compression units, attention is paid to the hydrogen compression duty, and the instantaneous power is drawn based on a simple but effective procedure. In detail, the instantaneous power profile has a peak value approximately double that of the average power, and this peak is maintained for almost half of the working period. According to this result, the electric motor must be sized correctly. Thus, it might seem over-configured if compared to the average compression power, hence the relatively low CEPR values. Finally, in order to support the current assessment of the instantaneous power, considerations about the control system for piston movement inversion are reported.

Hydrogen doi: 10.3390/hydrogen7010025

Authors: Konstantinos Letsios Nikolaos D. Charisiou Georgios S. Skodras Maria A. Goula Savvas L. Douvartzides

As hydrogen mobility gains increasing importance, the number of hydrogen refueling stations (HRSs) worldwide is expanding rapidly. Hydrogen compression is a critical component of every HRS, exerting a direct and decisive influence on operability, performance, economic viability, downtime, safety, and public acceptance. Given this central role, this work presents a comprehensive overview of the hydrogen compression landscape, critically examining both conventional mechanical systems—such as piston and diaphragm compressors—and emerging non-mechanical technologies, including electrochemical and metal hydride compressors. The analysis also addresses novel hybrid approaches that combine methods to exploit their respective strengths. Each technology is assessed against a consistent set of practical criteria, encompassing not only fundamental performance metrics such as maximum discharge pressure and flow capacity but also key considerations relevant to real-world deployment. This review provides a detailed comparison of all hydrogen compression technologies with respect to energy efficiency, maintenance needs and intervals, capital expenditures (CAPEX), operating expenditures (OPEX), and Technology Readiness Level (TRL). Additional factors—including physical size, noise levels, and effects on hydrogen purity—are also evaluated, as they strongly influence the suitability for applications in urban or remote areas. By synthesizing recent scientific literature, industry data, and applicable technical standards, this work develops a structured multi-criteria framework that translates technical insights into practical guidance and a clear technology selection roadmap. The overarching objective is to equip engineers, station developers, operators, and policymakers with the knowledge needed to make informed and optimized decisions about hydrogen compression during HRS planning and design.

Hydrogen doi: 10.3390/hydrogen7010024

Authors: Xinshu Yu Jingyi Zhang Jie Zhang Sihan Chen Yifan Lu Dongji Xuan

Proton Exchange Membrane Fuel Cells (PEMFCs) are highly valued for their zero emissions, low noise, and environmentally friendly characteristics. However, they face substantial difficulties when starting up in low-temperature conditions. Coolant-assisted heating is usually more effective than other methods because of its fast speed, high heat transfer efficiency, and simple structure. This study developed a three-dimensional multiphase non-isothermal PEMFC cold start model with coolant-assisted heating. Key parameters, including heat consumption rate, coolant flow rate, load current slope, initial membrane water content, catalyst layer porosity, and gas diffusion layer porosity, were selected as optimization variables. A Convolutional Neural Network–Attention Mechanism–Bidirectional Long Short-Term Memory Neural Network (CAB-Net) was employed as a surrogate model to predict the ice volume fraction during the cold start process. The CAB-Net model was further integrated with the Lexicographic Ordered Whale Optimization Algorithm (LO-WOA) to identify the optimal combination of parameters. The optimization aimed to minimize the maximum ice volume fraction (MIVF) in the Cathode Catalyst Layer (CCL) and reduce the energy consumption required to reach this fraction. The optimization results revealed that, compared to the baseline model (MIVF = 0.4519, energy consumption = 0.77264 J), the MIVF was reduced to 0.1471, representing a 67.45% decrease, while energy consumption was reduced to 0.70299 J, achieving a 9.01% decrease. The results underscore the efficacy of the proposed strategy in enhancing cold start performance under low-temperature conditions.

Hydrogen doi: 10.3390/hydrogen7010023

Authors: Kaveh Edalati

Hydrogen is a key energy carrier for achieving carbon neutrality, yet its widespread deployment is hindered by challenges associated with efficient hydrogen production, safe and reversible hydrogen storage, and hydrogen-induced embrittlement. Severe plastic deformation processes, particularly high-pressure torsion (HPT), have emerged as a powerful approach capable of addressing these challenges through extreme grain refinement, defect engineering, phase stabilization far from equilibrium, and synthesis of novel materials. This article reviews the impact of HPT on hydrogen-related materials, covering hydrogen production, hydrogen storage, and hydrogen embrittlement resistance. For hydrogen production, HPT enables the synthesis of nanostructured, defect-rich, and compositionally complex compounds, including high-entropy oxides and oxynitrides, which exhibit enhanced hydrolytic, electrocatalytic, photocatalytic, photoelectrocatalytic, and photoreforming performance. For hydrogen storage, HPT fundamentally modifies hydrogenation activation and kinetics, and modifies thermodynamics by hydrogen binding energy engineering, enabling reversible hydrogen storage at room temperature in systems such as Mg-based and high-entropy alloys. For hydrogen embrittlement resistance, HPT under optimized conditions suppresses hydrogen-assisted fracture by engineering ultrafine grains and defects (vacancies, dislocations, Lomer–Cottrell locks, D-Frank partial dislocations, stacking faults, twins, and grain boundaries) that control hydrogen diffusion, trapping, and strain localization. By integrating insights across these three domains, this article highlights HPT as a transformative strategy for developing next-generation hydrogen materials and identifies key opportunities for future research at the intersection of severe plastic deformation and hydrogen technologies.

Hydrogen doi: 10.3390/hydrogen7010022

Authors: Przemyslaw Komarnicki

The smart grid concept is based on the full integration of different types of energy sources and intelligent devices. Due to the short- and long-term volatility of these sources, new flexibility measures are necessary to ensure the smart grid operates stably and reliably. One option is to convert renewable energy into hydrogen, especially during periods of generation overcapacity, in order that the hydrogen that is produced can be stored effectively and used “just in time” to stabilize the power system by undergoing a reverse conversion process in gas turbines or fuel cells which then supply power to the network. On the other hand, in order to achieve a sustainable general energy system (GES), it is necessary to replace other forms of fossil energy use, such as that used for heating and other industrial processes. Research indicates that a comprehensive hydrogen supply infrastructure is required. This infrastructure would include electrolyzers, conversion stations, pipelines, storage facilities, and hydrogen gas turbines and/or fuel cell power stations. Some studies in Germany suggest that the existing gas infrastructure could be used for this purpose. Further, nuclear and coal power plants are not considered reserve power plants (as in the German case), and an additional 20–30 GW of generation capacity in H2-operated gas turbines and strong H2 transportation infrastructure will be required over the next 10 years. The novelty of the approach presented in this article lies in the development of a unified modeling framework that enables the simultaneous and coherent representation of both economic and technical aspects of hydrogen production systems which will be used for planning and pre-decision making. From the technical perspective, the model, based on the black box approach, captures the key operational characteristics of hydrogen production, including energy consumption, system efficiency, and operational constraints. In parallel, the economic layer incorporates capital expenditures (CAPEX), operational expenditures (OPEX), and cost-related performance indicators, allowing for a direct linkage between technical operation and economic outcomes. This paper describes the systematic transformation from today’s power system to one that includes a hydrogen economy, with a particular focus on practical experiences and developments, especially in the German energy system. It discusses the components of this new system in depth, focusing on current challenges and applications. Some scaled current applications demonstrate the state of the art in this area, including not only technical requirements (reliability, risks) and possibilities, but also economic aspects (cost, business models, impact factors).

Hydrogen doi: 10.3390/hydrogen7010021

Authors: Mopeli Ishmael Khama Beberto Myth Vunene Baloyi Quinn Gareth Reynolds Buhle Sinaye Xakalashe Deshenthree Chetty

Production of ferrochrome alloy is carried out using carbon as a reductant in a Submerged Arc Furnace (SAF). Carbothermic reduction of chromite ore results in high CO2 emissions, and alternative reductants such as H2, wherein H2O is the only by-product, have become attractive potential alternatives. Before utilizing H2 as a reductant, it is crucial to carry out a comprehensive study on the reaction kinetics with the view to aid the design and operation of reactors that facilitate the reduction process. The current study determined the kinetic parameters for isothermal and non-isothermal pre-reduction of chromite with H2 in a thermogravimetric furnace. Results from powder X-ray diffraction and scanning electron microscopy determined the mineralogical variations between the feed and the pre-reduced samples, as well as the variation between isothermally and non-isothermally treated samples. The mass loss data indicates that longer reduction times are required to reach complete reduction. The apparent activation energy for the isothermal and non-isothermal pre-reduction tests was found to be 105 and 124 kJ/mol, respectively. The mineralogical observations for pre-reduced samples at 1300 °C and 1500 °C showed that samples treated at lower temperatures (1300 °C) displayed consistent textures and Fe-Cr droplets along rims of partially altered chromite (PAC), which suggested higher metallization at this temperature. Higher temperatures (1500 °C), on the other hand, resulted in poor metallization, possibly because higher temperatures are often associated with a collapsed pore network, which results in poor diffusion rates, thus hindering complete reduction.

Hydrogen doi: 10.3390/hydrogen7010020

Authors: Theodor Mihnea Sîrbu Cristi Emanuel Iolu Tudor Prisecaru

This review examines the combustion characteristics of hydrogen-enriched natural gas with a specific focus on residential appliances, where safety, efficiency, and emission performance are critical. Drawing on experimental studies, numerical simulations, and regulatory considerations, the paper synthesizes current knowledge on how hydrogen addition influences flame stability, flashback phenomenon, thermal efficiency, pollutant formation, and flame geometry. Results across cooktop burners, boilers, and other domestic systems show that moderate hydrogen blending not only can reduce CO and CO2 emissions and enhance combustion efficiency but also can increase burning velocity, diffusivity, and flame temperature, thereby elevating flashback and NOx risks. The review highlights the blending limits, design adaptations, and operational strategies required to ensure safe and effective integration of hydrogen into residential gas infrastructures, supporting its role as a transitional low-carbon fuel.

Hydrogen doi: 10.3390/hydrogen7010019

Authors: Maxime Mussard Marc De Huu Rémy Maury Loucie Cirkeline Nordhjort Mjølna Tomáš Valenta Mahdi Sadri Eric Starke Pieter Pinson Marcel Workamp Adriaan M. H. van der Veen

We present the first European intercomparison of primary flow measurement standards with hydrogen-enriched natural gas (up to 20% hydrogen in molar fraction) and natural gas with pressure up to 60 bar and volume flow rates in the range (5 to 160) m3/h. We describe the principles of operation of the primary standards and present the transfer standards, a rotary meter and an ultrasonic meter, used for the intercomparison. In many instances, the overlap between the different laboratories is satisfactory, but the collected results are limited and do not allow us to make advanced conclusions. In addition, we investigate the effect of nitrogen impurities (2% in molar fraction) on the performance of low-pressure gas meters for pure hydrogen using newly developed measurement standards. We present the methods and results of this investigation. We show that nitrogen impurities affect the volume flow measurements of an ultrasonic meter but seem to have little effect on a thermal mass flow meter. This paper explores future opportunities and challenges in international intercomparisons involving hydrogen blends and highlights key issues and solutions with hydrogen gas metering in the presence of impurities.

Hydrogen doi: 10.3390/hydrogen7010018

Authors: Glenn McRae Christopher Coleman

Experimental results are compiled to show apparent hysteresis seen in hydride thermal precipitation–dissolution cycling in zirconium alloys using X-ray diffraction, dynamic elastic modulus techniques, and differential scanning calorimetry (DSC). Gibbs’ phase rule is used to justify a description of a stable hydride in the H-Zr system in terms of a control volume with a hydride at its core, surrounded by a stress gradient that produces a stabilizing gradient of hydrogen in the solution. The conditions for a stable hydride are derived when the flux of hydrogen in solid solution is zero. DSC heat flow curves are analyzed with a thermodynamic model that predicts concentrations of hydrogen in a solution during temperature cycling and a description of experimental results that show how concentrations evolve at a constant temperature to the same final state when cycling is paused, from which hysteresis is deemed an illusion. The control volume is supported by previous energy calculations, performed with density functional theory. Implications of replacing the order parameter for phase field methods with the gradient of the yield stress are discussed. A practical method for forming a stable hydride is presented.

Hydrogen doi: 10.3390/hydrogen7010017

Authors: Robinson Aguirre Ocampo Julian Arias-Velandia Julian A. Lenis Alejandro A. Zuleta Gil Sindy Bello Esteban Correa Carlos E. Arrieta Francisco J. Bolívar Félix Echeverria Echeverria

Magnesium has significant potential for hydrogen storage in the solid state because its capacity is about 7.6 wt%. However, the high stability of magnesium hydride requires operating temperatures superior to 380 °C for hydrogen release. It is well known that Ni could catalyze the hydrogen absorption and desorption in magnesium. In this study, carbon-coated nickel nanoparticles were employed as catalysts to enhance the hydrogen absorption and desorption kinetics of pre-hydrogenated magnesium particles. The carbon-coated nickel nanoparticles were uniformly dispersed across the surface of the pre-hydrogenated magnesium particles. In dehydrogenation at 375 °C and 350 °C, the best sample desorbs 4.90 and 4.1 wt%, respectively, in 10 min. After 45 cycles at 375 °C, the hydrogen desorption capacity is 4.91 wt%, indicating a retention capacity of 100%. Our results demonstrate that carbon-coated nickel nanoparticles can be effectively incorporated into pre-hydrogenated magnesium without the need for ball milling, significantly enhancing hydrogen absorption and desorption performance.

Hydrogen doi: 10.3390/hydrogen7010016

Authors: Miza Syahmimi Haji Rhyme Dk Nur Hayati Amali Pg Haji Omar Ali Hazwani Suhaimi Pg Emeroylariffion Abas

With rising demand for clean energy and uncertainty surrounding large-scale renewable deployment, ammonia has emerged as a viable carrier for hydrogen storage and transportation. This study conducts a global patent-based analysis of ammonia-to-hydrogen production technologies to determine technological maturity, dominant design pathways, and emerging innovation trends. A statistically robust retrieval, screening, and classification process, based on the PRISMA guidelines, was employed to screen, sort, and analyze 708 relevant patent families systematically. Patent families were categorized according to synthesis processes, catalyst types, and technological fields. The findings indicate that electrochemical, plasma-based, photocatalytic, and hybrid systems are being increasingly investigated as alternatives to low-temperature processes. At the same time, thermal catalytic cracking remains the most established and widely used method. Significant advances in reactor engineering, system integration, and catalyst design have been observed, especially in Asia. While national hydrogen initiatives, such as those in Brunei, highlight the policy importance of ammonia-based hydrogen systems, the findings primarily provide a global overview of technological maturity and innovation trajectories, thereby facilitating long-term transitions to cleaner hydrogen pathways.

Hydrogen doi: 10.3390/hydrogen7010015

Authors: Alvin Garcia Palanca Cherry Lyn Velarde Chao Kristian July R. Yap Rizalinda L. de Leon

This study introduces an integrated Life Cycle Assessment–Multi-Criteria Decision Analysis–Nash Equilibrium (LCA–MCDA–NE) framework to assess the feasibility of hydrogen energy storage (HES) in Philippine island grids. It starts with a cradle-to-gate LCA of hydrogen production across various electricity mix scenarios, from diesel-dominated Small Power Utilities Group (SPUG) systems to high-renewable configurations, quantifying greenhouse gas emissions. These impacts are normalized and integrated into an MCDA framework that considers four stakeholder perspectives: Regulatory (PRF), Developer (DF), Scientific (SF), and Local Social (LSF). Attribute utilities for Maintainability, Energy Efficiency, Geographic–Climatic Suitability, and Regulatory Compliance inform a 2 × 2 strategic game where net utility gain (Δ) and switching costs (C1, C2) influence adoption behavior. The findings indicate that the baseline Nash Equilibrium favors non-adoption due to limited utility gains and high switching barriers. However, enhancements in Maintainability and reduced costs can shift this equilibrium toward adoption. The LCA results show that meaningful decarbonization occurs only when low-carbon generation exceeds 60% of the electricity mix. This integrated framework highlights that successful HES deployment in remote grids relies on stakeholder coordination, reduced risks, and access to low-carbon electricity, offering a replicable model for emerging economies.

Hydrogen doi: 10.3390/hydrogen7010014

Authors: Néstor Velaz-Acera Cristina Sáez Blázquez Víctor Casado-Lorenzo Susana Lagüela

Renewable hydrogen has become a versatile technology that can play a key role in the deployment of energy communities, although technological, economic, environmental, legal, and social challenges remain to be addressed. This study conducts a systematic review based on the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) methodology that analyzes the current state of technologies, the different applications, challenges and limitations, and future lines of research related to the enabling role of hydrogen in energy communities. Results from the bibliometric analysis show sustained growth in the number of publications over the last five years (2020–2025), with a predominance of applications in which hydrogen is combined with other energy carriers (58%). The versatility of hydrogen has prompted the evaluation of different applications, with particular emphasis on energy storage to capitalize on energy surpluses (51%), mobility (19%), and heating (20%). The main existing barriers come from the absence of stable long-term regulation, interoperability between components and technologies, and a lack of real data. Overcoming these challenges should be based on new technologies such as artificial intelligence and the construction and operation of pilot projects. In addition, a Strengths, Weaknesses, Opportunities and Threats (SWOT) analysis has been conducted building upon the SHARED-H2 SUDOE project, yielding particularly insightful results through the active involvement of stakeholders in the preparatory process. Based on all the points given above, the research concludes that it is necessary to improve long-term policies and increase training at all levels aimed at active end-user participation and a profound restructuring of the energy system.

Hydrogen doi: 10.3390/hydrogen7010013

Authors: Mmesoma Mario Alaneme Zoheir Farhat

This study evaluates the hydrogen embrittlement (HE) resistance of nickel-based electroplated coatings applied on cold-finished mild steel, with emphasis on their performance as diffusion barriers to impede hydrogen ingress. Nickel coatings were deposited using Watts plating bath under controlled electroplating parameters. Electrochemical hydrogen charging was performed in an alkaline medium at progressively increasing charging current densities to simulate varying levels of hydrogen exposure. Tensile testing was conducted immediately after charging to assess the mechanical response of both uncoated and nickel-coated specimens, focusing on key properties such as elongation, yield strength, ultimate tensile strength, and toughness. The results revealed a gradual degradation in ductility and toughness for the uncoated steel samples with increasing hydrogen content. In contrast, the nickel-coated specimens maintained mechanical stability up to a critical hydrogen threshold, beyond which a pronounced reduction in tensile response was observed. Fractographic analysis supported these trends, revealing a transition from ductile to brittle fracture characteristics with increasing concentrations of hydrogen. These findings highlight the protective capabilities and limitations of nickel-based coatings in mitigating hydrogen-induced degradation, offering insights into their application in industries where hydrogen embrittlement of structural materials is a major concern.

Hydrogen doi: 10.3390/hydrogen7010012

Authors: Ahmad Abuyahya Eyad A. Feilat Anas Abuzayed

This study presents a comprehensive techno-economic assessment to optimize a hybrid renewable energy system for green hydrogen production in Jordan. Using the Hybrid Optimization Model for Electric Renewables (HOMERs) and System Advisor Model (SAM) software, this study evaluates multiple cost projections for 2030 technology costs. Key parameters such as capital cost, efficiency, and lifetime are varied extensively. Highlighted results show a wide range in the Levelized Cost of Hydrogen (LCOH), reaching 1.59 to 3.49 USD/kg, and the Levelized Cost of Energy (LCOE) from 0.0072 to 0.0301 USD/kWh. Furthermore, Net Present Value (NPV) spans from USD 424 to 927 million, depending on the scenario and sensitivity case. Technically, the system’s optimized capacities vary significantly. PV ranges from 203 to 457 MW, wind capacities range from 0 to 220 MW, and electrolyzers range from 192 to 346 MW, demonstrating the flexibility required to meet different cost and performance assumptions. The study’s broad relevance extends to developing countries with grid constraints, where off-grid green hydrogen production is feasible. Its framework can be adapted globally, offering valuable insights.

Hydrogen doi: 10.3390/hydrogen7010011

Authors: Moe Thiri Zun Benjamin Craig McLellan

Many nations have been investing in hydrogen energy in the most recent wave of development and numerous projects have been proposed, yet a substantial share of these projects remain at the conceptual or feasibility stage and have not progressed to final investment decision or operation. There is a need to identify initial potential sites for green hydrogen production from renewable energy on an objective basis with minimal upfront cost to the investor. This study develops a decision support system (DSS) for identifying optimal locations for green hydrogen production using solar and wind resources that integrate economic, environmental, technical, social, and risk and safety factors through advanced Multi-Criteria Decision Making (MCDM) techniques. The study evaluates alternative weighting scenarios using (a) occurrence-based, (b) PageRank-based, and (c) equal weighting approaches to minimize human bias and enhance decision transparency. In the occurrence-based approach (a), renewable resource potential receives the highest weighting (≈34% total weighting). By comparison, approach (b) redistributes importance toward infrastructure and social indicators, yielding a more balanced representation of technical and economic priorities and highlighting the practical value of capturing interdependencies among indicators for resource-efficient site selection. The research also contrasts the empirical and operational efficiencies of various weighting methods and processing stages, highlighting strengths and weaknesses in supporting sustainable and economically viable site selection. Ultimately, this research contributes significantly to both academic and practical implementations in the green hydrogen sector, providing a strategic, data-driven approach to support sustainable energy transitions.

Hydrogen doi: 10.3390/hydrogen7010010

Authors: Ayann Tiam Sarath Poda Marshall Watson

The increasing global demand for clean hydrogen necessitates production methods that minimize greenhouse gas emissions while being scalable and economically viable. Hydrogen has a very high gravimetric energy density of about 142 MJ/kg, which makes it a very promising energy carrier for many uses, such as transportation, industrial processes, and fuel cells. Methane pyrolysis has emerged as an attractive low-carbon alternative, decomposing methane (CH4) into hydrogen and solid carbon while circumventing direct CO2 emissions. Still, the process is very endothermic and has always depended on fossil-fuel heat sources, which limits its ability to run without releasing any carbon. This review examines the integration of geothermal energy and methane pyrolysis as a sustainable heat source, with a focus on Enhanced Geothermal Systems (EGS) and Closed-Loop Geothermal (CLG) technologies. Geothermal heat is a stable, carbon-free source of heat that can be used to preheat methane and start reactions. This makes energy use more efficient and lowers operating costs. Also, using flared natural gas from remote oil and gas fields can turn methane that would otherwise be thrown away into useful hydrogen and solid carbon. This review brings together the most recent progress in pyrolysis reactors, catalysts, carbon management, geothermal–thermochemical coupling, and techno-economic feasibility. The conversation centers on major problems and future research paths, with a focus on the potential of geothermal-assisted methane pyrolysis as a viable way to make hydrogen without adding to the carbon footprint.

Hydrogen doi: 10.3390/hydrogen7010009

Authors: Marisol Ibarra-Rodríguez Celene Y. Fragoso-Fernández Sharon Rosete-Luna Mario Sánchez

Hydrogen storage technologies are improving over time, such as in the case of hydrogen adsorption in systems, which has been investigated in various experimental ways, as well as with theoretical methods. The design of systems that meet the needs of their experimental application is one of the challenges of these days. There are different strategies to generate adsorption of more hydrogen molecules, and several research groups have chosen to use alkali metal atoms to cause better interactions between surfaces and hydrogen molecules. Carbon, silicon, boron, phosphorus, and other systems have been reported, with carbon nanostructures being the most widely used. This review describes theoretical studies based on the addition of lithium atoms to various materials to increase the adsorption properties of hydrogen molecules.

Hydrogen doi: 10.3390/hydrogen7010008

Authors: Roberta Tatti Nejc Klopčič Fabian Radner Christian Zinner Alexander Trattner

Reducing CO2 emissions in transport requires sustainable alternatives such as fuel cell electric vehicles. A critical challenge is the efficient and safe storage and fast refueling of hydrogen at 70 MPa. This study proposes a practical design-support tool to optimize hydrogen storage systems for heavy-duty vehicles with capacities up to 100 kg. A customizable, dynamic Matlab-Simulink model was developed, including all components from dispenser to onboard tanks, enabling evaluation of multiple design options. The aim is to provide clear guidelines to ensure fast, safe, and complete refueling compliant with SAE J2601-5 limits. Simulations showed Type III tanks deliver the best performance. The fastest refueling (~10 min) was achieved with shorter pipes, larger diameters and low temperatures (20 °C ambient, −40 °C dispenser), while Average Pressure Ramp Rate was maximized up to 9 MPa/min (220 g/s of hydrogen from the dispenser) without exceeding SAE limits for pressure and temperature.

Hydrogen doi: 10.3390/hydrogen7010007

Authors: Wagd Ajeeb

Decarbonizing industry, improving urban sustainability, and expanding clean energy use are key global priorities. This study presents a techno-economic analysis (TEA) and life-cycle assessment (LCA) of green hydrogen (GH2) production via water electrolysis for low-carbon applications in the Central Asian region, with Uzbekistan considered as a representative case study. Solar PV and wind power are used as renewable electricity sources for a 44 MW electrolyzer. The assessment also incorporates recent advances in alkaline water electrolyzers (AWE) enhanced with metal–organic framework (MOF) materials, reflecting improvements in efficiency and hydrogen output. The LCA, performed using SimaPro, evaluates the global warming potential (GWP) across the full hydrogen production chain. Results show that the MOF-enhanced AWE system achieves a lower levelized cost of hydrogen (LCOH) at 5.18 $/kg H2, compared with 5.90 $/kg H2 for conventional AWE, with electricity procurement remaining the dominant cost driver. Environmentally, green hydrogen pathways reduce GWP by 80–83% relative to steam methane reforming (SMR), with AWE–MOF delivering the lowest footprint at 1.97 kg CO2/kg H2. In transport applications, fuel cell vehicles powered by hydrogen derived from AWE–MOF emit 89% less CO2 per 100 km than diesel vehicles and 83% less than using SMR-based hydrogen, demonstrating the substantial climate benefits of advanced electrolysis. Overall, the findings confirm that MOF-integrated AWE offers a strong balance of economic viability and environmental performance. The study highlights green hydrogen’s strategic role in the Central Asian region, represented by Uzbekistan’s energy transition, and provides evidence-based insights for guiding low-carbon hydrogen deployment.

Hydrogen doi: 10.3390/hydrogen7010006

Authors: Yong Li Zhiwei Wang Qifu Lin Dianwu Wu Jiawei Gong Zhicong Lv Yuchen Zhang Longwei Chen

Ammonia serves as a critical medium for hydrogen storage and energy transportation, making the development of efficient ammonia cracking technologies essential for advancing hydrogen energy applications. Plasma-assisted ammonia cracking has emerged as a promising approach for clean energy conversion, leveraging non-thermal plasma to effectively decompose ammonia into hydrogen and nitrogen. Compared to conventional thermal catalytic cracking, this method offers several advantages, including rapid startup and response, operational flexibility, and the ability to operate under low-temperature and atmospheric pressure conditions. This study presents a novel high-pressure plasma reactor designed to overcome the high-energy barriers associated with conventional methods. Through systematic optimization of discharge parameters, reactor configuration, and catalyst integration, significant improvements in both ammonia conversion efficiency and energy utilization have been achieved. Experimental results demonstrate that increased discharge power and reduced ammonia flow rate enhance cracking performance. In the absence of a catalyst, conversion efficiency initially increases with pressure but subsequently decreases at higher pressures. However, the incorporation of a catalyst markedly improves overall performance across all tested conditions. These advancements support the practical implementation of ammonia-based systems for distributed hydrogen supply and clean propulsion technologies.

Hydrogen doi: 10.3390/hydrogen7010005

Authors: Saad Fahim Taoufiq Kaoutari Guillaume Foin Hasna Louahlia

This paper investigates three distinct hydrogen-related subsystems: production, storage, and the use. An analysis of the micro-combined heat and power production (mCHP) behavior using natural gas is conducted to understand how the system operates under different conditions and to evaluate its yearly performance. To reduce CO2 emissions, hydrogen fuel consumption is proposed, and an emission analysis under different fuel-supply configurations is performed. The results show that hydrogen produced by artificial photosynthesis has the lowest CO2 impact. Therefore, the paper examines this process and its main characteristics. An engineering model is proposed to rapidly estimate the mean volumetric hydrogen production rate. To ensure safe coupling between hydrogen production and mCHP demand, the study then focuses on solid-state hydrogen storage. Subsequently, in this framework, the state of charge (SOC) is defined as the central control variable linking storage thermodynamics to hydrogen delivery. Accurate SOC estimation ensures that the storage unit can supply the required hydrogen flow without causing starvation, pressure drops, or thermal drift during CHP operation. The proposed SOC estimation method is based on an analytical approach and experimentally validated while relying solely on external measurements. The overall objective is to enable a coherent, low-carbon, and safely controllable hydrogen-based mCHP system.

Hydrogen doi: 10.3390/hydrogen7010004

Authors: Jesús Rey Cirilo Delgado Francisca Segura José Manuel Andújar

The deployment of electrolysis-based hydrogen technology requires identifying the advantages and disadvantages of scaling hydrogen production plants and determining the limits of the scaling-up process. Until now, experience has been demonstrated with electrolysers of tens and hundreds of kilowatts, but electrolysers in the tens of megawatts range are still closer to being prototypes than commercial products. Additionally, challenges such as maintenance, reliability, long-term operation, and investment recovery time arise in parallel as the scale increases. This raises the question of what is more suitable: installing a single high-power electrolyser or a modular plant composed of multiple smaller electrolysers? This paper addresses that question from both a technical and an economic perspective. Accordingly, it presents a study identifying the degree of modularisation that optimises the technical and economic performance of a large-scale hydrogen production plant. The results show that configurations with a higher degree of modularisation (based on multiple smaller electrolysers) exhibit a better technical performance and lower degradation. However, configurations with a lower degree of modularisation are more competitive in terms of costs. When combining technical and economic criteria, the results show that solutions based on a medium–low degree of modularisation are the most suitable. The advantages are lower replacement costs and uninterrupted hydrogen production. This study also recommends embracing modularisation to prevent a dependence on a single high-power electrolyser.

Hydrogen doi: 10.3390/hydrogen7010003

Authors: Koki Tsunematsu Hiroki Miyaoka Takayuki Ichikawa

Recently, the kinetic improvement of the nitrogenation reaction of lithium hydride (LiH) to form lithium imide (Li2NH) by adding a scaffold was reported. The scaffold prevents agglomeration of Li2NH and maintains the activity of LiH, achieving a reduction in reaction temperature and an increase in reaction rate. In this work, a Li–Si alloy, Li22Si5, was used as a starting material to form nano-sized LiH dispersed in a Li alloy matrix. Lithium nitride (Li3N) is generated by the reaction between Li22Si5 and N2 to form Li7Si3, and then Li3N is converted to LiH with ammonia (NH3) generation during heat treatment under H2 flow conditions. Since Li3N is formed at the nano-scale on the surface of alloy particles, LiH generated from the above nano-Li3N is also nano-scale. The differential scanning calorimetry results indicate that direct nitrogenation of LiH in the alloy matrix occurred from around 280 °C, which is much lower than that of the LiH powder itself. Such a highly active state might be achieved due to the nano-crystalline LiH confined by the Li alloy as a self-transformed scaffold. From the above experimental results, the nano-confined LiH in the alloy matrix was recognized as a potential NH3 synthesis technique based on the LiH-Li2NH type chemical looping process.

Hydrogen doi: 10.3390/hydrogen7010002

Authors: Daniil A. Sundukov Olga V. Levitskaya Tatiana V. Pleteneva Anton V. Syroeshkin

Chemical incompatibility between active pharmaceutical ingredients (APIs) and mineral supplements may affect their bioavailability and effectiveness. Water, as the main component of physiological fluids, plays a crucial role in these interactions. Natural waters vary in the deuterium. Estimation of the kinetic isotope effect (KIE) provides valuable information on reaction mechanisms in solvents with different D/H ratios and with the replacement of protium with deuterium in API molecules. Studies of the kinetics of interactions between zinc ions and amoxicillin in water with a natural isotopic composition (D/H = 145 ppm) and in heavy water (99.9% D2O) offer a model for predicting similar interactions in vivo. The presence of chiral centers in the amoxicillin molecule allowed the use of polarimetry to study the influence of the solvent isotopic composition, temperature, and pH on the rate of interaction. In heavy water, a twofold decrease in the rate of amoxicillin binding to hydrated zinc ions was observed compared to natural water at 20 °C. Arrhenius kinetics confirmed the observed KIE: Ea = 112.5 ± 1.3 kJ/mol for D2O and 96.0 ± 2.1 kJ/mol for H2O. For the first time, kinetic polarimetric studies demonstrated differences in the mechanisms of binding of d- and s-element cations to amoxicillin.

Hydrogen doi: 10.3390/hydrogen7010001

Authors: Salaki Reynaldo Joshua Kenneth Yosua Palilingan Salvius Paulus Lengkong Sanguk Park

The integration of solar photovoltaic (PV) systems into smart grids necessitates robust, real-time fault detection mechanisms, particularly in resource-constrained environments like the Solar–Hydrogen AIoT microgrid framework at a university. This study conducts a comparative analysis of four prominent Convolutional Neural Network (CNN) architectures VGG16, ResNet-50, DenseNet121, and EfficientNetB0 to determine the optimal model for low-latency, edge-based fault diagnosis. The models were trained and validated on a dataset of solar panel images featuring multiple fault types. Quantitatively, DenseNet121 achieved the highest classification accuracy at 86.00%, demonstrating superior generalization and feature extraction capabilities. However, when considering the stringent requirements of an AIoT system, computational efficiency became the decisive factor. EfficientNetB0 emerged as the most suitable architecture, delivering an acceptable accuracy of 80.00% while featuring the smallest model size (5.3 M parameters) and a fast inference time (approx. 26 ms/step). This efficiency-to-accuracy balance makes EfficientNetB0 ideal for deployment on edge computing nodes where memory and real-time processing are critical limitations. DenseNet121 achieved 86% accuracy, while EfficientNetB0 achieved 80% accuracy with lowest model size and fastest inference time. This research provides a validated methodology for implementing efficient deep learning solutions in sustainable, intelligent energy management systems. The novelty of this work lies in its deployment-focused comparison of CNN architectures tailored for real-time inference on resource-constrained Solar–Hydrogen AIoT systems.

Hydrogen doi: 10.3390/hydrogen6040124

Authors: Hisashi Kosaka Khanh Van Nguyen Kosuke Matsui Hideyuki Matsushima Takumi Miyauchi Gozo Kiguchi Hidekazu Yamamoto Tung Thanh Lai Hoang Hai Duong Keita Mori Hideki Ishikawa Masaki Kaibori

Hydrogen has antioxidant and anti-inflammatory properties that may attenuate perioperative stress responses. However, its clinical impact on postoperative recovery remains unclear. This randomized, double-blind, placebo-controlled trial evaluated whether perioperative hydrogen inhalation improves early recovery after hepatectomy. Sixty-eight patients undergoing elective hepatectomy were randomized (1:1) to receive 5% hydrogen gas or placebo air via nasal cannula from postoperative day (POD) 1 to POD7. The primary endpoint was the total Quality of Recovery-40 (QoR-40) score on POD3, analyzed at α = 0.2 with 80% confidence intervals in accordance with the pre-specified statistical analysis plan. Secondary and exploratory outcomes, analyzed at α = 0.05, included postoperative liver function, oxidative stress markers, and QoR-40 subdomain scores. Analyses were performed in the modified intention-to-treat population using the Mann–Whitney U test. Sixty-four patients (hydrogen, n = 31; placebo, n = 33) were analyzed. At POD3, the median QoR-40 score was 192.0 (184.0–198.0) vs. 163.0 (140.0–190.0) (p < 0.001), indicating significantly better early recovery in the hydrogen group. As supportive findings, prothrombin activity was higher with hydrogen (85.0% vs. 76.2%, p = 0.005), and QoR-40 subdomain analysis showed significantly higher emotions and physical independence scores, whereas comfort, pain, and patient support domains showed no difference. No other between-group differences were observed in biochemical parameters or urinary 8-OHdG levels. Perioperative hydrogen inhalation significantly improved early postoperative recovery after hepatectomy, primarily through psychophysical domains of well-being. These findings suggest that hydrogen may selectively enhance emotional stability and functional independence during the early recovery phase.

Hydrogen doi: 10.3390/hydrogen6040123

Authors: Alan Kenzhiyev Viktor N. Kudiiarov Alena A. Spiridonova Daria V. Terenteva Dmitrii B. Vrublevskii Leonid A. Svyatkin Dmitriy S. Nikitin Egor B. Kashkarov

The composite material MgH2-EEWNi-Cr (20 wt. %) with a hydrogen content of 5.2 ± 0.1 wt.% is characterized by improved hydrogen interaction properties compared to the original MgH2. The dissociation of the material occurs in three temperature ranges (86–117, 152–162, and 281–351 °C), associated with a complex of effects consisting of changes in the specific surface area of the material, alterations in the crystal lattice during ball milling, and changes in the electronic structure in the presence of a Ni–Cr catalyst, based on first-principles calculations. The decrease in desorption activation energy (Ed = 65–96 ± 1 kJ/mol, ΔEd = 59–90 kJ/mol) is due to the catalytic effect of N–Cr, leading to a faster decomposition of the hydride phase. Based on the results of ab initio calculations, Ni–Cr on the MgH2 surface leads to a significant decrease in hydrogen binding energy (ΔEb = 60%) compared to pure magnesium hydride due to the formation of Ni–H and Cr–H covalent bonds, which reduces the degree of H–Mg ionic bonding. The results obtained allow us to expand our understanding of the mechanisms of hydrogen interaction with storage materials and the possibility of using these as mobile hydrogen storage and transportation materials.

Hydrogen doi: 10.3390/hydrogen6040122

Authors: Lucas M. Claussner Giordano Emrys Scarponi Federico Ustolin

The use of liquid hydrogen (LH2) as an energy carrier is gaining traction across sectors such as aerospace, maritime, and large-scale energy storage due to its high gravimetric energy density and low environmental impact. However, the cryogenic nature of LH2, with storage temperatures near 20 K, poses significant thermodynamic and safety challenges. This review consolidates the current state of modelling approaches used to simulate LH2 behaviour during storage and transfer operations, with a focus on improving operational efficiency and safety. The review categorizes the literature into two primary domains: (1) thermodynamic behaviour within storage tanks and (2) multi-phase flow dynamics in storage and transfer systems. Within these domains, it covers a variety of phenomena. Particular attention is given to the role of heat ingress in driving self-pressurization and boil-off gas (BoG) formation, which significantly influence storage performance and safety mechanisms. Eighty-one studies published over six decades were analyzed, encompassing a diverse range of modelling approaches. The reviewed literature revealed significant methodological variety, including general analytical models, lumped-parameter models (0D/1D), empirical and semi-empirical models, computational fluid dynamics (CFD) models (2D/3D), machine learning (ML) and artificial neural network (ANN) models, and numerical multidisciplinary simulation models. The review evaluates the validation status of each model and identifies persistent research gaps. By mapping current modelling efforts and their limitations, this review highlights opportunities for enhancing the accuracy and applicability of LH2 simulations. Improved modelling tools are essential to support the design of inherently safe, reliable, and efficient hydrogen infrastructure in a decarbonized energy landscape.

Hydrogen doi: 10.3390/hydrogen6040121

Authors: Lovisa Panduleni Johannes Nguyen Van Thinh Md Sahed Hasan Nguyen Thi Hai Anh Tran Dang Xuan

Rice husk (RH) is a widely available lignocellulosic residue for biohydrogen production but requires effective pretreatment to overcome lignin-related recalcitrance. This study investigates the kinetics of lignin removal from RH using 3% sodium hydroxide (NaOH) and water pretreatments at high temperatures between 100 and 129 °C (25 °C control) with short reaction times (15–60 min) in an autoclave system. Biomass composition, solid yield, delignification efficiency, and enzymatic hydrolysis for glucose production were evaluated. NaOH pretreatment achieved up to 72.72% lignin removal at 129 °C after 60 min, significantly outperforming water pretreatment, which reached a maximum delignification of 20.24% under the same conditions. Kinetic analysis revealed first-order reaction behavior, with the kinetic rate constants varying between 5.14 × 10−5 and 4.31 × 10−3 with water pretreatment and from 3.73 × 10−4 to 2.46 × 10−2 with NaOH and activation energies of 42.61 kJ mol−1 K−1 and 39.31 kJ mol−1 K−1 for water and NaOH pretreatment, respectively. Enhanced lignin removal improved cellulose accessibility, resulting in glucose yields from enzymatic hydrolysis of up to 52.13 mg/g for NaOH-treated samples, double those obtained with water pretreatment (26.97 mg/g). While NaOH pretreatment achieved higher lignin removal efficiency and glucose yield, it exhibited significantly higher environmental impacts across multiple categories, including global warming potential and terrestrial ecotoxicity, based on the life cycle assessment (LCA). Even water-based pretreatment showed considerable burdens; thus, both pretreatment methods impose high life cycle impacts when applied to RH, which makes it an unsustainable feedstock for glucose production under the evaluated conditions. Alternative feedstocks or improved process integration strategies are required for environmentally viable biohydrogen production.

Hydrogen doi: 10.3390/hydrogen6040120

Authors: Junwei Yan Zhangzhang Xie

Dark fermentative hydrogen production is constrained by challenges including low hydrogen yield and operational instability. Magnetic nanoparticles (MNPs) have emerged as promising additives for enhancing biohydrogen production due to their unique physicochemical characteristics, such as high specific surface area, excellent electrical conductivity, and inherent magnetic recyclability. This review systematically compares the enhancement mechanisms of MNPs in two distinct microbial systems: pure cultures and mixed cultures. In pure cultures, MNPs function primarily at the cellular and molecular levels through the following: (1) serving as sustained-release sources of essential metallic cofactors like Fe and Ni to promote hydrogenase synthesis and activation; (2) acting as efficient electron carriers that facilitate intracellular and extracellular electron transfer; and (3) redirecting central carbon metabolism toward high-hydrogen-yield acetate-type fermentation. In mixed cultures, which are more representative of practical applications, MNPs operate at the ecological level through the following: (1) modifying microenvironmental niches to exert selective pressure that enriches hydrogen-producing bacteria, such as Clostridium; (2) forming conductive networks that promote direct interspecies electron transfer and strengthen syntrophic metabolism; and (3) enhancing system robustness via toxin adsorption and pH buffering. Despite promising phenomenological improvements, critical knowledge gaps remain, including unclear structure–activity relationships of MNPs, insufficient quantification of electron transfer pathways, unknown genetic regulatory mechanisms, and overlooked magnetobiological effects. Future research should integrate electrochemical monitoring, multi-omics analyses, and advanced characterization techniques to deepen the mechanistic understanding of nanomaterial–microbe interactions. This review aims to provide theoretical insights and practical strategies for developing efficient and sustainable MNP–microorganism hybrid systems for scalable biohydrogen production.

Hydrogen doi: 10.3390/hydrogen6040119

Authors: Vyacheslav S. Protsenko Denys A. Shaiderov Oleksandr D. Sukhatskyi

This work reports the electrochemical behavior of a nickel hydroxide electrode, electrodeposited in a deep eutectic solvent (DES), in alkaline solutions of varying composition, aiming to elucidate the influence of the cation (Na+ vs. K+), urea, and carbonate ions on the mechanism and kinetics of anodic processes. Cyclic voltammetry and electrochemical impedance spectroscopy were employed to analyze the electrochemical responses of electrode processes in alkaline water electrolysis systems. For the urea oxidation reaction (UOR), the frequency-dependent characteristics were thoroughly characterized, and the impedance response was simulated according to the Armstrong–Henderson equivalent circuit. It was found that the addition of urea significantly transforms the impedance structure, sharply reducing the polarization resistance and increasing the pseudo-capacitive component of the constant phase element at low frequencies, indicating activation of the slow steps of urea oxidation via a direct mechanism and the formation of an extended adsorptive surface. It was demonstrated that, unlike conventional alkaline electrolysis where KOH-based systems are generally more effective, urea-assisted systems exhibit superior performance in NaOH-based electrolytes, which provides more favorable kinetics for the electrocatalytic urea oxidation process. Furthermore, the accumulation of carbonate ions was shown to negatively affect UOR kinetics by increasing polarization resistance and partially blocking surface sites, highlighting the necessity of controlling electrolyte composition in practical systems. These findings open new opportunities for the rational design of efficient urea-assisted electrolyzers for green hydrogen generation.

Hydrogen doi: 10.3390/hydrogen6040118

Authors: Edgar Eduardo Cedillo Cornejo Rogelio González Oropeza Stephen Samuel William Vicente Rodolfo Sosa Echeverría Elías Granados Hernández Gilberto Fuentes García Graciela Velasco-Herrera Sánchez Pablo Álvarez

Using hydrogen in compression-ignition internal combustion engines can reduce pollutant emissions and improve performance by enabling faster and more complete combustion. However, it is essential to determine the optimal injection timing and duration for both hydrogen and conventional fuels. These factors are critical in engine modeling analysis. This study aimed to analyze pollutant emissions, combustion, and engine performance with oxyhydrogen fumigation applied to an instrumented Ricardo E6 engine running on diesel fuel. This analysis, necessary for developing a new predictive combustion model, was calibrated with experimental data in the Gamma Technologies Suite (GTS) simulator. The results show four main effects when increasing the oxyhydrogen flow rate from 0 to 2.8 L per minute (LPM), at an indicated mean effective pressure (IMEP) of 5.3 bar and a speed of 1500 RPM: (I) NOx levels increased by up to 6%, (II) CO2 levels decreased by 8%, (III) combustion durations remained relatively stable, and (IV) brake specific fuel consumption decreased by 8%. Overall, adding hydrogen to the intake flow of the compression-ignition engine reduced CO2 emissions and enhanced indicated thermal efficiency.

Hydrogen doi: 10.3390/hydrogen6040117

Authors: Jocelyn Sabatier Ryma Chouder Jean-Pierre Bedecarrats Jean-Louis Bobet Fabrice Mauvy Matthieu Faessel

This work explores water hydrolysis using magnesium as a decentralized dihydrogen source for off-grid households. A dedicated reactor design enabled on-demand dihydrogen generation, coupled with a Proton Exchange Membrane Fuel Cell (PEMFC) for electricity and heat production. Different energy management strategies were compared, highlighting the limitations of single-purpose approaches and the benefits of converting surplus electricity to heat. The integration of photovoltaic generation further reduced magnesium demand by 30%, thus reducing storage requirements to close to 1565 kg of magnesium powder per year, i.e., a volume of 0.9 m3 to cover the heat and electricity needs of a four-person household. Results demonstrate that combining water hydrolysis with magnesium and renewables provides a feasible and sustainable solution for autonomous energy supply in isolated sites.

Hydrogen doi: 10.3390/hydrogen6040116

Authors: Xinfeng Zhang Han Yue Hui Zheng Lixing Tan Zhiming Zhang Feng Li

Hydrogen energy is a pivotal alternative to lithium-ion batteries for low-altitude aircraft, offering a pathway to sustainable aviation with its zero emissions and high energy density. Nevertheless, its broader application is hindered by challenges in storage, safety, and performance under extreme conditions such as low pressure and low temperature at high altitudes. This paper systematically evaluates various hydrogen power technologies—including water-cooled and air-cooled proton exchange membrane fuel cells (PEMFCs) as well as hydrogen turbines—highlighting their respective advantages, limitations, and suitability for different aircraft types. Among these, water-cooled PEMFCs are identified as the most viable option for manned low-altitude aircraft due to their balanced performance in power density and startup capability. In contrast, air-cooled PEMFCs demonstrate distinct cost-effectiveness for lightweight drones, while hydrogen turbines show promise for long-range regional transport. Furthermore, we analyze current progress in integrating PEMFCs into aircraft platforms and discuss persistent challenges in system compatibility and environmental adaptation. Finally, potential future development directions for PEMFC applications in low-altitude aviation are outlined.

Hydrogen doi: 10.3390/hydrogen6040115

Authors: Igor Y. Shchapin Andrey I. Nekhaev

Molecular hydrogen is the basis of hydrogen energy. It is formed and used in many fields of industry, physics, and chemistry. Molecular hydrogen is the main product formed during the gamma radiolysis of liquid cyclohexane. When studying the mechanism of molecular hydrogen formation during the gamma radiolysis of liquid cyclohexane, we found that the values of adiabatic electron affinity, one of the fundamental characteristics of atoms and molecules, had not yet been experimentally determined for hydrogen and cyclohexane molecules. Theoretical estimates of the adiabatic electron affinity of the hydrogen molecule made by other authors varied widely ([−0.3; −5.771] eV) and could not be compared with experimental values due to the absence of such data. Using DFT calculations at the PBE0/TZVPP level of theory, and a constructed correlation with experimental values of the adiabatic first ionization potential and electron affinity for a number of molecules, neutral radicals, and atoms, we estimated, for the first time, the experimental adiabatic electron affinities of hydrogen (−3.08 eV) and cyclohexane (−2.13 eV) molecules in the gas phase. When an electron is attached to a cyclohexane molecule, a cyclohexane radical anion is formed, a new, highly reactive species that has not been studied before. A new perspective on molecular hydrogen formation during the gamma radiolysis of liquid cyclohexane was introduced and discussed.

Hydrogen doi: 10.3390/hydrogen6040114

Authors: Seyedehfaranak Hosseinigourajoubi Chris Schade Jacques Huot

In this paper, we report the effects of cold rolling, ball milling, and cold pressing on the first hydrogenation behavior of Ti0.488Fe0.460Mn0.052 alloy synthesized by gas atomization and exposed to the air for an extended period. It was found that cold pressing led to a higher hydrogen absorption capacity of 1.9 wt.%, while ball milling significantly improved the kinetics, achieving an incubation time of only 7 min. The cold-rolled sample (5 passes) showed a hydrogen absorption capacity similar to the ball-milled sample (1.5 wt.%) but with a slower hydrogenation rate. To further optimize the cold rolling process, the influence of the rolling atmosphere and the number of passes was systematically examined. In both air and argon, increasing the number of cold rolling passes resulted in longer incubation times. However, samples rolled under argon showed shorter incubation times compared to those rolled in the air. The difference between the two atmospheres became more pronounced after 20 rolling passes; the sample rolled in argon showed an incubation time of 55 min, whereas the sample rolled in air failed to absorb hydrogen even after 24 h.

Hydrogen doi: 10.3390/hydrogen6040113

Authors: Elitsa Petkucheva Jordan Iliev Galin Borisov Evelina Slavcheva

This work demonstrates for the first time a cost-effective modification of stainless-steel electrodes with an Fe3+ precursor via the deep-and-dry method (DDM) at processing temperatures between 20 °C and 80 °C, enabling their simultaneous applicability for both OER and HER in zero-gap electrolyzers. The approach offers a durable and economical alternative to conventional nickel-based electrodes. Morphological and compositional analyses by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) demonstrated a pronounced temperature-dependent evolution of surface features. At 20 °C, the coatings exhibited high porosity and incomplete coverage, whereas treatment at 60 °C yielded a compact, uniform, and continuous layer with suppressed Fe/Ni exposure and enhanced oxygen incorporation. Electrochemical characterization in 25% KOH by cyclic voltammetry and polarization measurements confirmed reversible redox behavior and comparable electrochemically active surface areas across all samples, with the 60 °C electrodes achieving the highest catalytic activity. In electrolysis cell tests (zero gap), the optimized electrodes delivered low cell voltages, current densities up to 1.35 A cm−2, and power outputs approaching 3.5 W cm−2. These results establish processing temperature as a decisive factor for tailoring the morphology, composition, and performance of DDM-fabricated electrodes, underscoring the promise of 60 °C-treated electrodes for efficient hydrogen production.

Hydrogen doi: 10.3390/hydrogen6040112

Authors: Alessandro Franco Michele Rocca

The integration of renewable energy sources, particularly photovoltaic (PV) solar, is increasingly challenged by the limited flexibility and storage capacity of actual energy systems. Hydrogen produced via renewable-powered electrolysis offers a promising pathway to address these constraints. This paper explores hydrogen blending into the natural gas grid as a systemic solution to enhance power system flexibility and support renewable (PV) expansion. Methodologically, the analysis is based on actual grid flow dynamics rather than static averages, identifying network nodes with stable gas demand as the most suitable for hydrogen injection. The novelty of this study lies in framing power-to-gas coupling as an operational flexibility tool rather than a storage-only option, and in quantifying its potential contribution to PV deployment. The methodology is applied to the Italian energy system, chosen as a representative case of high PV penetration and gas dependency. Analysis indicates that under current regulatory constraints (up to 5% hydrogen blending), the additional PV capacity that could be effectively integrated remains limited, resulting in modest reductions in natural gas consumption (<1%) and CO2 emissions (~0.3%). However, the approach demonstrates the conceptual and methodological relevance of treating gas networks as dynamic elements of an integrated power-to-gas system. Hydrogen blending thus emerges as a transitional but essential step toward future multi-energy integration under evolving regulatory and economic frameworks.

Hydrogen doi: 10.3390/hydrogen6040111

Authors: Rocio Maceiras Victor Alfonsin Jorge Feijoo Leticia Perez-Rial Adrian Lopez-Granados

As hydrogen emerges as a key vector in the shift toward cleaner energy systems, the evaluation of storage technologies becomes essential to support its integration across diverse applications. This work provides a comparative analysis of four hydrogen storage methods, compressed gas, metal hydrides, metal–organic frameworks (MOFs), and carbon-based materials, using a structured multi-criteria decision-making (MCDM) approach, specifically the Analytic Hierarchy Process (AHP) and Technique for Order Preference by Similarity to Ideal Solution (TOPSIS). The evaluation is based on a comprehensive set of technical, economic, and environmental criteria, including safety, storage capacity, efficiency, cycle durability, technological maturity, environmental impact, cost, and scalability. The analysis adopts a technology-oriented perspective, focusing on the intrinsic performance and feasibility of hydrogen storage systems rather than on a detailed techno-economic optimization. The results show that metal hydrides offer the most balanced performance, driven by high volumetric capacity and solid-phase stability, followed closely by compressed hydrogen, which stands out for its technological maturity and well-established infrastructure, despite facing significant challenges related to safety and space efficiency due to high-pressure storage requirements. Carbon-based materials and MOFs, although promising in specific aspects such as safety, storage density, or material sustainability, are hindered by technological immaturity and operational limitations.

Hydrogen doi: 10.3390/hydrogen6040110

Authors: Konstantina Vogiatzaki Giovanni Tretola Laurie Cesmat

The global transition toward low-carbon energy and transportation systems positions hydrogen as a key clean and versatile energy carrier. However, ensuring the safe handling and storage of hydrogen—particularly in its liquid form LH2)—remains a critical challenge to large-scale deployment. Accidental releases of LH2 can lead to rapid dispersion, cryogenic hazards, and increased risks of ignition or detonation due to hydrogen’s low ignition energy and wide flammability limits. This review synthesizes recent advances in the understanding and modelling of LH2 safety scenarios, emphasizing the complementary roles of Computational Fluid Dynamics (CFD) and Machine Learning (ML). The paper first outlines the fundamental physical processes governing cryogenic hydrogen leaks, spills, and jet releases, followed by an overview of current storage and sensing technologies. Special consideration is given to safety implications arising from the differences between open and enclosed environments and the fact that existent sensing technologies present deficiencies at low temperatures. CFD-based studies are reviewed to illustrate how these methods capture complex flow and dispersion dynamics under diverse operational and environmental conditions, supported by a summary of existing experimental investigations used for model validation. The emerging role of ML is then examined, focusing on its integration with CFD simulations and sensor networks for predictive risk assessment, real-time leak detection, and the development of digital twins. Finally, integrated CFD–ML-sensor systems are discussed as a pathway toward a physics-informed, data-driven framework for advancing hydrogen safety and reliability.

Hydrogen doi: 10.3390/hydrogen6040109

Authors: Leo Jansons Andris Backurs Laila Zemite Namejs Zeltins Aigars Laizans

This study evaluates the technical, design, and economic feasibility of large-scale hydrogen storage in deep water-bearing geological formations (aquifers), presenting it as a scalable solution for seasonal energy storage within the European Union’s decarbonization framework. A techno-economic model was developed for a 1 BCM facility, integrating geomechanical, microbial, and thermodynamic criteria. The results indicate a recoverable hydrogen fraction of 70–85%, with dissolution and microbial conversion losses limited to below 10% under optimized operational regimes. Geochemical and microbiological modelling demonstrated that sulfate-reducing and methanogenic bacterial activity can be reduced by 80–90% through controlled salinity and pH management. The proposed design, incorporating high-permeability sandstone reservoirs (100–300 mD), hydrogen-resistant materials, and fibre-optic monitoring ensures stable containment at 60–100 bar pressure and enables multi-cycle operation with minimal leakage (<0.05% per year). Economically, the baseline Levelized Cost of Hydrogen Storage (LCOHS) for aquifers was found to be ~0.29 EUR/kWh, with potential reductions to ~0.18 EUR/kWh through optimized drilling, modularized compression systems, and microbial mitigation. The lifecycle carbon footprint (0.20–0.36 kg CO2-eq/kg H2) is competitive with other geological storage methods, while offering superior scalability and strategic flexibility.

Hydrogen doi: 10.3390/hydrogen6040108

Authors: Arman Z. Miniyazov Nuriya M. Mukhamedova Igor A. Sokolov Timur R. Tulenbergenov Zhanna N. Ospanova Gulzhaz K. Uazyrkhanova Balzhan Y. Bekmagambetova Ospan Oken Riza Y. Zhakiya

A comprehensive study of the structural–phase transformations and hydrogen desorption kinetics in the Mg56Al44 system was conducted using a multistage approach combining thermodynamic modeling CALPHAD, Thermo-Calc 2025a, mechanical synthesis (MS), spark plasma sintering (SPS), and subsequent dispersion treatment. Thermodynamic modeling revealed a stable existence region of the intermetallic compound Mg17Al12, exhibiting Cp-T anomalies at 303 and 351 °C that closely corresponded to the experimental DSC/TGA results. Microstructural analysis showed that varying the ball-to-powder ratio BPR 20:1 and BPR 30:1 determines the defect density, crystallite size 25–45 nm, and lattice strain 1.5–3.0 × 10−3, all of which directly influence the hydrogen desorption kinetics. For the samples synthesized at BPR 30:1, the onset temperature of hydrogen release decreased to 180–200 °C while maintaining a hydrogen storage capacity of 4.9 wt.%, accompanied by a reduction in the apparent activation energy of desorption from 92 to 74 kJ·mol−1 according to the Kissinger method. The dispersion stage partially disrupted and redistributed the surface MgO layer, leading to a reduction in its overall contribution and improvement in structural homogeneity, rather than complete oxide removal. The combined MS-SPS-dispersion processing route enabled controlled nanostructure formation, reduced the hydrogen desorption temperature by approximately 100 °C compared to conventional MgH2-based materials, and significantly enhanced the thermokinetic performance. These findings demonstrate that Mg-Al alloys are promising candidates for solid-state hydrogen storage systems with improved desorption kinetics and reduced activation barriers.

Hydrogen doi: 10.3390/hydrogen6040107

Authors: Yang Li Shourui Zhang Meng Yu Yang Wu Jiake Wu Long Jiang

Hydrogen leakage is a critical safety concern for high-pressure storage systems, where orifice geometry significantly influences dispersion and risk. Previous studies on leakage and diffusion have mostly focused on closed or semi-closed environments, while thorough exploration has been conducted on open and unshielded environments. This work compares three typical orifice types—circular, slit, and Y-type—through controlled experiments. Results show that circular orifices generate directional jets with steep gradients but relatively low concentrations, with a 1 mm case reaching only 0.725% at the jet core. Slit orifices exhibit more uniform diffusion; at 1 mm, concentrations ranged from 2.125% to 2.625%. Y-type orifices presented the highest hazard, with 0.5 mm leaks producing 2.9% and 1 mm cases approaching the 4% lower flammability limit within 375 s. Equilibrium times increased with orifice size, from 400–800 s for circular and slit leaks to up to 900 s for Y-type leaks, some of which failed to stabilize. Response behavior also varied: Y-type leaks achieved rapid multi-point responses (as short as 10 s), while circular and slit leaks responded more slowly away from the jet core. Overall risk ranking was circular < slit < Y-type, underscoring the urgent need for geometry-specific monitoring strategies, sensor layouts, and emergency thresholds to ensure safe hydrogen storage.

Hydrogen doi: 10.3390/hydrogen6040106

Authors: Ayoub Koufi Younes Ziat Hamza Belkhanchi

This paper is based on the BoltzTrap package implemented in the Wien2k code to theoretically analyze and predict the structural, electronic, thermoelectric, and hydrogen storage properties of MgXH3 hydride perovskites (X = Cr, Mn, Fe, Co, Ni, and Cu). The study explores the dual functional potential of these compounds, highlighting how their hydrogen storage capability relates to their temperature-dependent thermoelectric performance. Analysis of band structures and densities of electronic states (DOS) reveals that all the compounds studied exhibit metallic behavior, characterized by an overlap between the valence band and the conduction band, indicating a zero electronic gap. Thermal properties show great variability depending on the transition metal involved. In particular, electrical conductivity and thermal conductivity evolve differently with temperature, directly influencing the figure of merit (Zt) of thermoelectric materials. The results suggest that although most MgXH3 compounds are not promising candidates for thermoelectric applications due to their high thermal conductivity and low density of states near the EF, MgNiH3 and MgCuH3 stand out with attractive thermoelectric potential. These properties make them attractive for energy conversion, waste heat recovery and solid-state cooling applications. This theoretical study highlights the potential of magnesium-based perovskite hydrides in energy conversion technologies, including thermoelectricity and hydrogen storage.

Hydrogen doi: 10.3390/hydrogen6040105

Authors: Maria Giovanna Buonomenna Aliaksei Patonia

As global efforts to decarbonize intensify, hydrogen produced via renewable electricity has emerged as a pivotal energy vector for a sustainable industrial future. This commentary provides a critical analysis of the current state of the hydrogen economy in Europe, detailing the core principles, operational mechanisms, and industrial status of four primary water electrolysis technologies: alkaline (ALK), proton exchange membrane (PEM), solid oxide (SOEC), and anion exchange membrane (AEM). Furthermore, it explores the significant socio-political challenges inherent in producing green hydrogen in non-EU nations for subsequent import into the European market.

Hydrogen doi: 10.3390/hydrogen6040104

Authors: Farhan Haider Joyo Daniele Groppi Lorenzo Villani Irfan Davide Astiaso Garcia

The iron and steel industry is one of the largest industrial sources of greenhouse gas emissions. This paper examines the potential of green hydrogen as a reducing agent for decarbonizing primary steel production, focusing on the Taranto integrated steelworks in southern Italy. Producing about 3.5 Mt of crude steel annually, the plant is also among the country’s biggest emitters, with CO2 emissions of roughly 8 Mt per year at typical blast furnace intensity (2.2 tCO2/t steel). The analysis quantifies the hydrogen demand required to replace fossil fuels in iron ore reduction and evaluates the techno-economic feasibility of meeting it with green hydrogen. Using DWSIM (open-source chemical process simulation software, v9.0.2) for water electrolysis powered by renewables, the study estimates both the CO2 emission reductions and cost impacts of hydrogen-based steelmaking. Results show that integrating green hydrogen at Taranto could achieve deep decarbonization by cutting emissions by over 90%, with a base-case levelized hydrogen cost (LCOH) of 3.6 EUR/kg and green steel production cost 653 EUR/t. With optimistic assumptions (renewable electricity at 40 EUR/MWh and electrolyzer CAPEX halved to 500 EUR/kW), hydrogen cost could be reduced to 2.3 EUR/kg, making green steel cost-competitive with conventional steel and implying a breakeven carbon price of under 60 EUR/t. Sensitivity analyses highlight that falling renewable electricity prices, supportive carbon policies, and successful demonstration projects are key enablers for economic viability. The findings underscore that renewable hydrogen can be a viable decarbonization pathway for steel when coupled with continued technological improvements and policy support.

Hydrogen doi: 10.3390/hydrogen6040103

Authors: Ayoub Boutaghane Mounir Aksas Djafar Chabane Nadhir Lebaal

Algeria’s transition toward sustainable energy requires the exploitation of its abundant solar and wind resources for green hydrogen production. This study assesses the techno-economic feasibility of an off-grid PV/wind hybrid system integrated with a hydrogen subsystem (electrolyzer, fuel cell, and hydrogen storage) to supply both electricity and hydrogen to decentralized sites in Algeria. Using HOMER Pro, five representative Algerian regions were analyzed, accounting for variations in solar irradiation, wind speed, and groundwater availability. A deferrable water-extraction and treatment load was incorporated to model the water requirements of the electrolyzer. In addition, a comprehensive sensitivity analysis was conducted on solar irradiation, wind speed, and the capital costs of PV panels and wind turbines to capture the effects of renewable resource and investment cost fluctuations. The results indicate significant regional variation, with the levelized cost of energy (LCOE) ranging from 0.514 to 0.868 $/kWh, the levelized cost of hydrogen (LCOH) between 8.31 and 12.4 $/kg, and the net present cost (NPC) between 10.28 M$ and 17.7 M$, demonstrating that all cost metrics are highly sensitive to these variations.

Hydrogen doi: 10.3390/hydrogen6040102

Authors: Mohamed-Amine Babay Mustapha Adar Mohamed El Messoussi Ahmed Chebak Mustapha Mabrouki

To simultaneously improve mass transfer and minimize pressure drop in proton exchange membrane fuel cells (PEMFCs), this study proposes a novel bionic flow field inspired by the streamlined abdominal structure of the peregrine falcon. A three-dimensional channel geometry is developed from this biological prototype and integrated into a single-channel PEMFC model for numerical simulation. A series of computational fluid dynamics (CFD) analyses compare the new design against conventional straight, trapezoidal, and sinusoidal flow fields. The results demonstrate that the falcon-inspired configuration enhances oxygen delivery, optimizes water management, and achieves a more uniform current density distribution. Remarkably, the design delivers a 9.45% increase in peak power density while significantly reducing pressure drop compared to the straight channel. These findings confirm that biologically optimized aerodynamic structures can provide tangible benefits in PEMFC flow field design by boosting electrochemical performance and lowering parasitic losses. Beyond fuel cells, this bio-inspired approach offers a transferable methodology for advanced energy conversion systems where efficient fluid transport is essential.

Hydrogen doi: 10.3390/hydrogen6040101

Authors: Hani Muhsen Rashed Tarawneh

While renewable energy deployment has accelerated in recent years, fossil fuels continue to play a dominant role in electricity generation worldwide. This necessitates the development of transitional strategies to mitigate greenhouse gas emissions from this sector while gradually reducing reliance on fossil fuels. This study investigates the potential of blending green hydrogen with natural gas as a transitional solution to decarbonize Jordan’s electricity sector. The research presents a comprehensive techno-economic and environmental assessment evaluating the compatibility of the Arab Gas Pipeline and major power plants with hydrogen–natural gas mixtures, considering blending limits, energy needs, environmental impacts, and economic feasibility under Jordan’s 2030 energy scenario. The findings reveal that hydrogen blending between 5 and 20 percent can be technically achieved without major infrastructure modifications. The total hydrogen demand is estimated at 24.75 million kilograms per year, with a reduction of 152.7 thousand tons of carbon dioxide per annum. This requires 296,980 cubic meters of water per year, equivalent to only 0.1 percent of the National Water Carrier’s capacity, indicating a negligible impact on national water resources. Although technically and environmentally feasible, the project remains economically constrained, requiring a carbon price of $1835.8 per ton of carbon dioxide for economic neutrality.

Hydrogen doi: 10.3390/hydrogen6040100

Authors: Edgar López-Martínez Samuel Eduardo Salud-Ordon Octavio Vázquez-Gómez Miguel Iván Dávila-Pérez Julio C. Villalobos Jesus Israel Barraza-Fierro

The effect of tempering temperature and tempering time on the density of hydrogen traps, hydrogen diffusivity, and microhardness in a vanadium-modified AISI 4140 martensitic steel was determined. Tempering parameters were selected to activate the second, third, and fourth tempering stages. These conditions were intended to promote specific microstructural transformations. Permeability tests were performed using the electrochemical method developed by Devanathan and Stachurski, and microhardness was measured before and after these tests. It was observed that hydrogen diffusivity is inversely proportional to microhardness, while the density of hydrogen traps is directly proportional to microhardness. The lowest hydrogen diffusivity, the highest trap density, and the highest microhardness were obtained in the as-quenched condition and the tempering at 286 °C for 0.25 h. In contrast, tempering at a temperature corresponding to the fourth tempering stage increases hydrogen diffusivity and decreases the density of hydrogen traps and microhardness. However, as the tempering time or temperature increases, the opposite occurs, which is attributed to the formation of alloy carbides. Finally, hydrogen has a softening effect for tempering temperatures corresponding to the fourth tempering stage, tempering times of 0.25 h, and in the as-quenched condition. However, with increasing tempering time, hydrogen has a hardening effect.

Hydrogen doi: 10.3390/hydrogen6040099

Authors: Lucimar Venancio Amaral Augusto César Teixeira Malaquias Gabriel Heleno de Paula Araújo Marcos de Carvalho Torres Filho Marco André Fraga Ricardo Belchior Torres Rita de Cássia de Oliveira Sebastião Fabricio José Pacheco Pujatti

This experimental study examines the effect of adding a hydrogen-enriched synthetic gaseous mixture (HGM’) on the combustion and fuel conversion efficiency of a single-cylinder research engine (SCRE). The work assesses the viability of using this mixture as a supplemental fuel for flex-fuel engines operating under urban driving cycling conditions. An SCRE, the AVL 5405 model, was employed, operating with ethanol and gasoline as primary fuels through direct injection (DI) and a volumetric compression ratio of 11.5:1. The HGM’ was added in the engine’s intake via fumigation (FS), with volumetric proportions ranging from 5% to 20%. The tests were executed at 1900 rpm and 2500 rpm engine speeds, with indicated mean effective pressures (IMEPs) of 3 and 5 bar. When HGM’s 5% v/v was applied at 2500 rpm, the mean indicated effective pressure of 3 bar was observed. A decrease of 21% and 16.5% in the ISFC was observed when using gasoline and ethanol as primary fuels, respectively. The usage of an HGM’ combined with gasoline or ethanol, proved to be a relevant and economically accessible strategy in the improvement of the conversion efficiency of combustion fuels, once this gaseous mixture could be obtained through the vapor-catalytic reforming of ethanol, giving up the use of turbochargers or lean and ultra-lean burn strategies. These results demonstrated the potential of using HGM’ as an effective alternative to increase the efficiency of flex-fuel engines.

Hydrogen doi: 10.3390/hydrogen6040098

Authors: Domenico Vizza Roberta Caponi Umberto Di Matteo Enrico Bocci

Driven by the growing availability of funding opportunities, electrolyzers have become increasingly accessible, unlocking significant potential for large-scale green hydrogen production. The goal of this investigation is to develop a techno-economic optimization framework for the design of a stand-alone photovoltaic (PV)-driven hydrogen production and refueling station, with the explicit objective of minimizing the levelized cost of hydrogen (LCOH). The system integrates PV generation, a proton-exchange-membrane electrolyzer, battery energy storage, compression, and high-pressure hydrogen storage to meet the daily demand of a fleet of fuel cell buses. Results show that the optimal configuration achieves an LCOH of 11 €/kg when only fleet demand is considered, whereas if surplus hydrogen sales are accounted for, the LCOH reduces to 7.98 €/kg. The analysis highlights that more than 75% of total investment costs are attributable to PV and electrolysis, underscoring the importance of capital incentives. Financial modeling indicates that a subsidy of about 58.4% of initial CAPEX is required to ensure a 10% internal rate of return under EU market conditions. The proposed methodology provides a reproducible decision-support tool for optimizing off-grid hydrogen refueling infrastructure and assessing policy instruments to accelerate hydrogen adoption in heavy-duty transport.

Hydrogen doi: 10.3390/hydrogen6040097

Authors: Kokoutse Gawou Obindah Gershon Joseph Kwasi Asafo Sonia Agbonjaru

The United Nations has set a global vision towards emissions reduction and green growth through the Sustainable Development Goals (SDGs). Towards the realisation of SDGS 7, 9, and 13, we focus on green hydrogen production as a potential pathway to achievement. Green hydrogen, produced via water electrolysis powered by renewable energy sources, represents a pivotal solution towards climate change mitigation. Energy access in West Africa remains a challenge, and dependency on fossil fuels persists. So, green hydrogen offers an opportunity to harness abundant solar resources, reduce carbon emissions, and foster economic development. This study evaluates the techno-economic feasibility of green hydrogen production in five West African countries: Ghana, Nigeria, Mali, Niger, and Senegal. The analyses cover the solar energy potential, hydrogen production capacities, and economic viability using the Levelised Cost of Hydrogen (LCOH) and Net Present Value (NPV). Results indicate substantial annual hydrogen production potential with LCOH values competitive with global benchmarks amidst the EU’s Carbon Border Adjustment Mechanism (CBAM). Despite this potential, several barriers exist, including high initial capital costs, policy and regulatory gaps, limited technical capacity, and water resource constraints. We recommend targeted strategies for strengthening policy frameworks, fostering international partnerships, enhancing regional infrastructure integration, and investing in capacity-building initiatives. By addressing these barriers, West Africa can be a key player in the global green hydrogen market.

Hydrogen doi: 10.3390/hydrogen6040096

Authors: Miguel Simão Coelho Pedro Jorge Coelho Ana Filipa Ferreira Elena Surra

Hydrogen plays a central role in ensuring the fulfillment of the climate and energy goals established in the Paris Agreement. To implement sustainable and resilient hydrogen economies, it is essential to analyze the entire hydrogen value chain, following a Life Cycle Assessment (LCA) methodology. To determine the current methodologies, approaches, and research tendencies adopted when performing LCA of hydrogen energy systems, a systematic literature analysis is carried out in the present study. The choices regarding the “goal and scope definition”, “life cycle inventory analysis”, and “life cycle impact assessment” in 70 scientific papers were assessed. Based on the collected information, it was concluded that there are no similar LCA studies, since specificities introduced in the system boundaries, functional unit, production, storage, transportation, end-use technologies, geographical specifications, and LCA methodological approaches, among others, introduce differences among studies. This lack of harmonization triggers the need to define harmonization protocols that allow for a fair comparison between studies; otherwise, the decision-making process in the hydrogen energy sector may be influenced by methodological choices. Although initial efforts have been made, their adoption remains limited, and greater promotion is needed to encourage wider implementation.

Hydrogen doi: 10.3390/hydrogen6040095

Authors: A. Ousegui B. Marcos

This study investigates hydrogen storage enhancement through adsorption in porous materials by coupling the Dubinin–Astakhov (D-A) adsorption model with H2 conservation equations (mass, momentum, and energy). The resulting system of partial differential equations (PDEs) was solved numerically using the finite element method (FEM). Experimental work using activated carbon as an adsorbent was carried out to validate the model. The comparison showed good agreement in terms of temperature distribution, average pressure of the system, and the amount of adsorbed hydrogen (H2). Further simulations with different adsorbents indicated that compact metal–organic framework 5 (MOF-5) is the most effective material in terms of H2 adsorption. Additionally, the pair (273 K, 800 s) remains the optimal combination of injection temperature and time. The findings underscore the prospective advantages of optimized MOF-5-based systems for enhanced hydrogen storage. These systems offer increased capacity and safety compared to traditional adsorbents. Subsequent research should investigate multi-objective optimization of material properties and system geometry, along with evaluating dynamic cycling performance in practical operating conditions. Additionally, experimental validation on MOF-5-based storage prototypes would further reinforce the model’s predictive capabilities for industrial applications.

Hydrogen doi: 10.3390/hydrogen6040094

Authors: Kubilay Bayramoğlu Tolga Bayramoğlu

The increasing global demand for clean energy highlights hydrogen as a strategic energy carrier due to its high energy density and carbon-free utilization. Currently, steam methane reforming (SMR) is the most widely applied method for hydrogen production; however, its high CO2 emissions undermine the environmental benefits of hydrogen. Blue hydrogen production integrates carbon capture and storage (CCS) technologies to overcome this drawback in the SMR process, significantly reducing greenhouse gas emissions. This study integrated a MATLAB-R2025b-based plug flow reactor (PFR) model for SMR kinetics with an Aspen HYSYS-based CCS system. The effects of reformer temperature (600–1000 °C) and steam-to-carbon (S/C) ratio (1–5) on hydrogen yield and CO2 emission intensity were investigated. Results show that hydrogen production increases with temperature, reaching maximum conversion at 850–1000 °C, while the optimum performance is achieved at S/C ratios of 2.5–3.0, balancing high hydrogen yield and minimized methane slip. Conventional SMR generates 9–12 kgCO2/kgH2 emissions, whereas SMR + CCS reduces this to 2–3 kgCO2/kgH2, achieving more than 75% reduction. The findings demonstrate that SMR + CCS integration effectively mitigates emissions and provides a sustainable bridging technology for blue hydrogen production, supporting the transition toward low-carbon energy systems.

Hydrogen doi: 10.3390/hydrogen6040093

Authors: Thomas Maugis Jérémy Ziliani Samuel Hibon Didier Chamagne David Bouquain

Shunting locomotives exhibit a wide and unpredictable range of power profiles. This unpredictability makes it impossible to rely on offline optimizations or predictive methods combined with online optimization. To maintain optimal performance across this broad range of operating conditions, the online control strategy must be robust. This article proposes a robust method to determine the optimal parameter combinations for an online energy management strategy of a hybrid fuel cell battery shunting locomotive, ensuring optimality across all scenario conditions. The first step involves extracting a statistically representative subspace for simulation, both in terms of parameter combinations and scenario conditions. A response surface model (numerical twin) is then constructed to extrapolate results across the entire space based on this simulated subspace. Using this model, the optimal solution is identified through metaheuristic algorithms (minimization search). Finally, the proposed solution is validated against a set of expert-defined scenarios. The result of the methodology ensures robust optimization across an infinite number of scenarios by minimizing the impact on both the fuel cell and the battery, without increasing mission costs.

Hydrogen doi: 10.3390/hydrogen6040092

Authors: Daisan Gopalasingam Bassam Rakhshani Cristina Rodriguez

Hydrogen propulsion technologies are emerging as a key enabler for decarbonizing the aviation sector, especially for regional commercial aircraft. The evolution of aircraft propulsion technologies in recent years raises the question of the feasibility of a hydrogen propulsion system for beyond regional aircraft. This paper presents a comprehensive review of hydrogen propulsion technologies, highlighting key advancements in component-level performance metrics. It further explores the technological transitions necessary to enable hydrogen-powered aircraft beyond the regional category. The feasibility assessment is based on key performance parameters, including power density, efficiency, emissions, and integration challenges, aligned with the targets set for 2035 and 2050. The adoption of hydrogen-electric powertrains for the efficient transition from KW to MW powertrains depends on transitions in fuel cell type, thermal management systems (TMS), lightweight electric machines and power electronics, and integrated cryogenic cooling architectures. While hydrogen combustion can leverage existing gas turbine architectures with relatively fewer integration challenges, it presents its technical hurdles, especially related to combustion dynamics, NOx emissions, and contrail formation. Advanced combustor designs, such as micromix, staged, and lean premixed systems, are being explored to mitigate these challenges. Finally, the integration of waste heat recovery technologies in the hydrogen propulsion system is discussed, demonstrating the potential to improve specific fuel consumption by up to 13%.