Hydrogen

34 pages, 3961 KiB

Open AccessArticle

Green Hydrogen and the Energy Transition: Hopes, Challenges, and Realistic Opportunities

by Alessandro Franco

Hydrogen 2025, 6(2), 28; https://doi.org/10.3390/hydrogen6020028 - 19 Apr 2025

This paper provides a system-level and dimensional analysis of green hydrogen, assessing its realistic deployment potential within broader energy transitions. While green hydrogen—produced via electrolysis using renewable electricity—is often promoted as a versatile decarbonization solution for industry, mobility, and civil applications, its practical [...] Read more.

This paper provides a system-level and dimensional analysis of green hydrogen, assessing its realistic deployment potential within broader energy transitions. While green hydrogen—produced via electrolysis using renewable electricity—is often promoted as a versatile decarbonization solution for industry, mobility, and civil applications, its practical implementation is constrained by high energy consumption, conversion inefficiencies, and complex supply chain requirements. This study highlights typical energy demands across key sectors and evaluates the scale of the renewable infrastructure needed to support them, offering quantitative insight into the feasibility of large-scale hydrogen integration. It also reflects current technological maturity, noting that many promising solutions remain far from industrial readiness. Finally, the paper underscores the importance of targeted policies and bankable investment models to foster the development of hydrogen ecosystems, emphasizing that its role should be framed within a selective, evidence-based strategy that focuses on high-impact applications. The analysis identifies key dimensional challenges, including the magnitude of renewable energy capacities required for sector-wide hydrogen integration and the scale of infrastructure investments needed to bridge current gaps. Full article

(This article belongs to the Special Issue Recent Advances in Hydrogen Technologies: Production, Storage and Utilization)

► Show Figures

Graphical abstract

17 pages, 5123 KiB

Open AccessArticle

Comparative Evaluation of Various ABO₃ Perovskites (A = La, Ca, Sr; B = Mn, Fe) as Oxygen Carrier Materials in Chemical Looping Hydrogen Production

by Antigoni Evdou and Vassilis Zaspalis

Hydrogen 2025, 6(2), 27; https://doi.org/10.3390/hydrogen6020027 - 17 Apr 2025

Abstract

This study comparatively evaluates the performance of ABO₃ perovskite materials (A = La, Ca, Sr; B = Mn, Fe) as oxygen carriers in three-step Chemical Looping Hydrogen (CLH) technology, focusing on redox behavior, oxygen transport capacity, hydrogen production, and selectivity under controlled [...] Read more.

This study comparatively evaluates the performance of ABO₃ perovskite materials (A = La, Ca, Sr; B = Mn, Fe) as oxygen carriers in three-step Chemical Looping Hydrogen (CLH) technology, focusing on redox behavior, oxygen transport capacity, hydrogen production, and selectivity under controlled pulse-mode conditions. The redox behavior of the materials is analyzed in relation to their defect chemistry. Perovskites such as (La_1−xCa_x)MnO₃, (La_1−xSr_x)MnO₃, and (La_0.6Ca_0.4)(Mn_1−xFe_x)O₃ were synthesized via wet chemical methods and tested in chemical looping cycles. Doping A-site cations with Ca or Sr enhanced oxygen delivery capacity by more than 100% upon reduction with CH₄ when dopant content (x) increased from 0 to 0.5. However, H₂ selectivity decreased from 52% to 2.5% for (La_1−xCa_x)MnO₃ and from 46% to 14% for (La_1−xSr_x)MnO₃ under the same conditions. In contrast, substituting Mn with Fe significantly improved hydrogen production, particularly in LaFeO₃, which exhibited the highest hydrogen selectivity and yield. At 1000 °C, LaFeO₃ produced nearly 10 mmol H₂ g⁻¹, with 80% generated during the reduction step at 99.9% selectivity and the remaining 20% during the water-splitting step at 100% selectivity. These results are linked to the extent of B-site cation reduction reactions (i) B⁴⁺ → B³⁺, which facilitates complete fuel oxidation and (ii) B³⁺ → B²⁺, which leads to partial fuel oxidation. The reverse of (ii) also contributes to H₂ production during water splitting. Additionally, the study assesses the materials’ microstructure and stability over prolonged cycles. The findings highlight Fe-based perovskites, particularly LaFeO₃, as promising candidates for CLH applications, emphasizing the need for structural and compositional optimization to enhance hydrogen production efficiency. Full article

► Show Figures

Figure 1

25 pages, 2422 KiB

Open AccessReview

An Overview of the Green Hydrogen Value Chain Technologies and Their Challenges for a Net-Zero Future

by Shahrouz Nayebossadri, Michael Walsh and Michael Smailes

Hydrogen 2025, 6(2), 26; https://doi.org/10.3390/hydrogen6020026 - 16 Apr 2025

Abstract

As hydrogen emerges as a pivotal energy carrier in the global transition towards net-zero emissions, addressing its technological and regulatory challenges is essential for large-scale deployment. The widespread adoption of hydrogen technologies requires extensive research, technical advancements, validation, testing, and certification to ensure [...] Read more.

As hydrogen emerges as a pivotal energy carrier in the global transition towards net-zero emissions, addressing its technological and regulatory challenges is essential for large-scale deployment. The widespread adoption of hydrogen technologies requires extensive research, technical advancements, validation, testing, and certification to ensure their efficiency, reliability, and safety across various applications, including industrial processes, power generation, and transportation. This study provides an overview of key enabling technologies for green hydrogen production and distribution, highlighting the critical challenges that must be overcome to facilitate their widespread adoption. It examines key hydrogen use cases across multiple sectors, analysing their associated technical and infrastructural challenges. The technological advancements required to improve hydrogen production, storage, transportation, and end-use applications are discussed. The development of state-of-the-art testing and validation facilities is also assessed, as these are vital for ensuring safety, performance, and regulatory compliance. This work also reviews some of the ongoing academic and industrial initiatives in the UK aimed at promoting technological innovation, advancing hydrogen expertise, and developing world-class testing infrastructures. This study emphasises the need for stronger, more integrated collaboration between universities, industries, and certifying bodies for building a strong network that promotes knowledge sharing, standardisation, and innovation for expanding hydrogen solutions and creating a sustainable hydrogen economy. Full article

► Show Figures

Graphical abstract

14 pages, 3882 KiB

Open AccessArticle

Acoustic Losses in Cryogenic Hydrogen at Transitions Between Tubes of Different Diameters

by Kian Conroy and Konstantin I. Matveev

Hydrogen 2025, 6(2), 25; https://doi.org/10.3390/hydrogen6020025 - 14 Apr 2025

Abstract

Acoustic oscillations in cryogenic systems can either be imposed intentionally, as in pulse-tube cryocoolers, or occur spontaneously due to Taconis-type thermoacoustic instabilities. To predict the propagation of sound waves in ducts with sudden changes in cross-sectional areas, minor losses associated with such transitions [...] Read more.

Acoustic oscillations in cryogenic systems can either be imposed intentionally, as in pulse-tube cryocoolers, or occur spontaneously due to Taconis-type thermoacoustic instabilities. To predict the propagation of sound waves in ducts with sudden changes in cross-sectional areas, minor losses associated with such transitions in oscillatory flows must be known. However, the current modeling approaches usually rely on correlations for minor loss coefficients obtained in steady flows, which may not accurately represent minor losses in sound waves. In this study, high-fidelity computational fluid dynamics simulations are undertaken for acoustic oscillations at transitions between tubes of different diameters filled with cryogenic hydrogen. The variable parameters include the tube diameter ratios, temperatures (80 K and 30 K), and acoustic impedances corresponding to standing and traveling waves. Computational simulation results are compared with reduced-order acoustic models to develop corrections for minor loss coefficients that describe transition losses in sound waves more precisely. The present findings can improve the accuracy of design calculations for acoustic cryocoolers and predictions of Taconis instabilities. Full article

► Show Figures

Figure 1

34 pages, 7136 KiB

Open AccessArticle

Comprehensive Study on Hydrogen Production for Sustainable Transportation Planning: Strategic, Techno-Economic, and Environmental Impacts

by Mohammadamin Ganji, Mohammad Gheibi, Alireza Aldaghi, Klodian Dhoska, Sonila Vito, Sina Atari and Reza Moezzi

Hydrogen 2025, 6(2), 24; https://doi.org/10.3390/hydrogen6020024 - 10 Apr 2025

Abstract

Hydrogen energy is essential in the transition to sustainable transportation planning, providing a clean and efficient alternative to traditional fossil fuels. As a versatile energy carrier, hydrogen facilitates the decarbonization of diverse transportation modes, including passenger vehicles, heavy-duty trucks, trains, and maritime vessels. [...] Read more.

Hydrogen energy is essential in the transition to sustainable transportation planning, providing a clean and efficient alternative to traditional fossil fuels. As a versatile energy carrier, hydrogen facilitates the decarbonization of diverse transportation modes, including passenger vehicles, heavy-duty trucks, trains, and maritime vessels. To justify and clarify the role of hydrogen energy in sustainable transportation planning, this study conducts a comprehensive techno-economic and environmental assessment of hydrogen production in the USA, Europe, and China. Utilizing the Shlaer–Mellor method for policy modeling, the analysis highlights regional differences and offers actionable insights to inform strategic decisions and policy frameworks for advancing hydrogen adoption. Hydrogen production potential was assessed from solar and biomass resources, with results showing that solar-based hydrogen production is significantly more efficient, producing 704 tons/yr/km², compared to 5.7 tons/yr/km² from biomass. A Monte Carlo simulation was conducted to project emissions and market share for hydrogen and gasoline vehicles from 2024 to 2050. The results indicate that hydrogen vehicles could achieve near-zero emissions and capture approximately 30% of the market by 2050, while gasoline vehicles will decline to a 60% market share with higher emissions. Furthermore, hydrogen production using solar energy in the USA yields a per capita output of 330,513 kg/yr, compared to 6079 kg/yr from biomass. The study concludes that hydrogen, particularly from renewable sources, holds significant potential for reducing greenhouse gas emissions, with policy frameworks in the USA, Europe, and China focused on addressing energy dependence, air pollution, and technological development in the transportation sector. Full article

► Show Figures

Figure 1

33 pages, 5847 KiB

Open AccessArticle

A Techno-Economic Assessment of Steam Methane Reforming and Alkaline Water Electrolysis for Hydrogen Production

by Ching Cheng Chu, Muhammad Danial Suhainin, Dk Nur Hayati Amali Pg Haji Omar Ali, Jia Yuan Lim, Poh Serng Swee, Jerick Yap Raymundo, Ryan Xin Han Tan, Mei Kei Yap, Hsin Fei Khoo, Hazwani Suhaimi and Pg Emeroylariffion Abas

Hydrogen 2025, 6(2), 23; https://doi.org/10.3390/hydrogen6020023 - 30 Mar 2025

Abstract

This study explores hydrogen’s potential as a sustainable energy source for Brunei, given the nation’s reliance on fossil fuels and associated environmental concerns. Specifically, it evaluates two hydrogen production technologies; steam methane reforming (SMR) and alkaline water electrolysis (AWE), through a techno-economic framework [...] Read more.

This study explores hydrogen’s potential as a sustainable energy source for Brunei, given the nation’s reliance on fossil fuels and associated environmental concerns. Specifically, it evaluates two hydrogen production technologies; steam methane reforming (SMR) and alkaline water electrolysis (AWE), through a techno-economic framework that assesses life cycle cost (LCC), efficiency, scalability, and environmental impact. SMR, the most widely used technique, is cost-effective but carbon-intensive, producing considerable carbon dioxide emissions unless combined with carbon capture to yield “blue hydrogen”. On the other hand, AWE, particularly when powered by renewable energy, offers a cleaner alternative despite challenges in efficiency and cost. The assessment revealed that AWE has a significantly higher LCC than SMR, making AWE the more economically viable hydrogen production method in the long term. A sensitivity analysis was also conducted to determine the main cost factors affecting the LCC, providing insights into the long term viability of each technology from an operational and financial standpoint. AWE’s economic viability is mostly driven by the high electricity and feedstock costs, while SMR relies heavily on feedstock costs. However, Environmental Impact Analysis (EIA) indicates that AWE produces significantly higher carbon dioxide emissions than SMR, which emits approximately 9100 metric tons of carbon dioxide annually. Nevertheless, findings suggest that AWE remains the more sustainable option due to its higher LCC costs and compatibility with renewable energy, especially in regions with access to low-cost renewable electricity. Full article

(This article belongs to the Special Issue Recent Advances in Hydrogen Technologies: Production, Storage and Utilization)

► Show Figures

Graphical abstract

17 pages, 4059 KiB

Open AccessArticle

Optimizing Hydrogen Storage and Fuel Cell Performance Using Carbon-Based Materials: Insights into Pressure and Surface Area Effects

by Ali Altuntepe, Selahattin Çelik and Recep Zan

Hydrogen 2025, 6(2), 22; https://doi.org/10.3390/hydrogen6020022 - 30 Mar 2025

Abstract

Efficient hydrogen storage is critical for advancing hydrogen-based technologies. This study investigates the effects of pressure and surface area on hydrogen storage in three carbon-based materials: graphite, graphene oxide, and reduced graphene oxide. Hydrogen adsorption–desorption experiments under pressures ranging from 1 to 9 [...] Read more.

Efficient hydrogen storage is critical for advancing hydrogen-based technologies. This study investigates the effects of pressure and surface area on hydrogen storage in three carbon-based materials: graphite, graphene oxide, and reduced graphene oxide. Hydrogen adsorption–desorption experiments under pressures ranging from 1 to 9 bar revealed nonlinear storage capacity responses, with optimal performance at around 5 bar. The specific surface area plays a pivotal role, with reduced graphene oxide and exhibiting a surface area of 70.31 m²/g, outperforming graphene oxide (33.75 m²/g) and graphite (7.27 m²/g). Reduced graphene oxide achieved the highest hydrogen storage capacity, with 768 sccm and a 3 wt.% increase over the other materials. In assessing proton-exchange fuel cell performance, this study found that increased hydrogen storage correlates with enhanced power density, with reduced graphene oxide reaching a maximum of 0.082 W/cm², compared to 0.071 W/cm² for graphite and 0.017 W/cm² for graphene oxide. However, desorption rates impose temporal constraints on fuel cell operation. These findings enhance our understanding of pressure–surface interactions and underscore the balance between hydrogen storage capacity, surface area, and practical performance in carbon-based materials, offering valuable insights for hydrogen storage and fuel cell applications. Full article

► Show Figures

Figure 1

32 pages, 5841 KiB

Open AccessReview

Computational Methods, Artificial Intelligence, Modeling, and Simulation Applications in Green Hydrogen Production Through Water Electrolysis: A Review

by Ahmed Y. Shash, Noha M. Abdeltawab, Doaa M. Hassan, Mohamed Darweesh and Y. G. Hegazy

Hydrogen 2025, 6(2), 21; https://doi.org/10.3390/hydrogen6020021 - 25 Mar 2025

Abstract

Green hydrogen production is emerging as a crucial component in global decarbonization efforts. This review focuses on the role of computational approaches and artificial intelligence (AI) in optimizing green hydrogen technologies. Key approaches to improving electrolyzer efficiency and scalability include computational fluid dynamics [...] Read more.

Green hydrogen production is emerging as a crucial component in global decarbonization efforts. This review focuses on the role of computational approaches and artificial intelligence (AI) in optimizing green hydrogen technologies. Key approaches to improving electrolyzer efficiency and scalability include computational fluid dynamics (CFD), thermodynamic modeling, and machine learning (ML). As an instance, CFD has achieved over 95% accuracy in estimating flow distribution and polarization curves, but AI-driven optimization can lower operational expenses by up to 24%. Proton exchange membrane electrolyzers achieve efficiencies of 65–82% at 70–90 °C, but solid oxide electrolyzers reach up to 90% efficiency at temperatures ranging from 650 to 1000 °C. According to studies, combining renewable energy with hydrogen production reduces emissions and improves grid reliability, with curtailment rates of less than 1% for biomass-driven systems. This integration of computational approaches and renewable energy ensures a long-term transition to green hydrogen while also addressing energy security and environmental concerns. Full article

► Show Figures

Graphical abstract

27 pages, 5910 KiB

Open AccessArticle

PEMFC Thermal Management Control Strategy Based on Dual Deep Deterministic Policy Gradient

by Zhi Zhang, Yunde Shen, Kai Ou, Zhuwei Liu and Dongji Xuan

Hydrogen 2025, 6(2), 20; https://doi.org/10.3390/hydrogen6020020 - 25 Mar 2025

Abstract

The operational performance of proton exchange membrane fuel cells (PEMFC) is highly influenced by temperature, making effective thermal management essential. However, the multivariate coupling between pumps and radiators presents significant control challenges. To address this issue, a dual DDPG-PID control strategy is proposed, [...] Read more.

The operational performance of proton exchange membrane fuel cells (PEMFC) is highly influenced by temperature, making effective thermal management essential. However, the multivariate coupling between pumps and radiators presents significant control challenges. To address this issue, a dual DDPG-PID control strategy is proposed, integrating temperature and flow rate variations to enhance system stability and response. Simulation results demonstrate that the proposed method significantly reduces temperature control errors and improves response time compared to conventional PID-based strategies. Specifically, the D-DDPG PID achieves a temperature error reduction of up to 75.4% and shortens the average tuning time by up to 25.6% compared to PSO-PID. Furthermore, the strategy optimizes cooling system performance, demonstrating its effectiveness in PEMFC thermal management. Full article

► Show Figures

Figure 1

10 pages, 1147 KiB

Open AccessPerspective

The Extractive Industry’s Decarbonization Potential Using Electrification and Hydrogen Technologies

by Antonis Peppas, Chrysa Politi and Maria Taxiarchou

Hydrogen 2025, 6(2), 19; https://doi.org/10.3390/hydrogen6020019 - 21 Mar 2025

Abstract

The challenge of achieving net-zero CO₂ emissions will require a significant scaling up of the production of several raw materials that are critical for decarbonizing the global economy. In contrast, metal extraction processes utilize carbon as a reducing agent, which is oxidized [...] Read more.

The challenge of achieving net-zero CO₂ emissions will require a significant scaling up of the production of several raw materials that are critical for decarbonizing the global economy. In contrast, metal extraction processes utilize carbon as a reducing agent, which is oxidized to CO₂, resulting in considerable emissions and having a negative impact on climate change. In order to abate their emissions, extractive industries will have to go through a profound transformation, including switching to alternative climate-neutral energy and feedstock sources. This paper presents the authors’ perspectives for consideration in relation to the H₂ potential for direct reduction of oxide and sulfide ores. For each case scenario, the reduction of CO₂ emissions is analyzed, and a breakthrough route for H₂S decomposition is presented, which is a by-product of the direct reduction of sulfide ores with H₂. Electrified indirect-fired metallurgical kiln advantages are also presented, a solution that can substitute fossil fuel-based heating technologies, which is one of the main backbones of industrial processes currently applied to the extractive industries. Full article

(This article belongs to the Special Issue Recent Advances in Hydrogen Technologies: Production, Storage and Utilization)

► Show Figures

Figure 1

19 pages, 6012 KiB

Open AccessArticle

Effect of Hydrogen Co-Firing with Natural Gas on Thermal Efficiency and CO₂ Emissions in Gas Turbine Power Plant

by Rizcky Rahadian Nugraha, S. Silviana and Widayat Widayat

Hydrogen 2025, 6(1), 18; https://doi.org/10.3390/hydrogen6010018 - 19 Mar 2025

Abstract

The Indonesian government has established an energy transition policy for decarbonization, including the target of utilizing hydrogen for power generation through a co-firing scheme. Several studies indicate that hydrogen co-firing in gas-fired power plants can reduce CO₂ emissions while improving efficiency. This [...] Read more.

The Indonesian government has established an energy transition policy for decarbonization, including the target of utilizing hydrogen for power generation through a co-firing scheme. Several studies indicate that hydrogen co-firing in gas-fired power plants can reduce CO₂ emissions while improving efficiency. This study develops a simulation model for hydrogen co-firing in an M701F gas turbine at the Cilegon power plant using Aspen HYSYS. The impact of different hydrogen volume fractions (5–30%) on thermal efficiency and CO₂ emissions is analyzed under varying operational loads (100%, 75%, and 50%). The simulation results show an increase in thermal efficiency with each 5% increment in the hydrogen fraction, averaging 0.32% at 100% load, 0.34% at 75% load, and 0.37% at 50% load. The hourly CO₂ emission rate decreased by an average of 2.16% across all operational load variations for every 5% increase in the hydrogen fraction. Meanwhile, the average reduction in CO₂ emission intensity at the 100%, 75%, and 50% operational loads was 0.017, 0.019, and 0.023 kg CO₂/kWh, respectively. Full article

► Show Figures

Figure 1

28 pages, 9044 KiB

Open AccessArticle

Strategies to Increase Hydrogen Energy Share of a Dual-Fuel Hydrogen–Kerosene Engine for Sustainable General Aviation

by Christian Reitmayr and Peter Hofmann

Hydrogen 2025, 6(1), 17; https://doi.org/10.3390/hydrogen6010017 - 19 Mar 2025

Abstract

Reducing CO₂ emissions in general aviation is a critical challenge, where battery electric and fuel cell technologies face limitations in energy density, cost, and robustness. As a result, hydrogen (H₂) dual-fuel combustion is a promising alternative, but its practical implementation [...] Read more.

Reducing CO₂ emissions in general aviation is a critical challenge, where battery electric and fuel cell technologies face limitations in energy density, cost, and robustness. As a result, hydrogen (H₂) dual-fuel combustion is a promising alternative, but its practical implementation is constrained by abnormal combustion phenomena such as knocking and pre-ignition, which limit the achievable H₂ energy share. In response to these challenges, this paper focuses on strategies to mitigate these irregular combustion phenomena while effectively increasing the H₂ energy share. Experimental evaluations were conducted on an engine test bench using a one-cylinder dual-fuel H₂ kerosene (Jet A-1) engine, utilizing two strategies, including water injection (WI) and rising the air–fuel ratio (AFR) by increasing the boost pressure. Additionally, crucial combustion characteristics and emissions are examined and discussed in detail, contributing to a comprehensive understanding of the outcomes. The results indicate that these strategies notably increase the maximal possible hydrogen energy share, with potential benefits for emissions reduction and efficiency improvement. Finally, through the use of 0D/1D simulations, this paper offers critical thermodynamic and efficiency loss analyses of the strategies, enhancing the understanding of their overall impact. Full article

► Show Figures

Figure 1

16 pages, 3460 KiB

Open AccessArticle

Relationship Between Area and Capacity of Hydrogen Refueling Stations and Derivation of Design Recommendations

by Armin Stein, Bastian Nolte, Umut Volkan Kizgin, Ole Grünewald, Güven Yurtseven and Thomas Vietor

Hydrogen 2025, 6(1), 16; https://doi.org/10.3390/hydrogen6010016 - 14 Mar 2025

Cited by 1

Abstract

Hydrogen plays a pivotal role in the decarbonization of the transport sector, necessitating the development of an adequate infrastructure in the form of hydrogen refueling stations (HRSs) to support hydrogen-powered vehicles. This study investigates the characteristics of hydrogen refueling stations to optimize their [...] Read more.

Hydrogen plays a pivotal role in the decarbonization of the transport sector, necessitating the development of an adequate infrastructure in the form of hydrogen refueling stations (HRSs) to support hydrogen-powered vehicles. This study investigates the characteristics of hydrogen refueling stations to optimize their spatial design and provide key performance indicators for spatial efficiency. An overview of HRS components and their operational requirements is provided, alongside the classification of stations into distinct categories. The primary focus is on analyzing the relationship between station area and capacity. Utilizing spatial data from hydrogen stations, areas are determined through Google Maps analysis. Linear and power regression models are applied to quantify the relationship, with both models proving effective for capturing these dynamics. Based on the findings, spatially efficient design recommendations are proposed, supplemented by examples and a conceptual blueprint for optimized HRS construction, which are then summarized in a morphological design catalog. Full article

► Show Figures

Figure 1

20 pages, 2224 KiB

Open AccessArticle

Sustainable Hydrogen Production from Plastic Waste: Optimizing Pyrolysis for a Circular Economy

by Fiyinfoluwa Joan Medaiyese, Hamid Reza Nasriani, Khalid Khan and Leila Khajenoori

Hydrogen 2025, 6(1), 15; https://doi.org/10.3390/hydrogen6010015 - 7 Mar 2025

Abstract

Hydrogen is a clean, non-polluting fuel and a key player in decarbonizing the energy sector. Interest in hydrogen production has grown due to climate change concerns and the need for sustainable alternatives. Despite advancements in waste-to-hydrogen technologies, the efficient conversion of mixed plastic [...] Read more.

Hydrogen is a clean, non-polluting fuel and a key player in decarbonizing the energy sector. Interest in hydrogen production has grown due to climate change concerns and the need for sustainable alternatives. Despite advancements in waste-to-hydrogen technologies, the efficient conversion of mixed plastic waste via an integrated thermochemical process remains insufficiently explored. This study introduces a novel multi-stage pyrolysis-reforming framework to maximize hydrogen yield from mixed plastic waste, including polyethylene (HDPE), polypropylene (PP), and polystyrene (PS). Hydrogen yield optimization is achieved through the integration of two water–gas shift reactors and a pressure swing adsorption unit, enabling hydrogen production rates of up to 31.85 kmol/h (64.21 kg/h) from 300 kg/h of mixed plastic wastes, consisting of 100 kg/h each of HDPE, PP, and PS. Key process parameters were evaluated, revealing that increasing reforming temperature from 500 °C to 1000 °C boosts hydrogen yield by 83.53%, although gains beyond 700 °C are minimal. Higher reforming pressures reduce hydrogen and carbon monoxide yields, while a steam-to-plastic ratio of two enhances production efficiency. This work highlights a novel, scalable, and thermochemically efficient strategy for valorizing mixed plastic waste into hydrogen, contributing to circular economy goals and sustainable energy transition. Full article

► Show Figures

Figure 1

12 pages, 3077 KiB

Open AccessArticle

Electrochemical Hydrogen Pump/Compressor in Single- and Double-Stage Regime

by Galin Borisov, Nevelin Borisov and Evelina Slavcheva

Hydrogen 2025, 6(1), 14; https://doi.org/10.3390/hydrogen6010014 - 6 Mar 2025

Abstract

This study presents the integration and evaluation of commercially available gas diffusion electrodes (GDEs), specifically designed for high-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs) within membrane electrode assemblies (MEA) for electrochemical hydrogen pump/compressor applications (EHP/C). Using Nafion 117 as a solid polymer electrolyte, [...] Read more.

This study presents the integration and evaluation of commercially available gas diffusion electrodes (GDEs), specifically designed for high-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs) within membrane electrode assemblies (MEA) for electrochemical hydrogen pump/compressor applications (EHP/C). Using Nafion 117 as a solid polymer electrolyte, the MEAs were analyzed for cell efficiency, hydrogen evolution, and hydrogen oxidation reactions (HER and HOR) under differential pressure up to 16 bar and a temperature ranging from 20 °C to 60 °C. Key properties of the GDEs, such as electrode thickness and conductivity, were investigated. The catalytic layer was characterized via XRD and EDX analyses to assess its surface and bulk composition. Additionally, the effects of increasing MEA’s geometric size (from 1 cm² to 5 cm²) and hydrogen crossover phenomena on the efficiency were examined in a single-cell setup. Electrochemical performance tests conducted in a single electrochemical hydrogen pump/compressor cell under hydrogen flow rates from 36.6 Ml·min⁻¹·cm⁻² to 51.3 mL·min⁻¹ cm⁻² at atmospheric pressure provided insights into the optimal operational parameters. For a double-stage application, the MEAs demonstrated enhanced current densities, achieving up to 0.6 A·cm⁻² at room temperature with further increases to 1 A·cm⁻² at elevated temperatures. These results corroborated the single-cell data, highlighting potential improvements in system efficiency and a reduction in adverse effects. The work underscores the potential of HT-PEMFC-based GDEs for the integration of MEAs applicable to advanced hydrogen compression technologies. Full article

► Show Figures

Figure 1

13 pages, 311 KiB

Open AccessArticle

Analysis Between Green Hydrogen and Other Financial Assets: A Multi-Scale Correlation Approach

by Eder J. A. L. Pereira, Letícia S. Anjos, Paulo Ferreira, Derick Quintino, Gerhard Ett and Thiago B. Murari

Hydrogen 2025, 6(1), 13; https://doi.org/10.3390/hydrogen6010013 - 28 Feb 2025

Abstract

Improvements in quality of life, new technologies and population growth have significantly increased energy consumption in Brazil and around the world. The Paris Agreement aims to limit global warming and promote sustainable development, making green hydrogen a fundamental option for industrial decarbonization. Green [...] Read more.

Improvements in quality of life, new technologies and population growth have significantly increased energy consumption in Brazil and around the world. The Paris Agreement aims to limit global warming and promote sustainable development, making green hydrogen a fundamental option for industrial decarbonization. Green hydrogen, produced through the electrolysis of water using renewable energy, is gaining traction as a solution to reducing carbon emissions, with the global hydrogen market expected to grow substantially. This study applies the

ρ_{D C C A}

method to evaluate the cross-correlation between the green hydrogen market and various financial assets, including the URTH ETF, Bitcoin, oil futures, and commodities, revealing some strong positive correlations. It highlights the interconnection of the green hydrogen market with developed financial markets and digital currencies. The cross-correlation between the green hydrogen market and the index representing global financial markets presented a value close to 0.7 for small and large time scales, indicating a strong cross-correlation. The green hydrogen market and Bitcoin also presented a cross-correlation value of 0.4. This study provides valuable information for investors and policymakers, especially those concerned with achieving sustainability goals and environmental-social governance compliance and seeking green assets to protect and diversify various traditional investments. Full article

► Show Figures

Figure 1

22 pages, 2692 KiB

Open AccessArticle

Life Cycle Greenhouse Gas Emissions Analysis of the Chlor-Alkali Process and By-Product Hydrogen in the United States

by Pradeep Vyawahare, Pingping Sun, Ben Young, Adarsh Bafana, Taemin Kim, Troy R. Hawkins and Amgad Elgowainy

Hydrogen 2025, 6(1), 12; https://doi.org/10.3390/hydrogen6010012 - 28 Feb 2025

Abstract

Hydrogen is considered a key energy carrier for which interest has grown over recent years. Chlor-alkali plants in the United States (U.S.) can potentially recover and supply the by-product hydrogen at scale. However, there is a scarcity of standard analysis for energy use [...] Read more.

Hydrogen is considered a key energy carrier for which interest has grown over recent years. Chlor-alkali plants in the United States (U.S.) can potentially recover and supply the by-product hydrogen at scale. However, there is a scarcity of standard analysis for energy use and emissions associated with products from chlor-alkali plants owing to lack of data and variations in chlor-alkali plant technology and operation. A rigorous life cycle analysis (LCA) is needed to quantify the emissions of by-product hydrogen and other products from chlor-alkali plants. In this study, we performed well-to-gate (WTG) emissions analysis of chlor-alkali products based on U.S. plant operating data gathered from the U.S. Environmental Protection Agency’s (EPA’s) Chemical Data Reporting database, the U.S. Energy Information Administration survey EIA-923 form, and the EPA’s Greenhouse Gas Reporting Program. We performed process-level mass allocation to allocate energy use and emissions to the chlor-alkali products. This study shows that the by-product hydrogen has WTG CO₂ emissions of 1.3–1.9 kgCO₂/kg H₂ for plants without combined heat and power (non-CHP) and 1.5–2.4 kgCO₂/kg H₂ for plants with combined heat and power (CHP). Furthermore, we identified that electricity upstream emissions are the key driver affecting the emissions of by-product hydrogen from non-CHP plants, while CHP emissions can be reduced by electricity export to grids with higher carbon intensity (CI). Finally, the study shows that chlor-alkali plants in the U.S. can potentially meet up to 320 kilotons of hydrogen demand (approximately 3% of total demand) annually. Full article

► Show Figures

Figure 1

22 pages, 1480 KiB

Open AccessArticle

Feasibility of Retrofitting a Conventional Vessel with Hydrogen Power Systems: A Case Study in Australia

by Muhammad Waris Yaar Khan and Hongjun Fan

Hydrogen 2025, 6(1), 11; https://doi.org/10.3390/hydrogen6010011 - 28 Feb 2025

Abstract

As the pursuit of greener energy solutions continues, industries worldwide are turning away from fossil fuels and exploring the development of sustainable alternatives to meet their energy requirements. As a signatory to the Paris Agreement, Australia has committed to reducing greenhouse gas emission [...] Read more.

As the pursuit of greener energy solutions continues, industries worldwide are turning away from fossil fuels and exploring the development of sustainable alternatives to meet their energy requirements. As a signatory to the Paris Agreement, Australia has committed to reducing greenhouse gas emission by 43% by 2030 and reaching net-zero emissions by 2050. Australia’s domestic maritime sector should align with these targets. This paper aims to contribute to ongoing efforts to achieve these goals by examining the technical and commercial considerations involved in retrofitting conventional vessels with hydrogen power. This includes, but is not limited to, an analysis of cost, risk, and performance, and compliance with classification society rules, international codes, and Australian regulations. This study was conducted using a small domestic commercial vessel as a reference to explore the feasibility of implementation of hydrogen-fuelled vessels (HFVs) across Australia. The findings indicate that Australia’s existing hydrogen infrastructure requires significant development for HFVs to meet the cost, risk, and performance benchmarks of conventional vessels. The case study identifies key determining factors for feasible hydrogen retrofitting and provides recommendations for the success criteria. Full article

► Show Figures

Figure 1

24 pages, 3772 KiB

Open AccessArticle

Application of Levelized and Environmental Cost Accounting Techniques to Demonstrate the Feasibility of Green Hydrogen-Powered Buses in Brazil

by Murilo L. Alcantara, José C. C. Santana, Cláudio A. O. Nascimento and Celma O. Ribeiro

Hydrogen 2025, 6(1), 10; https://doi.org/10.3390/hydrogen6010010 - 21 Feb 2025

Abstract

Background: This study applied levelized cost of hydrogen (LCOH) and environmental cost accounting techniques to evaluate the feasibility of producing green hydrogen (GH₂) via alkaline electrolysis for use in a bus fleet in Fortaleza, Brazil. Methods: A GH₂ plant with [...] Read more.

Background: This study applied levelized cost of hydrogen (LCOH) and environmental cost accounting techniques to evaluate the feasibility of producing green hydrogen (GH₂) via alkaline electrolysis for use in a bus fleet in Fortaleza, Brazil. Methods: A GH₂ plant with a 3 MW wind tower was considered in this financial project. A sensitivity analysis was conducted to assess the economic viability of the project, considering the influence of production volume, the number of electrolysis kits, financing time, and other kay economic indices. Revenue was derived from the sale of by-products, including green hospital oxygen (GHO₂) and excess wind energy. A life cycle assessment (LCA) was performed to quantify material and emission flows throughout the H₂ production chain. A zero-net hydrogen price scenario was tested to evaluate the feasibility of its use in urban transportation. Results: The production of GH₂ in Brazil using alkaline electrolysis powered by wind energy proved to be economically viable for fueling a hydrogen-powered bus fleet. For production volumes ranging from 8.89 to 88.9 kg H₂/h, the sensitivity analysis revealed high economic performance, achieving a net present value (NPV) between USD 19.4 million and USD 21.8 million, a payback period of 1–4 years, an internal rate of return (IRR) of 24–90%, and a return on investment (ROI) of 300–1400%. The LCOH decreased with increased production, ranging from 56 to 25 USD/MWh. Over the project timeline, GH₂ production and use in the bus fleet reduced CO₂ emissions by 53,000–287,000 t CO₂ eq. The fuel cell bus fleet project demonstrated viability through fuel cost savings and revenue from carbon credit sales, highlighting the economic, social, and environmental sustainability of GH₂ use in urban transportation in Brazil. Full article

► Show Figures

Figure 1

Journal Description

Hydrogen

Latest Articles

Journal Menu

Journal Browser

Highly Accessed Articles

Latest Books

E-Mail Alert

News

Topics

Conferences

Special Issues

Further Information

Guidelines

MDPI Initiatives

Follow MDPI