Hydrogen, Volume 7, Issue 3 (September 2026) – 44 articles

The World Bank’s Lighthouse Strategy identifies Morocco as a first mover exporter of green hydrogen and its derivatives to Europe; however, the engineering feasibility of the associated transport and storage network has not been quantitatively demonstrated. This study addresses that gap through an integrated spatial and multiperiod optimization framework that couples a spatially explicit Mixed Integer Linear Programming (MILP) model with a FlexSim/FloWorks digital twin for discrete event and hydraulic simulation. The MILP simultaneously optimizes electrolysis deployment, hydrogen storage technologies, and multimodal transport across a four node Moroccan export corridor (TanTan, Mohammedia, Jorf Lasfar, and Tanger Med) for the 2030, 2040, and 2050 planning horizons under a net present value objective. The optimal configuration combines a dedicated hydrogen backbone pipeline for the high volume production corridor with shortsea cabotage for the distribution branches, achieving a full chain levelized cost of ammonia (LCOA) of 1176 USD/t, consistent with the World Bank benchmark and reducing costs by 57 USD/t compared with an all cabotage configuration. The optimal network remains robust over a wide range of capital cost and financing assumptions, while the digital twin confirms the hydraulic and operational feasibility of the integrated pipeline–shipping system without critical port congestion. These findings demonstrate that combining optimization with digital twin validation provides a robust engineering basis for planning Morocco’s green hydrogen export infrastructure and supports investment decisions aligned with future CBAM compliant hydrogen and ammonia supply chains. Full article

Green hydrogen production through water electrolysis is a key pathway to the decarbonization of future energy systems. However, part of the electrical input is transformed into waste heat. In this study, alkaline, proton-exchange membrane, anion-exchange membrane, and solid oxide electrolysis systems are compared in terms of operating temperature, heat generation, heat transfer medium, and integration constraints. Reported COP values for commercial high-temperature vapour-compression heat pumps range from 2.4 to 5.8, depending on operating conditions. The heat-pump technologies reviewed include vapour-compression systems with single-stage, multistage, cascade, and transcritical configurations, together with absorption and adsorption systems, with a focus on suitable working fluids and practical limitations. The review distinguishes between direct heat recovery and heat recovery assisted by heat pumps, and it identifies two main areas of application: external supply for district heating, industrial consumers, and energy communities; and internal support for feedwater preheating, water cycle integration, and steam generation. A selection framework is proposed in which source- and sink-temperature compatibility determines thermodynamic feasibility, COP characterizes heat-pump performance, and LCoH supports techno-economic comparison. Direct heat recovery should be preferred when temperatures are compatible, while heat pumps can operate as enabling technologies when temperature upgrading is required and system-level economic and environmental performance remains advantageous. Full article

Hydrogen (H₂) is a common product of carbohydrate fermentation by the intestinal microbiota, transferred to the blood along the pressure gradient, and exhaled. As H₂ is not produced or metabolized in human cells, alveolar H₂ is distributed throughout the human body, including cellular organelles such as mitochondria, owing to systemic circulation and gas exchange. The electron transport chain comprises a series of oxidation–reduction (redox) enzymes in the mitochondria of human cells that facilitate adenosine triphosphate (ATP) synthesis. The catalytic activity of electron-transport enzymes is optimized at certain electrochemical potentials, as is hydrogen ion activity (pH). However, the human body is an aqueous system that must be electrically neutral. Membrane potentials exist between the interior and exterior of human cells because of the unequal distribution of ions across the membrane. The single-electrode potential can only be assessed relative to that of another electrode (i.e., a reference electrode). The electrochemical potentials relative to a standard hydrogen electrode (SHE) were measured; it was found that H₂ partial pressure was a fundamental factor that affected the SHE, pH, and the reversible hydrogen electrode. The H₂ partial pressure is not a unit used to characterize the human body; therefore, breath H₂ is an external variable in the redox environment in the human body. Full article

Microwave-driven thermochemical cycles can split water for hydrogen production at temperatures far below those of conventional solar thermochemical routes, yet the responsible physical mechanisms remain unclear and numerical models for the coupled solar-microwave hybrid system are still scarce. Building on previous experimental work, we developed a coupled numerical model that integrates impedance matching, non-thermal enhancement, two-stage Arrhenius kinetics, and energy conservation to systematically investigate the interplay between microwave power, temperature evolution, and reaction progress. The model predictions agree well with experimental data in terms of temperature evolution trends, power threshold ranges, and reaction timescales. The results indicate that, within the present modeling framework, the effective microwave absorption efficiency increases from 1.2% at low temperatures to approximately 14% near 85 °C, with the non-thermal enhancement factor contributing as an empirical parameter. Under pure microwave mode, the required power threshold for reaction initiation is approximately 120 W; the solar-microwave synergistic mode reduces this threshold to about 70 W, a 42% reduction. At an input power of 100 W, the energy conversion efficiency reaches a maximum of 42%. Analysis of the sudden temperature change identifies 85 °C as the critical triggering temperature: below it, the system remains in a low-absorption cold state, while once crossed, a positive feedback mechanism rapidly propels the system into the high-temperature reaction regime. This study provides a numerical modeling framework for describing the coupled solar-microwave thermal behavior of the system and for guiding the optimization of its operational parameters. Since the available measurements cannot independently separate the thermal and non-thermal contributions, the non-thermal enhancement remains an empirically introduced factor rather than an experimentally established physical effect. Full article

Hydrogen appears in almost every maritime decarbonization roadmap, yet it barely sails: 19 vessels against more than 1600 powered by liquefied natural gas. This study combines an analysis of the global alternative-fueled fleet and orderbook (3094 fuel-vessel records) with an assessment of 26 international and European governance units, two of which are documented absences of an instrument, grouped into the seven conditions a hydrogen vessel needs to be built, certified, crewed, insured, financed and refueled. None of the 26 fully covers the condition it addresses, and the deficits run across all seven domains. Nor does binding demand regulation reach hydrogen where it is currently viable: the tonnage threshold it applies makes eligible nine out of ten LNG or methanol vessels and only two out of ten hydrogen vessels, a difference that narrows but does not close once adjusted for vessel segment. We term this pattern governance misalignment: conditions that must be met simultaneously but advance at different speeds, with unequal legal force, with ambiguous signals, and across fleet segments that do not coincide. The obstacle is not the absence of regulation but its lack of synchronization, a diagnosis replicable for any fuel whose deployment depends on several regulatory domains. Full article

Hydrogen embrittlement (HE) remains one of the key challenges limiting the safe and reliable deployment of steels in hydrogen production, storage, transportation, and utilization systems. Artificial intelligence (AI) and machine learning (ML) have emerged as powerful tools for predicting HE behavior, accelerating materials development and selection, while supporting engineering decision-making. This paper systematically reviews and critically evaluates AI/ML applications for HE in steels through a structured analysis of all studies published between 2010 and 2026. The review examines experimental, literature-derived, and computational datasets together with data preprocessing, feature engineering, AI/ML models, validation strategies, and prediction objectives. Experimental datasets remain the dominant source for predicting HE susceptibility, hydrogen concentration, fracture behavior, and hydrogen-assisted cracking, whereas computational datasets provide complementary mechanistic insights into hydrogen diffusion, trapping, crack propagation, and atomistic interactions across multiple scales. Image- and signal-based modalities within these datasets further enable computer vision and automated defect characterization. Beyond systematically synthesizing the current literature, this review provides a critical and analytical evaluation of AI/ML datasets, model families, and prediction applications. It also establishes a practical framework for selecting appropriate AI/ML approaches according to dataset characteristics and engineering objectives. Future research should focus on standardized HE databases, rigorous external validation, explainable and uncertainty-aware AI, and closer integration of data-driven and physics-based approaches to improve predictive reliability, mechanistic understanding, and the safe deployment of hydrogen-compatible steels. Full article

Green hydrogen strategies proliferate across developing economies, yet most assume the planning authority possesses the state capacity, regulatory autonomy, and investment conditions that conflict-affected and fragile economies lack. Whether a strategy logic derived in one such context transfers to others with different institutional capacity remains untested. This study develops a Conflict-Affected Energy Transitions (CAET) framework and empirically examines its barrier gradient and conditional transferability propositions, analyzing at the country level a regional expert survey—data that prior single-case work, including the authors’ own, used only for binary external validation. A total of 137 energy experts across seventeen Arab states are grouped into three institutional clusters—conflict-affected/fragile, stable developing, and Gulf/high-capacity—and examined through cluster barrier and readiness profiles, a perceived-versus-predictive importance comparison, hierarchical clustering, and a Mode-A partial-least-squares path model with measurement invariance (MICOM) testing and permutation-based multi-group analysis. Energy justice and sovereignty are used as analytical and interpretive lenses, not as measured latent constructs in the structural model. Results show that barrier burdens follow a monotonic institutional fragility gradient: regulatory/institutional barriers rise from 3.02 (Gulf) through 3.52 (stable) to 4.06 (fragile), where they are the most severe constraint. Moreover, the perceived–predictive divergence—social barriers are rated least severe yet associate most strongly with sustainability—recurs across the region. In addition, the model satisfies compositional invariance across fragile and stable clusters while equality of regulatory means and variances fails as expected, and no structural path differs detectably between them at the current sample size. The adoption–governance–sustainability mechanism is therefore provisionally comparable rather than definitively invariant. We propose conditional transferability: the mechanism travels, provisionally, while priorities must be re-weighted by institutional context. Policy implications are differentiated—institutions-first, community-scale pathways for fragile states; finance and market formation for stable developing states; export-scale deployment for high-capacity states—and the CAET framework offers a generalizable alternative to techno-economic determinism for hydrogen strategy under constrained sovereignty. In practical terms, energy ministries in fragile states should sequence rule-making, permitting authority, and community-scale pilots before committing deployment capital; stable developing states should concentrate on de-risking finance and forming early offtake markets; and high-capacity states can proceed directly to export-scale projects and regional standard setting. Full article

In recent years, hydrogen-fueled internal combustion engines offer significant potential for achieving high efficiency and near-zero carbon emissions. However, stable combustion remains challenging due to the limited time available for fuel–air mixing, particularly in direct-injection concepts. This study investigates the influence of injector orientation on in-cylinder charge preparation in a heavy-duty spark-ignition engine operating with a side-mounted hydrogen direct-injection strategy. Three-dimensional computational fluid dynamics (CFD) simulations are performed to evaluate the effects of injector blow-cap inclination and azimuthal alignment on hydrogen jet evolution, flow-field development, and mixture formation. Under high-pressure injection conditions, hydrogen enters the cylinder as a highly under-expanded jet with strong momentum, resulting in significant interaction with the in-cylinder flow field. The results show that injector inclination influences jet impingement behavior, wall-guided flow development, and subsequent vortex evolution, while injector rotation modifies the interaction between the jet trajectory and in-cylinder swirl motion, affecting aerodynamic shear and flow-field complexity. The resulting mixture formation is evaluated through local air–fuel ratio distribution together with flow-field analysis and streamline evolution, demonstrating strong sensitivity to injector orientation and its coupling with in-cylinder aerodynamic structures. Quantitatively, injector orientation produces significant changes in the local air–fuel ratio distribution, with up to 25% reduction in the standard deviation of local air–fuel ratio for inclination variations and up to 35% for azimuthal variations between the extreme configurations, indicating improved mixture uniformity. Configurations promoting earlier jet disruption and enhanced spatial dispersion achieve more homogeneous charge preparation, whereas stronger wall-guided jet attachment results in localized fuel-rich regions. The findings provide physical insight into the role of jet–wall interaction, aerodynamic shear, and vortex restructuring in governing hydrogen mixing processes. The simulation framework captures the relevant in-cylinder flow physics and provides trends consistent with available experimental observations in the literature, which report improved efficiency and reduced NOx emissions under enhanced mixture homogeneity conditions. Full article

Morocco’s National Green Hydrogen Roadmap targets large-scale hydrogen exports, yet the offshore wind and tidal resources of the Atlantic Sahara coast remain underexplored, and single-resource electrolysis plants suffer from low, variable electrolyser utilisation. This study presents a reproducible, model-based techno-economic assessment of a 560 MW hybrid offshore wind–tidal hub at Dakhla that produces hydrogen by proton exchange membrane (PEM) electrolysis and exports it as liquid hydrogen (LH₂) to Jorf Lasfar. The assessment is entirely theoretical: it couples reanalysis-based resource characterisation, harmonic tidal modelling, hourly dispatch, and discounted levelised cost of hydrogen (LCOH) analysis, and does not include experimental or in situ measurements. The hybrid plant reaches a 45.5% capacity factor and produces 36,781 t of hydrogen per year at 60% electrolyser utilisation. The 2025 base-case production LCOH is 7.53 USD/kg (10.04 USD/kg delivered), falling to 4.45 USD/kg under a 2030 learning scenario that approaches the national 2–4 USD/kg target band. Because the wind and tidal resources are almost uncorrelated, hybridisation firms the supply and reduces electrolyser cycling rather than adding bulk energy; capacity factor and electrolyser-specific energy consumption are the dominant cost drivers. This work provides the first integrated wind–tidal hydrogen assessment for the Moroccan Atlantic coast and a transparent platform for future optimisation. Full article

Commercial aviation contributes approximately 3% of global CO₂ emissions, while nitrogen oxides (NO_x) remain a major environmental concern. Hydrogen is a promising carbon-free fuel for future gas turbine engines and offers a potential pathway towards net-zero aviation. This study presents the aerothermal design and CFD-based iterative refinement of an annular combustor for a hydrogen-fuelled CFM56-class large-bypass turbofan. The combustor was initially sized using established design correlations, with GasTurb14 providing the engine-cycle boundary conditions. CFD simulations were performed to evaluate the airflow distribution, temperature field, pressure loss and NO_x formation, and to optimize the cooling-hole arrangement. The final combustor achieved the target exit temperature of 1500 K with a pressure loss of 5.9%, meeting the design objective of approximately 6%. Relative to the initial hydrogen-fuelled configuration, the redesigned cooling-hole layout reduced the fuel-to-air ratio required to achieve the target exit temperature from 0.009 to 0.0073 (18.9%) and reduced the exit NO mass fraction from 0.003443 to 0.002223. A separate Large Eddy Simulation (LES) of the final combustor geometry was conducted to compare the combustion characteristics of hydrogen and Jet-A under identical operating conditions. The results demonstrate that cooling-hole configuration has a significant influence on combustor thermal performance and NO_x emissions, providing design guidance for future hydrogen-fuelled gas turbine combustors. Owing to the absence of experimental data for this configuration, the results are presented as a computational design study supported by a benchmark comparison rather than as an experimental validation. Full article

Liquid-hydrogen fuel-cell propulsion is a promising option for reducing the climate impact of short-range aviation, but its aircraft-level feasibility depends on the concurrent integration of cryogenic storage, megawatt-class propulsion systems, and thermal management. This paper presents an integrated conceptual design and technology-sensitivity assessment of a 101-passenger liquid-hydrogen fuel-cell aircraft, targeting a 1000 nmi design range and a 2040 entry into service, framed within the European Union FAME project. A JPAD-based aircraft sizing framework is coupled with a surrogate model for cryogenic tank sizing to investigate how selected hydrogen-subsystem characteristics propagate, through mission-fuel and tank-sizing convergence loops, to configuration-level performance and compliance with top-level aircraft requirements. The storage-system trade study identifies 2.0 bar as the most favourable sampled tank venting pressure; relative to the other investigated pressure levels, this solution reduces MTOM and design-mission block fuel by up to 8.1% and 9.2%, respectively. The propulsion-architecture study selects a four-engine layout as the best compromise between one-engine-inoperative performance, spanwise structural relief, nacelle drag, and mission fuel consumption, yielding a 2.6–2.7% lower MTOM and a 3.5–3.7% lower design-mission block fuel than the two- and six-engine alternatives. A technology-sensitivity matrix spanning 51–55% fuel-cell efficiency and 60–100% cooling-line speed recovery reveals a non-linear increase in installed power, aircraft mass, and hydrogen consumption as either parameter deteriorates. For the fixed-geometry FAME baseline, the onset of multiple TLAR violations occurs as speed recovery falls through approximately the 70–80% region, depending on fuel-cell efficiency. Within the assumptions of the present model, maintaining fuel-cell efficiency at or above approximately 53% and cooling-line speed recovery above this transition region therefore represents an approximate feasibility condition. Full article

The performance of a Proton Exchange Membrane Fuel Cell (PEMFC) stack is largely determined during assembly, where component materials, sealant selection, and clamping force jointly influence both sealing effectiveness and interfacial losses. These factors interact through coupled mechanical, thermal, and electrical phenomena. Although detailed multiphysics models can accurately capture these effects, their high computational cost limits their application in parametric analyses and optimisation studies. The Equivalent Stiffness Model (ESM) provides an efficient alternative, representing each stack component as a simplified stiffness formulation. Starting from an earlier ESM that reproduces the nonlinear compression of the Membrane Electrode Assembly (MEA) and sealants, this work adds the calculation of the electrical contact resistance at the Gas Diffusion Layer (GDL)–Bipolar Plate (BPP) interface and the resulting GDL porosity. Given the large number of input parameters, a Design of Experiments (DoE) approach systematically explores a wide range of stack configurations and operating conditions. The analysis shows that GDL type, sealant properties, and clamping force are the main drivers of assembly-related performance, whereas BPP material and thermo-hygrometric conditions become more influential during operation. These results provide quantitative guidance on which design and operating choices most strongly affect stack behaviour and under which conditions. Full article

Hydrogen (H₂) is widely regarded as a critical energy vector for achieving carbon neutrality, owing to its high energy density and CO₂-free combustion. Among sustainable production methods, photobiological H₂ synthesis using photosynthetic microorganisms has emerged as a promising strategy due to its ability to directly convert light energy into chemical energy. These biological systems use enzymatic pathways such as hydrogenases and nitrogenases to produce H₂ from water or organic substrates under moderate conditions. However, practical implementation remains limited by low solar-to-H₂ conversion efficiencies, oxygen sensitivity of catalytic enzymes, and technical challenges in photobioreactor systems. This paper reviews the current state of photobiological H₂ production, focusing on mechanistic challenges, photobioreactor design, substrate utilisation, and immobilisation techniques. Integrating biological and engineering approaches is expected to play a crucial role in advancing photobiological H₂ production towards large-scale implementation. Full article

Hydrogen sulfide (H₂S), a high-volume by-product of the hydrodesulfurization of fossil fuels, can be valorized by thermolysis to recover both molecular hydrogen and elemental sulfur, rather than being oxidized as in the conventional Claus process. The viability of this route depends on quantitative knowledge of the reaction mechanism and of the energy costs of dissociation, which are difficult to obtain experimentally at the temperatures involved. Here we study H₂S thermolysis by reactive molecular dynamics (RMD) with the ReaxFF potential for systems of 1000 H₂S molecules at 1 atm, addressing three coupled questions: the simulation parameters required for dilute gases, the energetics of dissociation, and the elementary reaction mechanism. The interaction cutoff radius proved critical: the original 10 Å value, parametrized for condensed systems, misses about 23 eV of attractive non-bonded interaction energy in the gaseous system at 298.15 K (≈0.023 eV per molecule) and fails to capture dissociation at 3000 K within 20 ns, whereas radii of 30–40 Å converge. Using a 40 Å cutoff at 2500, 3000 and 3500 K, atom-resolved species-transition records reveal a free-radical chain mechanism built from the same set of elementary steps at the three temperatures, whose relative contributions shift with temperature: S–H homolysis initiates the chain, hydrogen abstraction (H• + H₂S → H₂ + HS•) is essentially the exclusive source of H₂ (persistent H• + H• recombination contributed only 1, 13 and 17 events, below 0.5% of the abstraction count), and a slow sulfur-condensation stage (S₂ → S₃ → S₄) limits the net conversion, which reached 9.3 ± 0.9%, 26.3 ± 1.4% and 46.7 ± 1.6% within the simulated windows (single-trajectory counting resolution)—kinetically limited values, not equilibrium conversions. The enthalpy of the system rises linearly with the number of H₂S molecules consumed (R² ≥ 0.99), defining energy costs of 2.46 ± 0.04, 3.10 ± 0.08 and 3.95 ± 0.18 eV per molecule that increase with temperature by ≈1.48 eV per 1000 K; at 3500 K the cost lies between the 0 K complete-dissociation limit D₀ = 3.90 eV derived from the experimental H–SH bond energy and the Kirchhoff-corrected complete-dissociation enthalpy at that temperature (4.11–4.12 eV), statistically indistinguishable from the latter (a 0.9σ difference). These results provide a thermochemically validated, molecular-level basis for engineering the valorization of residual H₂S as a source of green hydrogen. Full article

Underground storage of green hydrogen is a strategic enabler of large-scale renewable deployment, but its feasibility rests on a hard problem: keeping a small, highly mobile molecule confined underground for decades without safety or environmental risk. This critical review examines the containment mechanisms of hydrogen across underground storage types, focusing on geological barriers, well integrity and sealing materials. We evaluate the containment capabilities of salt cavities, deep aquifers and depleted reservoirs, with particular attention to the viscoplastic, self-healing properties of salt that promote confinement, and to the vulnerabilities of well infrastructure and salt–cement interfaces. Emerging alternatives, including lined rock caverns and repurposed abandoned mines, are assessed alongside their distinct operating configurations and use cases. Leakage mechanisms including diffusion, advection, microcracking, cement degradation and hydrogen–material interactions are analysed alongside geomechanical modelling, microbial activity, monitoring strategies, regulatory frameworks, and techno-economic and environmental considerations, including the integration of carbon capture, utilisation and storage (CCUS) with underground hydrogen storage. Well integrity emerges as the dominant risk factor across storage types. The review concludes with design criteria, monitoring priorities and research needs to guide the safe, sustainable deployment of underground hydrogen storage, providing a scientific foundation for future numerical and experimental work on storage tightness. Full article

Liquid hydrogen (LH₂) has been regarded as an ideal carrier for large-scale and long-distance hydrogen energy storage and transportation due to its high gravimetric hydrogen storage density, rapid refueling efficiency and favorable safety performance. However, the physical properties of LH₂, such as low viscosity and high volatility at the ultra-low temperature of −253 °C, cause complex thermodynamic problems during the refueling process—including drastic phase transitions, concentrated thermal stress, and two-phase flow instability—which act as bottlenecks restricting the large-scale application of LH₂. In this paper, research advances achieved domestically and internationally in recent years are reviewed in detail with respect to thermodynamic issues occurring in the ultra-low-temperature LH₂ refueling process. Research achievements concerning the thermodynamics of LH₂ refueling are classified, summarized and discussed from the perspectives of theoretical thermodynamic analysis, numerical simulation, experimental investigation and refueling process optimization strategies for LH₂ refueling. The heat and mass transfer mechanisms involved in LH₂ refueling are revealed, the variation in thermodynamic responses during the refueling process is described, the critical factors affecting the thermodynamic behaviors of LH₂ refueling are clarified, the industry standards on LH₂ refueling are critically assessed, and various refueling process management strategies are discussed. Finally, the future development directions of thermodynamic research on the LH₂ refueling process are discussed and prospected on the basis of the development trends and potential prominent challenges faced by LH₂ refueling technologies. Full article

The electrochemical regeneration of sodium borohydride (NaBH₄) from spent metaborate is a central bottleneck for circular hydrogen storage. (1) Background: The eight-electron reduction of the aqueous borate species B(OH)₄⁻ to BH₄⁻ is thermodynamically out-competed by the hydrogen-evolution reaction (HER) by about 0.41 V at every pH, so selectivity can only be won kinetically. (2) Methods: We advance an ambiphilic-site hypothesis, screen 30 candidate metal centres using entirely experimental, tabulated descriptors (bulk HER exchange current density; gas-phase M-O bond energy) with no new electronic-structure computation, and then audit the transferability of both descriptor axes against published, corrected DFT datasets for nitrogen-coordinated single-atom sites. (3) Results: At the parent-metal level, the two axes are orthogonal (Spearman ρ = 0.02) and the score passes a family-level experimental validation over seven bulk-electrode metals (ρ = 0.69; exact permutation p = 0.050), separating the HER-dominated noble-metal family from the single-atom Mn benchmark. The site-level audit shows that the oxophilicity axis transfers to M-N₄ sites almost quantitatively (ρ = −0.84 pyridine-4N, −0.95 pyrrole-4N, n = 23) while the bulk HER axis does not, and that site-level scaling between oxygen and hydrogen binding narrows the productive window to oxophilic centres that over-bind hydrogen. (4) Conclusions: The site-anchored screen redirects the search from the parent-metal leaders (La, Ce, Y, Ti, Sc) to refractory single-atom centres, with W, Nb and Mo as priority synthesis targets (Re excluded on scarcity; Zr, Hf, Ta as data-supported extensions; Ti as the sustainability-anchored borderline case) and the lanthanides retained only as explicitly extrapolative candidates. All data and analysis code are openly deposited. Full article

The transportation sector is a major contributor to global greenhouse gas emissions, driving the need for low-carbon energy solutions. Hydrogen is increasingly recognised as a promising option for decarbonising heavy-duty and long-distance transport; however, hydrogen storage systems contribute significant environmental burdens through material production, manufacturing and end-of-life challenges. This study presents a comparative life cycle assessment of a conventional Type IV composite pressure vessel and a novel additively manufactured, internally reinforced titanium alloy pressure vessel concept for heavy-duty vehicle applications. The two pressure vessel designs were compared within the same available packaging volume on a heavy-duty vehicle. A cradle-to-grave system boundary was applied, covering production, manufacturing, transport, use and end-of-life stages. The environmental assessment was limited to cumulative energy demand and CO₂ emissions, which were used as the metrics for comparing the two hydrogen storage systems. Across the entire life cycle, the Type IV pressure vessel exhibited approximately 16% lower energy demand and CO₂ emissions that the titanium alloy pressure vessel. The use phase dominated both energy demand and environmental impacts, contributing more than 75% of the total life cycle impacts for both pressure vessel designs due to the high energy demand for hydrogen production. For the manufacturing phase, when normalised per kilogram of pressure vessel, the Type IV vessel produced 21.9 kgCO₂eq/kg, compared with 80 kgCO₂eq/kg for the titanium alloy vessel. Material production dominated the cradle-to-gate impact of the titanium alloy pressure vessel, primarily because of the energy-intensive primary production of titanium. Although the use of recycled titanium was also assessed, it reduced the manufacturing stage impacts by only 9%, and the overall impacts remained higher than those of the composite alternative. Full article

The hydrogen economy has emerged as a promising pathway to address climate change and ensure long-term global energy security, with water electrolysis powered by renewable energy as a key enabler of sustainable hydrogen production. Recent advances in various electrolyser technologies have enhanced their suitability for industrial applications, creating new opportunities for deploying green hydrogen. To address the gap in integrated, multi-dimensional assessment tools for groundwater-based hydrogen systems in water-scarce developing countries, this study develops and presents a Structured Assessment Framework for Green Hydrogen Production from Groundwater in South Africa—the first framework to simultaneously integrate hydrogeological sustainability screening, electrolyser technology selection under groundwater quality constraints, disaggregated levelised cost of hydrogen (LCOH) analysis including water treatment costs, comparative life cycle assessment (LCA) of green, blue, and grey hydrogen pathways, and policy and governance alignment within a single operationalised architecture. This included integrating five thematic dimensions: groundwater resource assessment, electrolyser technology integration, economic viability, environmental sustainability, and policy and governance considerations. This systematic review was conducted in accordance with the PRISMA 2020 guidelines, drawing on 130 studies retrieved from Scopus and Web of Science (2015–2025). The analysis examines groundwater quality and suitability, the technical feasibility of electrolyser systems, and the comparative implications of grey, blue, and green hydrogen pathways on cost and environmental performance. The framework also provides strategic guidance for deploying renewable-energy-powered hydrogen systems, emphasising life-cycle impacts, regulatory alignment, and the potential for decentralised hydrogen hubs. Findings highlight the significance of strengths, weaknesses, opportunities, and threats (SWOT) for green hydrogen production using groundwater in South Africa, including export potential and strong linkages to the circular economy. The study offers actionable insights for policymakers, planners, and industry stakeholders seeking to advance a sustainable and economically competitive hydrogen landscape. Full article

Electrified steam methane reforming (eSMR) is emerging as a promising technology for the decarbonization of the chemical industry and low-carbon hydrogen production by coupling renewable electricity with renewable gaseous feedstocks such as biomethane. In this work, structured Ni-based catalysts washcoated on highly thermally conductive SiC open-cell foams (OCFs) were developed and evaluated for biomethane steam-reforming operating conditions. Two catalyst formulations, 30 wt.% Al₂O₃_30 wt.% CeO₂_20 wt.%Ni and SiC_30 wt.% Al₂O₃_30 wt.%Ce_0.25Zr0.75 O₂_20 wt.%Ni, were tested in a laboratory-scale indirectly electrically heated reformer. The high thermal conductivity of the SiC-structured support ensured efficient heat transfer throughout the reactor, limiting radial temperature gradients to below 10 °C. Both catalyst formulations exhibited excellent catalytic performance; however, the Ce_0.25Zr0.75O₂-promoted catalyst achieved the best results, maintaining equilibrium methane conversion at a gas hourly space velocity above 7000 h⁻¹ while reaching a specific electrical energy consumption of 2.06 kWh/Nm³ of produced H₂ projected for industrial-scale efficiency. Notably, these performances were obtained with a catalyst loading approximately 20–50% lower than that of conventional commercial alumina pellet catalysts. XRD characterization did not reveal the formation of crystalline graphitic carbon after catalytic operation. Furthermore, the structural evolution of the Ce–Zr–O highlights the active role of the mixed oxide in promoting redox processes and maintaining catalytic activity under reaction conditions. Overall, these results demonstrate that the combination of highly conductive SiC-structured supports and Ce–Zr-promoted Ni catalysts significantly enhances both the thermal and catalytic efficiency of eSMR. The proposed catalyst provides a promising route toward compact, energy-efficient, and decentralized hydrogen production from biomethane, supporting the electrification and decarbonization of future hydrogen generation technologies. Full article

Hydrogen has emerged as a promising energy carrier for sustainable, low-carbon energy systems because of its high energy density and compatibility with fuel cell technologies. This study presents a comprehensive investigation of hydrogen production through the integration of steam methane reforming (SMR), solar photovoltaic (PV) power generation, proton exchange membrane (PEM) electrolysis, hydrogen storage, and PEM fuel cells. A three-dimensional computational fluid dynamics (CFD) model was developed to analyze fluid flow, heat transfer, species transport, and chemical reactions within a catalytic steam methane reformer. The simulation predicted a methane conversion of 94.71%, a hydrogen yield of 3.75 mol H₂/mol CH₄, and an overall efficiency of 63.35%, indicating highly efficient hydrogen production. Sensitivity analyses identify catalyst temperature, inlet temperature, and residence time as the dominant parameters affecting hydrogen yield. Integration with renewable energy systems demonstrated that a hybrid configuration consisting of a 120 kW PV array, a 50 kW PEM electrolyzer, a 6 kW PEM fuel cell, and 6–8 kg hydrogen storage can effectively support sustainable hydrogen production and auxiliary power demands. The proposed framework provides a practical pathway for integrating thermochemical and renewable hydrogen technologies into future energy applications worldwide. Full article

The transition towards climate-neutral metallurgical production requires a broader transformation than the simple substitution of fossil-fuel combustion with electrical heating. While process electrification is a fundamental step towards reducing greenhouse gas emissions, achieving truly sustainable high-temperature processing also depends on the ability to maintain tightly controlled reaction environments, minimise thermal losses, and maximise the efficient use of process gases. These factors become increasingly important as the industry moves towards hydrogen-assisted processing routes and greater integration of renewable energy sources. By controlling heat transfer and gas composition, a stable processing environment can be maintained in which temperature, and gases’ partial pressure, can be accurately regulated throughout the treatment cycle. This study introduces the engineering concept of an airtight electrified indirect-fired rotary furnace, developed as a new process for efficient calcination, and also, hydrogen-based reduction processes. To assess the applicability of the proposed reactor concept, a bench-scale experimental campaign was carried out using two representative metallurgical processes: magnesite calcination and hydrogen-assisted reduction of lateritic ores. Throughout the testing campaign, the reactor maintained stable thermal conditions and a well-controlled process atmosphere, while the integrated monitoring system enabled continuous observation of temperature evolution and gas composition. The calcination trials achieved conversion efficiencies above 98%, whereas the hydrogen-reduction experiments successfully promoted the transformation of iron and nickel oxide phases into their metallic state. The results demonstrate that the integration of indirect electrical heating with airtight reactor operation provides a robust platform for hydrogen-assisted thermal processing. The proposed architecture improves atmosphere control and process efficiency while offering a scalable solution for the future implementation of electrified, low-carbon metallurgical technologies. Full article

This study presents a mathematical programming approach for the optimal design of a renewable energy system in a grid-connected public building, incorporating green hydrogen production for surplus energy storage. The system includes wind turbines, solar panels, batteries, a hydrogen unit, and a grid connection. Hydrogen can also be sold as vehicle fuel, generating revenue and reducing the environmental impact. Unlike traditional hydrogen smart grid models that rely on continuous capacity variables—which often yield non-commercial fractional unit sizes—our MILP framework strictly enforces discrete equipment capacities matching real-world procurement specifications. The methodology is applied to the Chemical Engineering Department Building at the University of Patras, Greece, with two objectives: minimizing annual cost and minimizing carbon dioxide emissions. While higher grid electricity tariffs increase absolute total energy costs, they significantly enhance the economic competitiveness and payback of local renewable energy and green hydrogen installations, shifting the optimal system configuration toward self-sufficiency and deep decarbonization. Emission minimization achieves substantial reductions with acceptable economic trade-offs, mainly through hydrogen replacing fossil fuels in transport. A GAMS-based model demonstrates that integrating renewables and hydrogen storage can enhance energy security, lower costs, and reduce the environmental impact in public buildings. Full article

Hydrogen blending into natural gas grids can support early renewable hydrogen deployment, but admissible injection depends on local gas flow, blending limits, and upstream hydrogen concentrations. This paper analyses these effects for a regional high-pressure gas-grid section in Styria, Austria, with two hydrogen injection points. A transient gas-network model derives time- and location-dependent injection limits, which are integrated into an electrolyser dispatch optimisation with fixed trailer demand and annual gas-grid injection demand. Three cases are compared: unrestricted injection, a “CH₄-based” limit without upstream hydrogen, and an “H₂-aware” case representing potential upstream hydrogen injection. For the analysed configuration, blending constraints shift operation away from favourable electricity-price periods, particularly when low prices coincide with reduced gas demand. In the 2025 reference case, the “H₂-aware” constraint increases the electricity-cost contribution from 4.22 to 5.45 EUR/kg_H2. A robustness analysis using electricity-price series for 2020, 2022, and 2025 shows that the “H₂-aware” constraint increases the electricity-cost contribution by 15.8–29.1% relative to unrestricted injection. The results demonstrate that dynamic gas-grid constraints should be considered when assessing blending-based electrolyser projects, while the quantitative findings remain specific to the analysed network and assumptions. Full article

Methane cracking has emerged as a promising route for sustainable hydrogen production because it avoids direct carbon dioxide emissions while simultaneously enabling carbon sequestration in the form of solid carbon. In this work, a comprehensive and systematic experimental investigation of catalytic methane cracking was performed by directly comparing a commercial nickel catalyst (KATALCO™ 25-4MQ), an in-house catalyst prepared by wet impregnation using Fe(NO₃)₃·9H₂O as the iron precursor and Puralox SCFa-160 Ce20 as the support, and non-catalytic thermal conditions under identical operating parameters. Experiments were carried out in a laboratory-scale fixed-bed reactor at atmospheric pressure by varying methane partial pressure (0.1–0.2 atm) and operating temperature (600–800 °C), while maintaining a constant methane-specific WHSV of 0.3 h⁻¹. Continuous online gas analysis was employed to monitor reactor performance, and a dedicated post-processing methodology, including nitrogen-tracer-based carbon balance calculations, was developed to validate the experimental results. The results demonstrated the strong beneficial effects of both temperature and catalytic materials on methane decomposition. The Fe-based catalysts exhibited the highest performance, achieving average methane conversions and hydrogen yields approaching 50%, with peak values exceeding 90% under the most favorable conditions. Commercial Ni catalysts also showed promising activity, although a more pronounced deactivation tendency was observed during prolonged operation. Conversely, non-catalytic tests resulted in substantially lower performance. Overall, this work provides an experimentally assessed and integrated methodology together with benchmark performance indicators that may serve as useful guidance for researchers, process designers, and practitioners involved in the development, optimization, and future scale-up of methane cracking technologies for turquoise hydrogen production. Full article

The cement industry is one of the most challenging sectors to decarbonize due to the coexistence of high-temperature thermal demand and process-related emissions from limestone calcination. This study presents an energy and emissions assessment of cement manufacturing based on representative mass and energy balances derived from literature benchmarks and industrial operating data. Typical cement production requires 2.8–3.6 GJ of thermal energy and 80–120 kWh of electricity per tonne of final product, resulting in total emission in the range 500–850 kg CO₂/t cement, of which 55–65% originate from clinker calcination. Moving from this baseline, possible decarbonization pathways are evaluated, including energy efficiency improvements, clinker substitution through supplementary cementitious materials use of alternative fuels, electrification, hydrogen utilization and carbon capture technologies. The analysis shows that energy efficiency measures provide relatively limited reductions (10–30 kg CO₂/t cement), while alternative fuels and clinker substitution can achieve larger but still partial benefits. Hydrogen emerges as a promising option for decarbonizing the combustion-related share of emissions, with a potential reduction ranging from 50 to 200 kg CO₂/t cement, particularly when integrated with oxy-fuel combustion systems. Deep decarbonization ultimately requires carbon capture and storage (CCS), the only technology capable of addressing the substantial process emissions inherent to clinker production and use of hydrogen can be relevant too. Full article

Handling hydrogen-rich atmospheres requires materials that do not deteriorate in the presence of hydrogen and that ensure safe operation. Often high strength metallic materials, however, may show catastrophic mechanical failure in the presence of hydrogen. This phenomenon, called hydrogen embrittlement, can be very dangerous, as these failures occur in a time-delayed and sudden manner. Two commercially available materials, AMPCOLOY^® 83, a copper beryllium alloy, and AMPCO^® 18, an aluminum bronze, have been investigated to clarify their susceptibility to hydrogen embrittlement. Hydrogen permeation measurements were performed to assess diffusivity in the materials, and hydrogen content was analyzed by thermal desorption analysis (TDA) after electrochemical charging. Mechanical properties in hydrogen-affected state were assessed by slow strain rate tensile tests (SSRT), with in situ electrochemical charging and post-test fractographic inspection of the fracture surfaces. While the aluminum bronze showed no noticeable hydrogen-related deterioration, copper beryllium alloy experienced some embrittlement, however, having a low fracture strain even in the uncharged state. Full article

Dynamic membrane bioreactors (DMBRs) are promising systems for continuous biohydrogen production because they enable effective biomass retention under short hydraulic retention time (HRT) conditions. In this study, a dynamic membrane bioreactor coupled with electro-fermentation (DMBR-EF) was operated for 59 days to investigate the effect of applied voltage on biohydrogen production and metabolic flux regulation. The reactor was sequentially operated at 0 (no applied voltage), 0.2, 0.4, 0.6, 0.8, and 1.0 V using glucose as a model substrate. The highest hydrogen production rate (HPR) and hydrogen yield (HY) were achieved at 0.2 V, reaching 15.35 ± 0.48 L H₂/L/d and 1.54 ± 0.05 mol H₂/mol glucose_added, respectively, which were 33.71% and 33.91% higher than those of the 0 V control. At 0.2 V, residual glucose and effluent volatile suspended solids (VSS) were minimized, while butyric acid (HBu) formation was enhanced and lactic acid (HLa) accumulation was suppressed. In contrast, voltages above 0.4 V reduced hydrogen recovery by shifting metabolic flux toward HLa, propionic acid (HPr), formic acid (HFo), and homoacetogenic pathways. Microbial analysis showed that Clostridium dominated under all conditions, but voltage application selectively altered the relative abundance and metabolic output of Clostridium-related amplicon sequence variants (ASVs). These results indicate that mild electrochemical stimulation at 0.2 V effectively enhances continuous biohydrogen production by promoting butyric acid-type fermentation, suppressing lactic acid accumulation, and reducing hydrogen loss through competing metabolic pathways in DMBR-EF systems. Full article

The accelerating energy transition and growing geopolitical uncertainty have strengthened the strategic importance of hydrogen within future low-carbon energy systems. Green hydrogen is increasingly recognized as a key energy carrier supporting industrial decarbonization, renewable energy integration, long-term energy storage and energy security. However, existing hydrogen market assessment approaches remain fragmented and frequently focus on isolated technological, regulatory, or investment-related dimensions without sufficiently integrating the systemic interactions that shape hydrogen market maturity. To address this research gap, this study proposes the Integrated Green Hydrogen Market Development Index (IGHMDI), a multidimensional composite indicator framework designed to evaluate hydrogen market development through the integration of regulatory, technological, infrastructural, financial and strategic dimensions. This methodological framework is based on established principles of composite indicator construction, including indicator selection, normalization, weighting, and aggregation procedures adapted to the characteristics of emerging hydrogen markets. The proposed framework incorporates six principal dimensions: regulatory and policy development, technological readiness, infrastructure and market integration, investment and financial readiness, market demand and industrial adoption, and international cooperation and strategic positioning. An illustrative pilot application comparing Croatia and Germany is used to demonstrate the operational logic of the framework and its ability to distinguish between hydrogen markets at different stages of development. The illustrative assessment produced composite IGHMDI scores of 65.0 for Croatia and 91.7 for Germany, demonstrating the framework’s capability to distinguish hydrogen markets at different stages of structural development while providing a transparent basis for comparative assessment. The results indicate that hydrogen market development increasingly depends on the interaction between regulatory stability, infrastructure readiness, technological innovation, investment support mechanisms, market demand, and international coordination. The study also acknowledges that broader empirical validation, sensitivity analysis, and longitudinal application across a larger set of countries are required in future research. Overall, the IGHMDI framework contributes to the development of multidimensional hydrogen market assessment methodologies and provides a transparent analytical tool for comparative benchmarking, policy evaluation, infrastructure prioritization, and future hydrogen transition governance. Full article