Japan

Hydrogen is considered a clean and efficient energy carrier crucial for shapingthe net-zero future. Large-scale production transportation storage and use of greenhydrogen are expected to be undertaken in the coming decades. As the smallest element inthe universe however hydrogen can adsorb on diffuse into and interact with many metallicmaterials degrading their mechanical properties. This multifaceted phenomenon isgenerically categorized as hydrogen embrittlement (HE). HE is one of the most complexmaterial problems that arises as an outcome of the intricate interplay across specific spatialand temporal scales between the mechanical driving force and the material resistancefingerprinted by the microstructures and subsequently weakened by the presence of hydrogen. Based on recent developments in thefield as well as our collective understanding this Review is devoted to treating HE as a whole and providing a constructive andsystematic discussion on hydrogen entry diffusion trapping hydrogen−microstructure interaction mechanisms and consequencesof HE in steels nickel alloys and aluminum alloys used for energy transport and storage. HE in emerging material systems such ashigh entropy alloys and additively manufactured materials is also discussed. Priority has been particularly given to these lessunderstood aspects. Combining perspectives of materials chemistry materials science mechanics and artificial intelligence thisReview aspires to present a comprehensive and impartial viewpoint on the existing knowledge and conclude with our forecasts ofvarious paths forward meant to fuel the exploration of future research regarding hydrogen-induced material challenges.

As Europe transitions away from natural gas dependency and accelerates its adoption of renewable energy 12 green hydrogen has emerged as a key energy carrier for industrial and automotive applications. Similarly plans 13 to export hydrogen and ammonia from resource-rich regions like Australia and the Middle East to major importers 14 such as Japan and South Korea underline the global commitment to decarbonization. Central to these efforts is 15 the advancement of efficient hydrogen compression technologies which are essential for establishing a 16 sustainable hydrogen supply chain. This study provides a comparative analysis of two key hydrogen compression 17 technologies categorized under positive displacement and non-mechanical systems. The evaluation emphasizes 18 the technical characteristics energy efficiency and potential applications of these systems in the emerging 19 hydrogen economy. Special focus is placed on electric motor-driven compressors which integrate advanced 20 materials and optimized designs to enhance efficiency and minimize energy consumption. By addressing the gap 21 in comparative evaluations this paper offers insights into the performance and sustainability of these technologies 22 contributing to the development of cost-effective and reliable hydrogen supply systems.

Japan and other industrialized countries rely on the import of green hydrogen (H2 ) as they lack the resources to meet their own demand. In contrast countries such as Australia have the potential to produce hydrogen and its derivatives using wind and solar energy. Solar energy can be harnessed to produce electricity using photovoltaic systems or to generate thermal energy by concentrating solar irradiation. Thus thermal and electrical energy can be used in a solid oxide electrolysis process for low-cost hydrogen production. The operation of a solid oxide electrolysis cell (SOEC) stack integrated with solar energy is experimentally investigated and further analyzed using a validated simulation model. Furthermore a techno-economic assessment is conducted to estimate the hydrogen production costs including the expenses associated with liquefaction and transportation from Australia to Japan. High conversion efficiencies and low-cost SOECs are projected to result in production costs below 4 USD/kg.

Recent studies on additive manufacturing (AM) have indicated the necessity of understanding the hydrogen embrittlement (HE) of high-strength steels fabricated by AM due to the different microstructure obtained compared to their conventionally processed counterparts. This study investigated the influence of post-AM tempering (at 205 ◦C 315 ◦C and 425 ◦C) on the HE resistance of AM-fabricated AISI 4340 steel a representative ultrahigh-strength medium-carbon low-alloy steel. The present results show that tempering effectively reduced the HE sensitivity of the steel. When tested in air tempering at a low temperature of 205 ◦C slightly increased both the yield strength (YS) and ultimate tensile strength (UTS) accompanied by a reduction in elongation (EL). This behaviour is attributed to the precipitation of carbides. In contrast higher tempering temperatures of 315 ◦C and 425 ◦C resulted in a progressive decrease in both YS and UTS as anticipated. However when tested in a hydrogen-rich environment although the HE dramatically reduced the ductility and YS could not even be determined for the samples tempered at 205 ◦C and 315 ◦C the tempered samples retained higher UTS and EL compared to the as-AM-fabricated samples because of the increased HE resistance by tempering. Microstructural examination indicated that tempering at 205 ◦C and 315 ◦C retained the bainitic microstructure while promoting the formation of fine carbide precipitates which softened the bainitic ferrite matrix enhancing the hydrogen trapping capacity. Tempering at 425 ◦C promoted recovery of the AM-fabricated steel reducing dislocation density producing a lower subsurface hydrogen concentration and higher hydrogen diffusivity which led to an enhanced HE resistance. As a result testing of the samples tempered at 425 ◦C in hydrogen resulted in a high YS (~1200 MPa) and only a ~5 % reduction in UTS and a 64 % reduction in EL compared with the untempered samples of which the reductions were 31 % in UTS and 79 % in EL. Furthermore this study underscores the critical role of the trap character in governing the HE behaviour offering a pathway toward optimised heat treatment strategies for improved HE resistance of additively manufactured high-strength steels.

Hydrogen production is increasingly vital for global decarbonization but remains a waterand energy-intensive process especially in arid regions. Despite growing attention to its climate benefits limited research has addressed the environmental impacts of water sourcing. This study employs a life cycle assessment (LCA) approach to evaluate three water supply strategies for hydrogen production: (1) seawater desalination without brine treatment (BT) (2) desalination with partial BT and (3) freshwater purification. Scenarios are modeled for the United Arab Emirates (UAE) Australia and Spain representing diverse electricity mixes and water stress conditions. Both electrolysis and steam methane reforming (SMR) are evaluated as hydrogen production methods. Results show that desalination scenarios contribute substantially to human health and ecosystem impacts due to high energy use and brine discharge. Although partial BT aims to reduce direct marine discharge impacts its substantial energy demand can offset these benefits by increasing other environmental burdens such as marine eutrophication especially in regions reliant on carbon-intensive electricity grids. Freshwater scenarios offer lower environmental impact overall but raise water availability concerns. Across all regions feedwater for SMR shows nearly 50% lower impacts than for electrolysis. This study focuses solely on the environmental impacts associated with water sourcing and treatment for hydrogen production excluding the downstream impacts of the hydrogen generation process itself. This study highlights the trade-offs between water sourcing brine treatment and freshwater purification for hydrogen production offering insights for optimizing sustainable hydrogen systems in water-stressed regions.

In the present study pilot simulations of the phenomena of blast wave and fireball generated by the rupture of a high-pressure (35 MPa) hydrogen tank (volume 72 L) due to fire were carried out. The computational fluid dynamics (CFD) model includes the realizable k-ε model for turbulence and the eddy dissipation model coupled with the one-step chemical reaction mechanism for combustion. The simulation results were compared with experimental data on a stand-alone hydrogen tank rupture in a bonfire test. The simulations provided insights into the interaction between the blast wave propagation and combustion process. The simulated blast wave decay is approximately identical to the experimental data concerning pressure at various distances. Fireball is first ignited at the ground level which is considered to be due to stagnation flow conditions. Subsequently the flame propagates toward the interface between hydrogen and air.

To consider an appropriate evaluation method for hydrogen compatibility slow strain rate tensile (SSRT) tests were conducted on high strength piping materials cold-worked type 316 austenitic stainless steel (SUS316CW) and iron-based superalloy A286 used in hydrogen stations for two years.<br/>SUS316CW used at room temperature in 82 MPa gaseous hydrogen contained 7.8 mass ppm hydrogen. The SSRT test of SUS316CW was conducted in nitrogen at -40 °C. The fracture surface showed dimples and no hydrogen embrittlement behavior was observed. While the SSRT test of SUS316CW in 70 MPa gaseous hydrogen at -40 °C showed a slight decrease in reduction area and a brittle fracture morphology in the outer layer. This was considered to be the effect of high-pressure gaseous hydrogen during the SSRT test in addition to the pre-contained hydrogen.<br/>A286 used at -40 °C in 82 MPa gaseous hydrogen contained negligible hydrogen (0.14 mass ppm). SSRT tests were conducted at 150 °C in 70 MPa gaseous hydrogen and in air and showed a low relative reduction in area (RRA) value. To investigate the decrease in the RRA we switched the gas from hydrogen to air in the middle of the SSRT test and closely examined the RRA values and fracture morphology including side cracks. The hydrogen embrittlement was found to originate from the elastic deformation region. Stress cycling in the elastic deformation region also accelerated the effect of hydrogen. These were attributed to an increase in the lattice hydrogen content. While in the plastic deformation region hydrogen trapped in the defects and hydrogen through the generated surface cracks increased the hydrogen content at the crack tips reducing the RRA value. And there was a good correlation between the crack lengths and RRA values.<br/>Then hydrogen embrittlement mechanism depends on the operating conditions (stress and temperature) of the material and evaluating the hydrogen compatibility of materials by controlling their hydrogen content and strain according to the service environment is desirable.

One of the significant safety concerns in large-scale storage and transportation of liquefied (cryogenic) hydrogen (LH2) is the formation of flammable hydrogen/air mixtures after leakages during storage or transportation. Especially in maritime transportation hydrogen accumulations could occur within large and congested geometries. The installation of passive auto-catalytic recombiners (PARs) is a suitable mitigation measure for local areas where venting is insufficient or even impossible. Numerical models describing the operational behavior of PARs are required to allow for optimizing the location and assessing the efficiency of the mitigation measure. In the present study the operational behavior of a PAR with a compact design has been experimentally investigated. In order to obtain data for model validation an experimental program has been performed in the REKO-4 facility a 5.5 m³ vessel. The test procedure includes two phases steady-state and dynamic. The results provide insights into the hydrogen recombination rates and catalyst temperatures under different boundary conditions.

Hydrogen embrittlement (HE) poses a significant challenge for high-strength steels. Although HE of wrought steels has been extensively studied it remains limited in steels processed by additive manufacturing (AM). The present work (i) compares the HE susceptibility of AISI 4340 ultra-high-strength steel fabricated by selective laser melting (SLM) with its wrought counterpart; (ii) investigates the predominant factors and possible HE mechanisms in the AM-fabricated material; and (iii) correlates microstructures produced with different SLM processing parameters to HE susceptibility of the steel. Generally conventionally processed AISI 4340 steel is used with a tempered martensitic structure to ensure the ultrahigh strength and therefore is susceptible to HE. In contrast SLM-fabricated 4340 exhibits a uniform refined bainitic microstructure. How this change of microstructure influences the HE susceptibility of the steel is unknown and needs investigation. Our results demonstrate that at the same level of strength the SLM-fabricated 4340 steel exhibits significantly lower HE susceptibility than its wrought counterpart. The SLM-fabricated steel showed a higher hydrogen diffusion rate. Furthermore the refined microstructure of the SLM-fabricated steel contributes to enhanced ductility even with hydrogen. These findings indicate that AM of high-strength steels has strong potential to improve HE resistance providing a pathway to solve this long-term problem. This study highlights the critical role of microstructure in influencing HE and offers valuable insights for developing steels for hydrogen applications.

‘Green’ hydrogen produced by the electrolysis of water using renewable energy sources is expected to become a versatile energy carrier in the future. This study examined the techno-economic performance of combined offshore wind-solar energy systems for hydrogen production in Choshi Chiba Prefecture Japan a region with high average wind speeds. Hourly wind speed and solar radiation data were used to simulate hydrogen production under two system configurations: unlimited power cuts without batteries and no power cuts with battery storage. In the no-power-cut case battery integration increased the nominal hydrogen cost by 43.8 % 17.7 % and 19.8 % in 2025 2030 and 2050 respectively. However sensitivity analysis considering higher electrolyzer OPEX due to degradation revealed that the unlimited power-cut system can become more expensive making battery-supported systems economically favorable over the long term. These findings highlight the importance of integrating battery storage to enhance technical reliability and economical pathways for offshore wind–solar hydrogen production systems.