Hydrogen storage alloys are an extremely important material for achieving a hydrogen society in future, as they enable hydrogen to be used as a green energy carrier. These alloys possess the excellent property of being able to store and release large amounts of hydrogen near room temperature and atmospheric pressure. They are used in a variety of applications, such as in Nickel hydride batteries and Hydrogen storage alloy tanks. This paper provides an overview of the development of these hydrogen storage alloys, their properties and their practical applications, concluding with a discussion of future prospects.

To support Japan's 2050 carbon neutrality goal, Japan Steel Works M&E, Inc. (JSW M&E) has developed and commercialized advanced hydrogen storage solutions based on metal hydride (MH) tanks. These tanks utilize the reversible hydrogen absorption properties of LaNi₅- and FeTi-based alloys, achieving high hydrogen volumetric storage densities―500 to 600 times the tank volume. JSW’s proprietary Hydrage^TM technology, which blends MH powder with resin, effectively mitigates adverse effects caused by alloy expansion and powder pulverization, while also reducing combustibility. This reduced combustibility achieved results non-hazardous materials by Japan’s Fire Service Act. In addition, the tanks’ low internal gas pressure and solid-state hydrogen storage allow for flexible compliance with the High Pressure Gas Safety Act and the Building Standards Act. These regulatory advantages, combined with compactness and safety, have contributed to the growing adoption of MH tanks in diverse hydrogen storage applications.

This paper introduces the utilization of hydrogen absorbing alloy tanks (MH tanks) in the hydrogen storage and delivery system developed under the “Project to Construct and Demonstrate a Low-Pressure Hydrogen Delivery Model for Small-Scale Consumers Using an Existing Gas Delivery Network”, conducted as part of the Ministry of the Environment’s program “Prefectures Creating and Demonstrating Low-Cost Hydrogen Models Using Existing Facilities and Infrastructures.”

In this project, electricity generated by a wind turbine system owned by Muroran City is used to produce hydrogen via a water electrolyzer. The hydrogen is stored in cylindrical MH tanks and delivered to consumers through the existing LP gas network. To reduce hydrogen supply costs, it is essential to increase consumption and establish a delivery system for ordinary households and small-scale users. Consumers include households, road heating systems, small shops, accommodation facilities, and metaLProcessing factories. A supply chain is being developed to provide hydrogen fuel cells for households, hydrogen boilers for heat-demanding facilities, and hydrogen gas cutters for factories. To further reduce costs, the project also explores the use of oxygen generated as a by-product from the electrolyzer―which is normally released into the atmosphere―as a resource for land-based aquaculture and for measuring dissolved oxygen levels.

Meiji Electric Industries, a comprehensive electric trading company based in Aichi, Japan, entered the hydrogen business in 2014 and has since established an Engineering Division to promote hydrogen society.The company developed its own pure hydrogen stationary fuel cell generator, "BLUE CLOVER", utilizing Toyota FC modules. To demonstrate this technology, Meiji Electric constructed a green hydrogen utilization facility showcase at its Toyota branch. The facility pioneers a self-consumption and energy storage model: surplus electricity from solar panels on non-working days is used to produce green hydrogen via water electrolysis. This stored hydrogen is then supplied to the "BLUE CLOVER" unit on working days to generate CO2-free electricity for the building. It also serves as a crucial BCP (Business Continuity Plan) power source for a local emergency shelter.The facility is a key demonstration site for performance validation and cost reduction studies. Meiji Electric is leveraging its showcase and participation in national projects (METI/MOE) to accumulate expertise in hydrogen engineering and supply chain construction, aiming to accelerate the nationwide adoption of hydrogen solutions.

Hydrogen storage materials have been mainly considered as a safe hydrogen storage method because of higher volumetric hydrogen density even at lower pressure than 1 MPa at room temperature. In addition, they have other functions such as hydrogen purification, thermal energy storage, and hydrogen compression. They come from selective reactivity with hydrogen, chemical reaction, and thermodynamic stability of hydrides. After hydrogen storage materials absorb hydrogen at room temperature, hydrogen release reaction takes place leading to hydrogen compression when materials are heated. This thermochemical hydrogen compression is one of non-mechanical compression methods and hasbeen considered as an alternative hydrogen compression method for mechanical compressors. In this paper we will introduce our recent research activities for thermochemical hydrogen compression. For such applications, itis important to evaluate hydrogenation properties in wide ranges of pressure and temperature. Therefore, we developed equipment enabling us to evaluate hydrogenation/dehydrogenation properties up to 100 MPa and successfully obtained pressure-composition isotherms up to 100 MPa. For the material development, we focused on quaternary Ti(Cr, Mn, Fe)₂ compounds withvarious chemical compositions. Ternary Ti(Cr, Mn)₂ compounds show higher plateau pressure around 10 MPa at room temperature but the desorption pressure was not reached to 80 MPa at 80℃. However, these compounds show excellent cyclic durability upon pressure swinging and temperature swinging experiments. In order to increase the achievable pressure upon heating, we investigated the effects of Fe substitution on the thermodynamic stabilityoftheirhydride.WithincreaseofFecontent,bothabsorptionanddesorptionpressureincreasedandcompression experiment shows thatthe pressure reached to 80 MPa at 84℃.

Scaling up water electrolyzers for green hydrogen production poses challenges in predicting megawatt- to gigawatt (MW/GW)-class system behavior under renewable energy power fluctuations. A fundamental evaluation is warranted to connect the characteristics of W- to kW-class laboratory electrolyzers with those of MW- to GW-class systems in practical applications. This study evaluates a 50 kW-class proton exchange membrane water electrolyzer with 30 cells using an accelerated degradation test protocol, a simulated renewable energy power and a constant current of 800 A (1.33 A cm^－2), and the results show average degradation rates per cell of 40.4, 27.2, and 5.6 μV h^－1, respectively. Evidently, a voltage as approximate indicator exists for each cell to effectively suppress degradation. Durability tests reveal reductions in anode catalyst loading on the membrane electrode assemblies and inhomogeneous oxidation of the anode current collector. The findings contribute to predicting the stacking performance of electrolyzers for practical applications.

Low-carbon hydrogen is expected to play a significant role in achieving carbon neutrality, as no CO₂ emissions are attributed to its combustion. However, a certain amount of CO₂ emissions can be associated with low-carbon hydrogen from a life cycle perspective, since the energy and material inputs involved in its supply chain ― including production, storage, and transport ― entail CO₂ emissions. This article provides an overview of life cycle assessment, explains its relevance to low-carbon hydrogen, and presents an example of the life cycle CO₂ emissions associated with imported hydrogen to Japan.