Introduction and Research Trends in Hydrogen Storage Alloys for Solid-state Hydrogen Storage

Global efforts toward carbon neutrality have accelerated the development of hydrogen as a promising energy carrier. Nevertheless, safe and efficient hydrogen storage remains a major technological bottleneck for realizing a hydrogen-based energy infrastructure. Among various storage methods, solid-state hydrogen storage using metal hydrides has gained significant attention owing to its high volumetric density, reversibility, and superior safety compared with compressed or cryogenic systems. This review summarizes the thermodynamic and kinetic principles governing hydrogen absorption and desorption in metal hydrides and classifies representative systems based on their crystal structures and reaction mechanisms. Particular focus is placed on Ti-, V-, and Mg-based alloys, which exhibit favorable equilibrium pressures, high storage capacities, and compositional tunability. Recent advances in alloying design, phase control, and nanostructural modification have improved reaction kinetics and cyclic stability, while mitigating issues such as high plateau pressure, hysteresis, and activation barriers. In addition, conventional processing routes―casting, powder metallurgy, and extrusion―are re-evaluated for their cost-effectiveness and compatibility with large-scale production. Overall, metal hydrides remain among the most promising materials for solid-state hydrogen storage, and continued progress in alloy design and process optimization is expected to enable practical, safe, and sustainable hydrogen energy systems.