Sustainable hydrogen production via metal–water reactions and transition metal nitride electrocatalysts: A pathway toward green energy

• Metal waste like Al, Mg, Zn, and Fe enables eco-friendly hydrogen production. • Hydrogen yield varies with metal type, medium, and catalytic pre-treatment. • TMNs offer stable, low-cost electrocatalysis for hydrogen evolution reaction. • TMNs excel in conductivity, activity, and durability for HER applications. • Coupling metal waste and TMNs enables scalable, green hydrogen technologies. Hydrogen is increasingly recognized as a vital element in the global transition toward clean and sustainable energy systems. This review highlights recent advances in hydrogen generation via the reaction of metals—particularly scrap metals—with water, presenting a cost-effective and environmentally friendly alternative to conventional production methods. The hydrogen yield largely depends on the metal's reactivity. Highly reactive metals such as lithium and sodium generate hydrogen with minimal energy input, whereas less reactive metals like aluminum and magnesium require elevated temperatures to achieve yields. Remarkably, hydrogen yields of up to 98 % have been reported with aluminum, while metals such as zinc yield substantially lower outputs under more demanding conditions. To achieve the necessary hydrogen purity for practical applications, additional purification processes—including membrane-based separation, pressure swing adsorption, and cryogenic distillation—are essential. The review also explores the emerging role of transition metal nitrides (TMNs) in hydrogen evolution reactions (HER). TMNs are gaining attention as cost-effective, efficient alternatives to platinum-based catalysts due to their high electrical conductivity, chemical stability, and catalytic activity. However, challenges remain in optimizing their active surface area, enhancing cycle durability, and developing scalable, reproducible synthesis techniques. Furthermore, elucidating the relationship between TMN structural features and their catalytic behavior—particularly under neutral pH conditions—is critical for advancing their application. The integration of metal-assisted hydrogen generation with TMN-based electrocatalysis represents a compelling pathway toward high-efficiency, low-cost, and sustainable hydrogen production. This synergistic approach holds significant for powering a wide range of technologies, from fuel cells to industrial energy systems.