Abstract
<jats:p> Green hydrogen production through water electrolysis is a cornerstone technology for decarbonization, yet its widespread deployment hinges on the development of electrocatalysts that simultaneously deliver high activity, long-term stability at industrially relevant current densities (>500 mA cm <jats:sup>-2</jats:sup> ), and economic viability. This review critically examines recent advances in electrocatalytic materials for the HER and OER, spanning noble-metal, transition-metal oxide/hydroxide/chalcogenide/phosphide, high-entropy, single- and dual-atom, and perovskite/spinel families. The unifying design levers defect/vacancy engineering, electronic/geometric coupling between metal centers, and periodic/templated site ordering that recur across chemistries and operating environments (acidic, alkaline, and seawater) are particularly emphasized. Catalyst stability and degradation mechanisms are analyzed in depth, along with membrane-electrode assembly engineering, scalable synthesis routes, impurity tolerance, and hybrid electrolysis strategies. Techno-economic and life-cycle considerations are integrated throughout, highlighting the importance of weighing overpotential reduction against manufacturability, elemental abundance, stack-level integration, and environmental footprint. Key gaps, including the lack of standardized high-current-density testing protocols and insufficient focus on real-feedstock performance, are identified, and concrete recommendations are provided. By bridging fundamental materials chemistry with device-level and system-level considerations, this review charts pathways for translating laboratory discoveries into gigawatt-scale green hydrogen production. </jats:p>