Electrocatalysts for hydrogen energy conversion: fundamental mechanisms, design principles, advances and perspectives

Hydrogen electrocatalysis is central to water electrolysis and fuel-cell technologies, yet its practical development remains hindered by sluggish reaction kinetics, reliance on scarce noble metals, activity-stability trade-offs, limited scalable synthesis, incomplete mechanistic understanding, and inconsistent evaluation protocols. These challenges are particularly evident in the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), hydrogen oxidation reaction (HOR), and oxygen reduction reaction (ORR), where improving intrinsic activity often conflicts with long-term stability, cost reduction, and device-level applicability. This review systematically summarizes fundamental mechanisms, design principles, and recent advances in efficient electrocatalysts, including noble-metal, low-noble-metal, non-noble-metal, and metal-free materials, with emphasis on nanostructure design, active-site and coordination engineering, geometric and electronic structure regulation, heterointerface construction, interfacial microenvironment control, and single-atom catalysis. Advanced in-situ/operando characterization techniques coupled with theoretical calculations are discussed to guide catalyst design, elucidate catalytic mechanisms, and establish reliable structure–performance relationships. Particular attention is given to scalability, stability under industrial conditions, mechanistic perception, standardized benchmarking, and device-level validation. Finally, future perspectives are outlined to guide the development of next-generation electrocatalysts that combine high intrinsic activity, exceptional stability, economic viability, and practical applicability, thereby accelerating the large-scale implementation of hydrogen energy technologies.