Ultrathin two-dimensional electrocatalysts: Structure-property relationships, mechanistic insights, and applications in water electrolysis

The pursuit of sustainable hydrogen production has positioned water electrolysis as a cornerstone technology for global carbon neutrality. However, sluggish kinetics, catalyst scarcity, and system integration challenges hinder its widespread deployment. Ultrathin two-dimensional (2D) materials, with their atomically exposed surfaces, tunable electronic structures, and defect-engineering capabilities, present unique opportunities for next-generation electrocatalysts. This review provides an integrated overview of ultrathin 2D electrocatalysts, discussing their structural diversity, synthetic routes, structure-activity relationships, and mechanistic understanding in water electrolysis processes. Special focus is placed on the translation of 2D materials from laboratory research to practical device implementation, emphasizing challenges such as scalable fabrication, interfacial engineering, and operational durability in realistic electrolyzer environments. The role of advanced characterization techniques in capturing dynamic structural changes and active site evolution is discussed. Finally, we outline future research directions, emphasizing the synergy of machine learning-driven materials discovery, advanced operando characterization, and scalable system integration to accelerate the industrial translation of 2D electrocatalysts for green hydrogen production.