Integrated Single‐Atom and Cluster Catalysts for Electrocatalytic Hydrogen Energy Technologies: Current Achievements and Challenges

Hydrogen energy is crucial for global carbon neutrality, relying on efficient green hydrogen electrolysis and fuel cells. However, sluggish kinetics in key electrocatalytic reactions, that is, oxygen evolution reaction (OER), hydrogen evolution reaction (HER), and oxygen reduction reaction (ORR), and dependence on scarce platinum-group metals hinder their viability. Single-atom catalysts offer high atom utilization but lack multi-site synergy for complex reactions like OER and certain HER pathways. Atomically precise clusters enable multi-electron processes but suffer from electrochemical instability. Integrated single-atom and cluster catalysts (ISACCs) overcome these limitations by creating synergistic interfaces. This synergy significantly enhances activity, selectivity, and stability for core hydrogen reactions (HER, OER, ORR, HOR), reducing dependence on platinum-group metals. This review begins with introducing ISACC design strategies, synthesis methods, and performance breakthroughs in these four critical reactions. Then we analyze the atom-cluster enhancement mechanisms and finally discuss challenges and future directions, aiming to guide the development of efficient, stable, and low-cost electrocatalysts and promote their practical application in hydrogen energy technologies.