Rational Design of Single-Atom Catalysts for the Hydrogen Evolution Reaction for Advancing Sustainable Energy Conversion and Storage

Progress in sustainable hydrogen production requires electrocatalysts that accelerate the hydrogen evolution reaction (HER) with excellent catalytic activity and durability. Single-atom catalysts (SACs) have gained attention as superior HER electrocatalysts because of their almost 100% atomic utilization, distinct coordination surroundings, and tunable electronic structures. This review surveys advances in HER SACs with emphasis on atomic-level engineering and catalytic mechanisms. We first explore the fundamental principles and reaction mechanisms of the HER. The morphological engineering of numerous SAC architectures is discussed, along with their structural features and roles in boosting HER performance. The structural characteristics of SACs are examined to explain the roles of orbital interactions, charge redistribution, local structural asymmetry, and metal–support interactions in regulating hydrogen adsorption and HER kinetics. Finally, the catalytic performance of several SAC structures is discussed extensively, with a focus on HER activity, reaction kinetics, and prolonged stability. Density functional theory (DFT) is used to elucidate the mechanism underlying the outstanding catalytic performance of SACs in the HER. Moreover, key challenges associated with scalability, catalyst stability, and long-term operation at practical current densities are discussed, and future research directions are proposed. Finally, we discuss the rational development of next-generation SACs toward sustainable hydrogen production.