Advances of earth-abundant cobalt-based single-atom catalysts for acidic oxygen evolution by electrolysis

The oxygen evolution reaction (OER) is critical for sustainable energy technologies, including proton exchange membrane water electrolyzers (PEMWEs) and metal-air batteries. However, its implementation in acidic media remains constrained by sluggish kinetics, high energy barriers, and reliance on scarce noble-metal catalysts. Cobalt-based single-atom catalysts (Co-SACs) have emerged as a breakthrough solution, combining exceptional catalytic activity, stability, and atomic utilization efficiency. Its superior acidic OER performance stems from the electronic structure of low-spin Co³⁺ centers, which optimize t_2g–π orbital interactions with oxygen intermediates. This configuration promotes efficient surface reconstruction and thermodynamically favorable adsorption of OER species, accelerating reaction kinetics. Tailored coordination environments, engineered via supports like nitrogen-doped carbons, graphene, or metal oxides, can further modulate Co electronic and spin states, enhancing activity and durability. This review systematically analyzes advancements in Co-SAC design, elucidating correlations between atomic coordination, electronic properties, and catalytic mechanisms. Advanced synthesis methods and characterization tools are evaluated to discuss structure-activity relationships of Co-SAC. Finally, we address current challenges and future research directions that involve computational modeling, multi-metallic SAC architectures, and operando techniques to guide the rational design of high-performance Co-SACs. Addressing these challenges will accelerate the commercialization of PEMWEs for cost-effective green hydrogen production.