Electronic Structure Modulation Induced by the Synergy of Cobalt Low-Nuclearity Clusters and Mononuclear Sites for Efficient Oxygen Electrocatalysis

The development of high-performance bifunctional single-atom catalysts for use in applications, such as zinc-air batteries, is greatly impeded by mild oxygen reduction and evolution reactions (ORR and OER). Herein, we report a bifunctional oxygen electrocatalyst designed to overcome these limitations. The catalyst consists of well-dispersed low-nuclearity Co clusters and adjacent Co single atoms over a nitrogen-doped carbon matrix (Co_SA+C/NC). The precisely tailored asymmetric electronic structures are achieved with strong electronic interactions between these Co species. The Co clusters optimize the adsorption/desorption strength of oxygenated intermediates on single-atomic Co sites to endow exceptional activity under alkaline conditions with a half-wave potential (E_1/2) of 0.91 V and an overpotential (η) of 340 mV at 10 mA cm^-2. In addition, a zinc-air battery assembled with Co_SA+C/NC achieves a high power density of 284.1 mW cm^-2 and a long operational lifespan of 400 h, superior to those of the benchmark Pt/C + RuO₂. Experimental findings and theoretical analysis reveal that the enhanced bifunctional activity stems from the synergistic interactions between Co clusters and single-atomic Co sites. Consequently, the overbinding of *OH is suppressed with accelerated *OH removal. This work establishes the design principle of advanced electrocatalysts with multiphase metal species bearing strong electronic interactions.