Electronic Structure\nModulation Induced by the Synergy\nof Cobalt Low-Nuclearity Clusters and Mononuclear Sites for Efficient\nOxygen Electrocatalysis

The\ndevelopment of high-performance bifunctional single-atom\ncatalysts\nfor use in applications, such as zinc–air batteries, is greatly\nimpeded by mild oxygen reduction and evolution reactions (ORR and\nOER). Herein, we report a bifunctional oxygen electrocatalyst designed\nto overcome these limitations. The catalyst consists of well-dispersed\nlow-nuclearity Co clusters and adjacent Co single atoms over a nitrogen-doped\ncarbon matrix (Co<sub>SA+C</sub>/NC). The precisely tailored asymmetric\nelectronic structures are achieved with strong electronic interactions\nbetween these Co species. The Co clusters optimize the adsorption/desorption\nstrength of oxygenated intermediates on single-atomic Co sites to\nendow exceptional activity under alkaline conditions with a half-wave\npotential (<i>E</i><sub>1/2</sub>) of 0.91 V and an overpotential\n(η) of 340 mV at 10 mA cm<sup>–2</sup>. In addition,\na zinc–air battery assembled with Co<sub>SA+C</sub>/NC achieves\na high power density of 284.1 mW cm<sup>–2</sup> and a long\noperational lifespan of 400 h, superior to those of the benchmark\nPt/C + RuO<sub>2</sub>. Experimental findings and theoretical analysis\nreveal that the enhanced bifunctional activity stems from the synergistic\ninteractions between Co clusters and single-atomic Co sites. Consequently,\nthe overbinding of *OH is suppressed with accelerated *OH removal.\nThis work establishes the design principle of advanced electrocatalysts\nwith multiphase metal species bearing strong electronic interactions.