Regulating electronic structure of CoN₄ with axial Co–S for promoting oxygen reduction and Zn-air battery performance

Regulating the coordination environment of transition-metal based materials in the axial direction with heteroatoms has shown great potential in boosting the oxygen reduction reaction (ORR). The coordination configuration and the regulation method are pivotal and elusive. Here, we report a combined strategy of matrix-activization and controlled-induction to modify the CoN₄ site by axial coordination of Co–S (Co₁N₄-S₁), which was validated by the aberration-corrected electron microscopy and X-ray absorption fine structure analysis. The optimal Co₁N₄-S₁ exhibits an excellent alkaline ORR activity, according to the half-wave potential (0.897 V vs. reversible hydrogen electrode (RHE)), Tafel slope (24.67 mV/dec), and kinetic current density. Moreover, the Co₁N₄-S₁ based Zn-air battery displays a high power density of 187.55 mW/cm² and an outstanding charge–discharge cycling stability for 160 h, demonstrating the promising application potential. Theoretical calculations indicate that the better regulation of CoN₄ on electronic structure and thus the highly efficient ORR performance can be achieved by axial Co–S.