Operando Hydroxylation of the Sn–Co Diatomic Catalyst Boosting Ultrastable Zn–Air Batteries

Diatomic catalysts (DAs) exhibit superior catalytic activity for the oxygen reduction reaction (ORR) due to the synergistic interplay between dual metals. However, their dynamic evolution remains unexplored under the working conditions. Herein, Sn–Co diatomic pairs on N-doped carbon with an asymmetric N3Sn–CoN3 structure (SnCoN6 DA) are rationally designed for promoting ORR activity and durability. The operando hydroxylation of SnCoN6 DA regulates O2 adsorption on Co, allowing more d orbitals to hybridize with O2 s/p orbitals. Furthermore, the *OH–Sn moiety serves as an electron modulator that upshifts the d-band center of Co, enabling stronger binding with *OOH and expediting subsequent O–O cleavage. Accordingly, the operando hydroxylation of SnCoN6 DA positively shifts the half-wave potential by 54 mV and enhances the kinetic current density by 16.1 times compared to those of the Co single-atom catalyst. The constructed Zn–air battery shows an ultralong cycling life span (more than 3650 h at 5 and 10 mA cm–2).