S-Vacancy Rich Ni-Doped CoS Embedded in S,N Co-doped Carbon as a Bifunctional Catalyst for Zinc–Air Battery

Simultaneously optimizing activities of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) remains challenging in the design of bifunctional electrocatalysts due to their distinct reaction pathways. Herein, a simultaneous sulfidation-carbonization strategy using CoNi-ZIF to construct S-vacancy-rich Ni-doped CoS embedded in an S,N co-doped carbon matrix (Ni-CoS-VS@SNCI) as a self-supported bifunctional electrocatalyst for rechargeable zinc-air batteries (ZABs). The N-configured network facilitates the ORR intermediates' adsorption and promotes a highly selective four-electron ORR pathway. For OER, S vacancies tailor the electronic structure and accelerate electrochemical reconstruction. Combined in situ characterization and density functional theory (DFT) calculations reveal that S-vacancy-induced reconstruction leads to the formation of low-crystalline Co(Ni)OOH with abundant O vacancies, potentially involving the lattice oxygen mechanism (LOM). As a result, Ni-CoS-VS@SNCI delivers a half-wave potential of 0.863 V for ORR and a low overpotential of 289 mV at 20 mA cm-2 for OER. In ZABs, it achieves a high specific capacity of 816 mA h gZn-1 and excellent long-term stability, outperforming commercial Pt/C + RuO2 catalysts. This work provides a viable route for synchronizing dual-site optimization in oxygen electrocatalysis.