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.