Breaking the symmetry and d-orbital optimization at Co site in CoNC as bifunctional air catalysts for rechargeable liquid and flexible solid-state Zn-air batteries

By utilizing abundant earth metals and incorporating them into N-doped carbon electrocatalysts, the electrochemical kinetics and stability of oxygen reactions in zinc-air batteries (ZABs) are enhanced. However, several challenges remain. We introduce a method that focuses on microenvironmental modulation to precisely adjust the Cr-doped Co NC (Cr-Co NC) catalyst, thereby enhancing its inherent electrochemical activity and durability, and improving the oxygen reaction process. The unique Cr-N-Co configuration in the Cr-CoNC-1.00 catalyst weakens the adsorption strength of *OH intermediates by engineering the Co d-band center, thus lowering the energy barrier for both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). The precisely engineered Cr-CoNC-1.00 catalyst demonstrates robust ORR and OER performance, achieving an ORR half-wave potential (E_1/2) of 0.865 V and an OER overpotential (E_J=10) of 1.64 V (vs RHE), rivaling that of noble-metal catalysts (Pt/C for ORR and RuO₂ for OER). In practical applications, the rechargeable liquid ZABs equipped with Cr-CoNC-1.00 delivered exceptional results (peak power density: 110 mW·cm^-2, specific capacity: 816 mA·h·g^-1 Zn at 10 mA·cm^-2, with over 208 h of charge-discharge cycle stability). Additionally, the flexible solid-state ZABs achieved an open-circuit voltage of 1.4 V, demonstrated remarkable charge-discharge stability for over 12 h, and maintained performance under various bending conditions. This approach highlights the significant potential for developing high-efficiency bifunctional catalysts suitable for flexible zinc-air batteries.