Electronic Delocalization Regulates the Occupancy and Energy Level of Co 3dz2 Orbitals to Enhance Bifunctional Oxygen Catalytic Activity

Abstract

AbstractCobalt–nitrogen–carbon is hitherto considered as one of the most satisfactory alternatives to precious metal catalysts for oxygen electrocatalysts. However, precisely tuning the local coordination of Co sites and thus engineering d‐orbital electron configuration to optimize the binding energy of the intermediates remains a huge challenge. Herein, a robust electrostatic self‐assembly strategy is developed to engineer penta‐coordinated Co sites by introducing axial O ligands with atomic‐level precision to form CoN4O1 configurations on MXene nanosheets (CoN4‐O/MX). The optimized CoN4‐O/MX demonstrates outstanding bifunctional electrocatalytic performance with a small potential gap of 0.72 V, significantly outperforming the cobalt–nitrogen–carbon catalyst with plane‐symmetric CoN4 sites and precious metal counterparts. The Zn–air batteries integrated with CoN4‐O/MX provide an outstanding peak power density of 182.8 mW cm−2 and a long‐term cyclability for 250 h. Density functional theory calculations reveal that CoO coordination induces electronic delocalization to draw off partial electrons from the dz2 orbital, which forms unsaturated orbital filling and lifts the energy level, resulting in a stronger Lewis basicity to facilitate electron injection into the intermediate. The study presented here provides not only a novel methodology to achieve precise control of heteroatom coordination, but also a fundamental understanding about the structure–activity relationships of dz2 orbitals.