Spin-State Engineering via Cr3+ Incorporation in Co3O4 Spinel for Efficient Bifunctional Oxygen Electrocatalysis

Abstract

The primary challenge in rechargeable Zn-air batteries lies in developing a catalyst capable of simultaneously improving performance for oxygen reduction reaction (ORR) during discharge and oxygen evolution reaction (OER) during charge. Engineering spin configuration is essential for enhancing the intrinsic bifunctional activity and stability of spinel Co₃O₄. Herein, Cr³⁺ is doped into Co₃O₄, inducing directional distortion of CoO₆ octahedron to modify crystal field splitting energy, pushing Co_Oh toward intermediate-spin (IS) configuration (${t_{2g}}^5{e_g}^1$) with optimized $e_g$ occupancy of 1.04. As a result, 9%Cr-Co₃O₄ demonstrates an excellent bifunctional activity and remarkable rechargeable Zn-air battery performance that even outperforms Pt/C + RuO₂. Density functional theory (DFT) studies reveal that IS Co_Oh not only regulates the adsorption energy of ORR/OER species but also transform the O₂ adsorption configuration from end-on to Griffith configuration, thus modifies the mechanisms of both ORR and OER process and optimize bifunctional activity and selectivity. This work provides mechanistic insight into the spin origin of ORR/OER catalysis and highlights a promising strategy for developing robust bifunctional electrocatalysts.