Manipulating the metal–oxygen covalency through diminishing d-p band center difference for rechargeable zinc-air batteries

Abstract

Transition metal oxides have garnered significant attention as electrocatalysts for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). However, their sluggish reaction kinetics and poor stability hinder commercial applications. Herein, we report the synthesis of a bimetallic cobalt manganese oxide, Co_0.99Mn_2.01O₄ (CMO), synthesized via a hydrothermal technique, which serves as a highly efficient bifunctional ORR/OER electrocatalyst owing to its impressive half-wave potential of 0.767 V and low overpotential of 1.677 V at 10 mA cm⁻². Theoretical calculations revealed that the d-band centers of Co 3d and Mn 3d in CMO, located at tetrahedral and octahedral sites, are positioned near the Fermi level, facilitating the adsorption of electrocatalytic intermediates. Furthermore, the distance between the Co 3d and O 2p band centers in CMO is smaller than that in Co₃O₄, and the distance between the Mn 3d and O 2p band centers in CMO is shorter than that in Mn₂O₃, indicating that the Co–O and Mn–O bonds in CMO exhibit greater covalency, significantly enhancing ORR/OER activity. Notably, CMO serves as an advanced air electrode material for rechargeable zinc-air batteries (ZABs), demonstrating improved charge–discharge performance with a low voltage gap of 0.87 V at 5 mA cm⁻², high peak power density of 124 mW cm⁻², and excellent cycle stability of over 540 h at 5 mA cm⁻². This superior ORR/OER activity, combined with the simple material combination, makes CMO a promising catalyst for rechargeable ZABs.

Graphical Abstract