Zeolitic Imidazolate Framework-Derived Bifunctional CoO-Mn3O4 Heterostructure Cathode Enhancing Oxygen Reduction/Evolution via Dynamic O-Vacancy Formation and Healing for High-Performance Zn-Air Batteries

Abstract

Zn-air batteries (ZABs) are promising electrochemical energy storages for many applications, yet their performance is limited by their cathode's poor activity and reversibility for oxygen evolution reaction (OER) in charge and oxygen reduction reaction (ORR) in discharge. Herein, we report a bifunctional CoO-Mn₃O₄ heterostructure (CMH) cathode synthesized from an Mn-doped zeolitic imidazolate framework as a solution to these challenges. Combined machine learning-augmented density functional theory simulations and operando differential electrochemical mass spectrometry with ¹⁸O isotope labeling reveal dynamic O-vacancy (O_v) formation through OH^- desorption from Mn sites during ORR or bidentate oxygen adsorption at Mn-Mn sites during OER, with dynamic O_v healing through OH^- adsorption and deprotonation. This dynamic process lowers O* binding energy to activate the lattice oxidation mechanism for efficient OER/ORR, exhibited by record-low overpotential and stable operation over 2000 cycles for OER and a diffusion-limited current density of 7.1 mA·cm^-2 surpassing Pt/C (5.0 mA cm^-2) for ORR. Moreover, the ZAB with the CMH cathode benefits from an ideal open-circuit voltage (1.43 V) and a high capacity of 802 mAh·g^-1 (97.8 % of theoretical), to achieve its record-high energy density (898 Wh·kg^-1), ultrahigh peak-power density (394.2 mW·cm^-2), and stability with negligible voltage degradation over 600 cycles.