Hierarchical Co3O4 Microspheres via Dual-Metal Doping-Induced Nanorod Self-Assembly: Toward High-Efficiency Bifunctional Cathode Catalysts for Li-O2 Batteries

Abstract

Spinel-type Co3O4 has been identified as a highly prospective cathode catalyst for lithium-oxygen batteries (LOBs), attributable to its distinctive bimetallic active sites that manifest exceptional bifunctional catalytic characteristics. Nonetheless, the practical implementation of this process is constrained by the inherent conductivity limitations of Co3O4 and the suboptimal utilization of active sites. In this study, a Cu-Mn bimetallic doping strategy is employed to prepare a spherical-like structure of Co3O4 formed by self-assembling one-dimensional nanorods. The introduction of Cu²⁺ results in a reduction of the surface energy of the system, thereby facilitating the directional growth of the nanorods. The redox-active Mn³⁺/Mn⁴⁺ pairs exhibit an inhibitory effect on Ostwald ripening, achieved by stabilizing the fine particles during synthesis and regulating solute diffusion kinetics. This combined action of Cu and Mn enhances active site exposure and optimizes charge transfer kinetics. Furthermore, the doping of bimetallic ions resulted in the redistribution of the Co3+/Co2+ ratio, optimizing the electronic structure for efficient charge transfer during the reaction. The combination of tailored electronic states and optimized nanostructures demonstrates excellent dual-functional catalytic activity for ORR and OER, with a half-wave potential of 0.71 V (vs RHE) for OER and an overpotential of 400 mV (10 mA cm-2) for ORR. The assembled LOBs can be stably cycled up to 450 cycles and an ultra-high discharge capacity of 7268 mAh g-1 for LOBs. This study provides a novel reference for the design of efficient bifunctional catalysts.