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⁺ may play a pivotal role in the regulation of surface energy, thereby facilitating the directional growth of the nanorods. The presence of Mn³⁺/Mn⁴⁺ may be significant in stabilizing the crystal structure, impeding the migration and dissolution of ions, and consequently postponing the Ostwald ripening process. 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 the ORR and OER, with a half-wave potential of 0.71 V (vs. RHE) for the OER and an overpotential of 400 mV (10 mA cm⁻²) for the ORR. The assembled LOBs can be stably cycled up to 450 cycles, exhibiting an ultra-high discharge capacity of 7268 mAh g⁻¹. This study provides a novel reference for the design of efficient bifunctional catalysts.