Synergistic LaCoO3@Co3O4 bifunctional catalyst for efficient oxygen evolution and reduction: achieving low polarization

Abstract

Lithium–oxygen batteries (LOBs) suffer from low cycle stability and limited capacity primarily due to the sluggish kinetics of the oxygen evolution reaction (OER) and the oxygen reduction reaction (ORR). To address this and develop high-performance air cathodes, we systematically synthesized a series of metal oxide catalysts (Co₃O₄ (CO), LaCoO₃ (LCO), and LaCoO₃_Co₃O₄ (LCO_CO)) using a coprecipitation method and evaluated their bifunctional catalytic activities for OER and ORR in an alkaline electrolyte. Among the synthesized materials, the LCO_CO composite catalyst demonstrated superior bifunctional activity, achieving the lowest potential gap (ΔE) of 1.14 V between the OER and ORR. Intriguingly, this exceptional performance was achieved despite LCO_CO exhibiting the lowest electrochemical surface area (ECSA) value. These findings strongly indicate that the catalytic performance was governed not by the macroscopic quantity of the surface area, but by qualitative factors such as the structure and electronic state of the atomic-level active sites (i.e., intrinsic activity). Structural analyses by XRD and XPS suggested that the homogeneous compounding, coupled with the incorporation of Co²⁺ ions during synthesis, induced defects (possibly La site vacancies), leading to a significant increase in lattice oxygen vacancies and an optimization of the Co³⁺/Co²⁺ ratio. Electronic structure investigations further revealed that these synergistic structural and electronic modifications narrowed the energy gap between the Co 3d and O 2p band centers, thereby reducing the charge transfer energy. This modulation not only optimizes the adsorption of oxygenated intermediates but also facilitates the participation of lattice oxygen via the Lattice Oxygen Mechanism (LOM). We concluded that these interfacial synergistic structural and electronic modifications critically facilitated electron transfer during the OER/ORR processes, contributing to the observed exceptional performance. This study provides crucial guidance for designing high-performance composite oxide catalysts for LOBs, emphasizing that qualitative control of active site structure and electronic coupling is key over purely quantitative surface area maximization.