Enhanced Bifunctional Catalytic Activity of Manganese Oxide/Perovskite Hierarchical Core–Shell Materials by Adjusting the Interface for Metal–Air Batteries

LaMnO3 perovskite is one of the most promising catalysts for oxygen reduction reaction (ORR) in metal–air batteries and can be compared to Pt/C. However, the low catalytic activity toward oxygen evolution reaction (OER) limits its practical application in rechargeable metal–air batteries. In this work, the MnO2/La0.7Sr0.3MnO3 hierarchical core–shell composite materials with a special interface structure have been designed via the selective dissolution method. The core of La0.7Sr0.3MnO3 particles is wrapped by the porous and loose MnO2 nanoparticles. The as-prepared MnO2/La0.7Sr0.3MnO3 materials have excellent catalytic activity toward ORR/OER and are used as bifunctional oxygen electrocatalysts for metal–air batteries. Based on results of transmission electron microscopy, X-ray photoelectron spectroscopy, valence-band spectroscopy, and O2 temperature-programmed desorption analysis, we conclude that the bifunctional catalytic activity of the MnO2/La0.7Sr0.3MnO3 materials can be effectively promoted due to the specific interface structure between the La1–xSrxMnO3 core and the MnO2 shell. This can be attributed to three aspects: (a) the electronic conductivity, which is beneficial for providing the faster charge-transfer paths and kinetics at the oxide/solution interface than that of the MnO2 sample; (b) the enhancement of oxygen adsorption capacity due to surface defects (oxygen vacancies) and chemical adsorption, which is helpful to improve the reaction kinetics during the process of oxygen catalysis; and (c) the tuning of oxygen adsorption ability via the moderate Mn–O bond strength, which may be conducive to getting for obtain an enhanced Mn–O bond strength on the surfaces for ORR and a weakened Mn–O bond in the lattice for OER.