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 in metal-air batteries, and can be comparable to Pt/C. But the low catalytic activity of oxygen evolution reaction 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 selective dissolution method. The core of La0.7Sr0.3MnO3 particle 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 electrocatalyst for metal-air batteries. Based on results of transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), valence band spectrum and O2 temperature programmed desorption (O2-TPD) 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 LSM core and MnO2 shell. It can be attributed to three aspects: a) the electronic conductivity, which is beneficial to provide the faster charge transfer paths and kinetics in the oxide/solution interface than that of 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; c) the tuning of oxygen adsorption ability via the moderate Mn-O bond strength, which may be conducive to getting an enhanced Mn-O bond on the surfaces for ORR and a weaken Mn-O bond in the lattice for OER.