γ-MnO2 nanorod-assembled hierarchical micro-spheres with oxygen vacancies to enhance electrocatalytic performance toward the oxygen reduction reaction for aluminum-air batteries

gamma-MnO2 nanorod-assembled hierarchical micro-spheres with abundant oxygen defects are synthesized by a simple thermal treatment approach as oxygen reduction electrocatalysts for Al (aluminum) air batteries. The rich oxygen vacancies on the surface of gamma-MnO2 are verified by morphology, structure, electron paramagnetic resonance (EPR) and X-ray photoelectron spectroscopy (XPS) results. The oxygen reduction reaction (ORR) electrocatalytic activity of gamma-MnO2 is significantly improved by the incoming oxygen vacancies. The gamma-MnO2 nanorod-assembled hierarchical micro-spheres calcined under 300 degrees C in Ar atmosphere show the best ORR performance. The primary Al-air batteries using gamma-MnO2 catalysts as the cathode, which demonstrates excellent peal power density of 318 mW cm(-2) when applying the gamma-MnO2 catalysts with optimal amount of oxygen vacancies. (c) 2020 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. and Science Press. All rights reserved.