The art of balance: Engineering of structure defects and electrical conductivity of α-MnO2 for oxygen reduction reaction

Manganese dioxides have emerged as promising candidates for catalyzing oxygen reduction reaction (ORR). To promote ORR activity, intensive effort has been made to engineer manganese dioxides with either abundant defects or high electrical conductivity. In this work, a balance in engineering between defects and electrical conductivity in controllable engineering of alpha-MnO2 is successfully demonstrated. By controlling the reaction temperature (60, 80, and 140 degrees C), three-dimensional (3D) dandelion-like alpha-MnO2 microspheres were synthesized with different degrees of defects and electrical conductivities. The alpha-MnO2 with either more defects or higher electrical conductivity should possess better ORR performance. However, with increasing synthesis temperature, the defects in the as-prepared samples decreased, while the electrical conductivity increased. Therefore, the preparation alpha-MnO2 at 60 degrees C or 140 degrees C for the best ORR performance remains unclear. As determined by electrochemical measurement, the alpha-MnO2 prepared at 80 degrees C with moderate defects and electrical conductivity exhibits superior ORR performance with a potential of 0.79 V at a current density of -3mA cm(-2), which is considered outstanding for manganese oxides. This work shed new light on the strategy to simultaneously regulate the defect and electrical conductivity, and a balance between them should produce an effective catalyst for ORR. (C) 2018 Elsevier Ltd. All rights reserved.