Three-dimensional radial α-MnO2 synthesized from different redox potential for bifunctional oxygen electrocatalytic activities

The morphology of manganese dioxides has great effects on their electrocatalytic activities. Herein, two different types of three-dimensional (3D) radial alpha-MnO2 (dandelion- and urchin-like) catalysts are readily fabricated via two different redox reactions through the hydrothermal method, and their electrocatalytic activities are studied for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). As a result, the dandelion-like alpha-MnO2 exhibits a higher electrocatalytic performance than urchin-like alpha-MnO2, with a lower overpotential (20 mV lower for ORR and 90 mV lower for OER), higher mass activity and lower Tafel slope. The excellent electrocatalytic activity of dandelion-like alpha-MnO2 can be attributed to its relatively larger BET and electrochemical active surface area, richer defects, higher amount of Mn3+, and less charge transfer resistance. Our results shed insights into developing new way in constructing the deficient alpha-MnO2 bifunctional oxygen electrocatalysts. (C) 2017 Elsevier B.V. All rights reserved.