Growth and Electrochemical Characterization of Sea Urchin Shaped α-MnO2/RuO2 Mixed Oxides for Cathode Catalyst Application in Lithium–Oxygen Battery

Abstract

For the further advancement of lithium air battery, the design of a new promising bifunctional electrocatalyst is necessary to improve oxygen reduction and evolution reactions (ORR and OER) kinetics during discharge and recharge processes. In this work, three dimensional (3D) α–MnO2/RuO2 mixed oxides were designed and synthesized using simple hydrothermal method. The morphology of the mixed oxides changed from sea urchin shaped nanostructures to nanospheres with the increase of RuO2 content in the mixed oxides. The growth mechanism of the mixed oxides have been studied by analyzing their step by step growth and development through various characterization techniques such as x-ray diffraction, scanning electron microscopy, transmission electron microscopy (TEM), cross sectional TEM and electron dispersive spectrum, etc. It was found that α–MnO2 and RuO2 significantly served as oxygen reduction and evolution reaction catalysts, respectively, indicating that the mixed oxide is suitable as bifunctional catalyst for Li–O2 battery. Among the four different α–MnO2/RuO2 composition ratios, (75:25) appeared to be the optimum ratio for the mixed oxides with superior activity for both ORR and OER. The superior performance of (75:25) ratio can be attributed to its structural and compositional design which aid in the better catalytic performance. When applied in Li–O2 battery system, the (75:25) ratio exhibited excellent performance with maximum capacity of >8100 mAh/g, high coulombic efficiency and cyclability.