Tailoring three dimensional α-MnO2/RuO2 hybrid nanostructure as prospective bifunctional catalyst for Li-O2 batteries

We have synthesized three dimensional architectural alpha-MnO2/RuO2 hybrid nanostructures with three different compositions of (75:25), (69:31) and (50:50) by hydrothermal approach and evaluated their bifunctional electrocatalytic activity for Li-O-2 battery applications. The morphology of the alpha-MnO2/RuO2 nanostructures changed from sharp sea urchins to solid nanospheres with increasing RuO2 content in the composition. The variations observed in physical, structural, morphological and electrochemical properties were characterized with respect to the MnO2/RuO2 concentrations by step by step analyses. MnO2 exhibited better ORR catalytic activity, while RuO2 revealed superior OER catalytic activity. Among the concentrations investigated, alpha-MnO2:RuO2 (75:25) exhibited superior catalytic activity for oxygen reduction and evolution reactions in aqueous media. This excellent catalytic activity logically led us to apply it as air-cathode catalyst in Li-O-2 cell, which produced a maximum capacity of >8100 mAhg (1) with high columbic efficiency and cyclability. The superior performance of the hybrid nanostructure is mainly attributed to its structural and compositional design which favors the electrochemical activity. Based on a careful investigation on the structural characterizations, the growth mechanism of the 3D nanostructured alpha-MnO2/RuO2 mixed oxides is discussed in detail. (C) 2016 Published by Elsevier Ltd.