α-MnO 2 /RuO 2 mixed oxides in the form of sea urchin shaped nanostructures were synthesized in the weight ratio of 82:18 via a simple hydrothermal method. The synthesized α-MnO 2 /RuO 2 urchin nanostructure was constructed with several straight and radially grown nanorods, and composed of homogeneously distributed MnO 2 and RuO 2 nanoparticles. When the α-MnO 2 /RuO 2 nanostructure was applied for air cathode catalyst, it displayed superior cyclic performances of lithium air battery with stable specific capacity, decreased overpotential and good retention rate. The α-MnO 2 /RuO 2 urchin nanostructure exhibited excellent bifunctional electrocatalytic activity for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Linear sweep voltammetry study confirmed that the α-MnO 2 /RuO 2 nanostructure possesses catalytic performance comparable to that of commercial Pt/C for the ORR, while it exhibits lower onset potential and higher limiting current than those of commercial Pt/C for the OER.

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Li–O2 battery offers a dramatic increase in theoretical energy density relative to Li–ion cells, opening up the possibility of electric vehicles and renewable high energy systems. However, the sluggish kinetics at air cathode during discharge and charge processes requires the development of a promising bifunctional electrocatalysts to simultaneously improve the oxygen reduction and oxidation (ORR and OER) kinetics, resulting in increased reversibility of the battery. In this work, three dimensional (3D) α–MnO2/RuO2 mixed oxides at different ratios were synthesized using a simple hydrothermal method. The 3D mixed oxides were designed to be applied as suitable bifunctional electrocatalysts for Li–O2 batteries. 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 bifunctional catalytic properties were analyzed using oxygen reduction and evolution reactions (ORR and OER) in a rotating ring disc electrode system. It was found that α–MnO2 and RuO2 significantly served as ORR and OER catalysts, respectively, confirming that the mixed oxide is a suitable 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 α–MnO2/RuO2 (75:25) could 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 a maximum capacity of >8100 mAh g-1 with high columbic efficiency and cyclability.