Manganese Dioxide-based Bifunctional Oxygen Reduction/Evolution Electrocatalysts: Effect of Perovskite Doping and Potassium Ion Insertion

Non-precious metal bifunctional oxygen reduction and oxygen evolution reaction (ORR and OER, respectively) catalysts are of great interest for rechargeable metal/air batteries and regenerative alkaline fuel cells. We investigate the initial stage activities and the electrocatalytic durability of bifunctional catalysts composed of MnO2 and perovskite (LaNiO3 or LaCoO3) in a 1:1 weight ratio. Gas diffusion electrodes (GDE) with a catalyst layer composed of MnO2:co-catalyst (LaNiO3 or LaCoO3):Vulcan XC-72 were prepared and studied in O-2 saturated 6 M KOH. The initial stage bifunctional activities of MnO2-LaCoO3 and MnO2-LaNiO3 are markedly superior compared to either MnO2 or perovskite alone, demonstrating a synergistic effect. Furthermore, we show for the first time that the degradation of the bifunctional electrocatalytic activity of the MnO2-perovskite electrodes during extensive potential cycling can be fully restored by resting the electrodes at open-circuit potential in 6 M KOH. A hypothesis is proposed to explain this catalytic promotion and 'healing' effect based on XPS results showing potassium ion incorporation in the electrocatalyst structure. Lastly, a thorough comparison of the results obtained in the present work with those reported in the literature with a variety of bifunctional catalysts is presented, demonstrating the effectiveness of the MnO2-perovskite electrodes. (C) 2014 Elsevier Ltd. All rights reserved.