Electrocatalytic Activities of La0.6Ca0.4CoO3 and La0.6Ca0.4CoO3-Carbon Composites Toward the Oxygen Reduction Reaction in Concentrated Alkaline Electrolytes

Perovskites exhibit high activities toward oxygen reduction reaction (ORR) in alkaline media, which are the promising candidates for air-cathode in zinc-air rechargeable batteries. Among them, La0.6Ca0.4CoO3-C was reported with high ORR activities in alkaline solutions. However, the functioning of carbon support towards ORR was rare studied. In this study, La0.6Ca0.4CoO3 powder was prepared and characterized by X-ray diffraction, high-resolution transmission electron microscopy, and the Brunauer Emmett Teller gas adsorption technique. The electrocatalytic properties of La0.6Ca0.4CoO3 (LCCO) and La0.6Ca0.4CoO3-carbon composite (LCCO-C) layers towards the ORR were comparatively studied using the rotating ring-disk electrode technique in 1, 4, and 6 M KOH electrolytes to reveal the functioning of carbon. The Koutecky-Levich theory and Tafel slope analysis were applied to acquire the overall electron transfer number and kinetic parameters, such as kinetic currents, rate constants, and exchange current densities. The overall electron transfer number was measured to be almost 4 for both LCCO and LCCO-C. A synergetic effect toward the ORR was observed when carbon was present in the LCCO layer, explained by an assumed 2+2-electron transfer pathway. The ORR activities and kinetics of LCCO-C were better than LCCO, and the synergetic effect (2+2-electron transfer pathway) is proposed as one possible reason. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3560170] All rights reserved.