Micro Emulsion Synthesis of LaCoO3 Nanoparticles and their Electrochemical Catalytic Activity

The micro emulsion method has been successfully used for preparing perovskite LaCoO3 with uniform, fine-shaped nanoparticles showing high activity as electro catalysts in oxygen reduction reactions (ORRs). They are, therefore, promising candidates for the air-cathode in metal-air rechargeable batteries. Since the activity of a catalyst is highly dependent on its specific surface area, nanoparticles of the perovskite catalyst are desirable for catalyzing both oxygen reduction and evolution reactions. Herein, LaCoO3 powder was also prepared by sol-gel method for comparison, with a broad particle distribution and high agglomeration. The electro catalytic properties of LaCoO3 and LaCoO3-carbon Super P mixture layers toward the ORR were studied comparatively using the rotating disk electrode technique in 0.1M KOH electrolyte to elucidate the effect of carbon Super P. Koutecky-Levich theory was applied to acquire the overall electron transfer number (n) during the ORR, calculated to be similar to 3.74 for the LaCoO3-Super P mixture, quite close to the theoretical value (4.0), and similar to 2.7 for carbon-free LaCoO3. A synergistic effect toward the ORR is observed when carbon is present in the LaCoO3 layer. Carbon is assumed to be more than an additive, enhancing the electronic conductivity of the oxide catalyst. It is suggested that ORRs, catalyzed by the LaCoO3-Super P mixture, are dominated by a 2+ 2-electron transfer pathway to form the final, hydroxyl ion product.