| 초록 |
The micro emulsion method has been successfully used for preparing perovskite LaCoO 3 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, LaCoO 3 powder was also prepared by sol-gel method for comparison, with a broad particle distribution and high agglomeration. The electro catalytic properties of LaCoO 3 and LaCoO 3 -carbon Super P mixture layers toward the ORR were studied comparatively using the rotating disk electrode technique in 0.1 M 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 ~3.74 for the LaCoO 3 -Super P mixture, quite close to the theoretical value (4.0), and ~2.7 for carbon-free LaCoO 3 . A synergistic effect toward the ORR is observed when carbon is present in the LaCoO 3 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 LaCoO 3 -Super P mixture, are dominated by a 2+2-electron transfer pathway to form the final, hydroxyl ion product. |
