Study on the Effect of Surface Area on the Oxygen Reduction Reaction Performance of Perovskite Catalyst for Lithium-Oxygen Batteries

摘要

Lithium oxygen batteries have been recognized as one of the next-generation power sources, capable of supplying power for a long time even in an independent extreme environment. In spite of the theoretical advantage, Li-O_2 batteries face technical and economic challenges that must be addressed to promote them as commercially variable technologies for future energy system. Above all, battery performance largely depends on the activities of the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) of the cathode during discharge and charge, respectively. The undesirable overpotential caused by sluggish reaction kinetics associated with the ORR and OER greatly limit the current performance of Li-O_2 batteries, which must be improved by efficient catalyzing the reactions. Among the numerous catalysts, perovskite oxides have attention for candidate electro catalyst for Li-O_2 batteries due to their high electronic/ionic conductivity, high electrochemical stability, and catalytic activity. Especially, La_(0.6)Sr_(0.4)Co_(0.2)Fe_(0.8)O_3(LSCF) is considered as a typical catalyst for Li-O_2 batteries, which can provide high oxygen surface exchange coefficient for fast kinetics at the gas/electrode interface. The surface area is significantly related on the ORR and OER performance, which influences on the active area for reactions. In this study, we have tried to utilize a simple high energy ball milling process to investigate the electrochemical properties of LSCF catalyst. Through the BET analysis, it was confirmed that the specific area significantly was increased after ball milling due to the reduced particle size, obtaining the optimized milling time with the higher ORR performance. The electrochemical activities have been measured with rotating disk electrode (RRDE) method. Well-ball milled LSCF catalyst has resulted in the enlargement of specific surface area and increased defective sites, which improve the catalytic activity.