Kinetics of Cathodic Oxygen Reduction on Lanthanum-based Perovskite-type Oxides

Abstract

The kinetics of the electrochemical O2 reduction on fifteen lanthanum-based perovskite-type oxides in alkaline solution were examined systematically by use of a rotating ring-disk electrode (RRDE, Fig. 1). The electrode activities of the majority of oxides (the disk currents) incerased with an increase in mixing ratio of respective oxides to carbon (Fig. 2). The number of electrons (n) associated with O2 reduction was 2.3~4.0 on oxide (80wt%)-carbon (20 wt%) electrodes, in contrast to 2.0 on the pure carbon electrode (Fig. 3). Furthermore, ten oxides exhibited relatively high activities for catalytic decomposition of H202 (Fig. 9). Therefore, it is considered that there are two pathways for O2 reduction on the oxides (Fig. 4), i. e., Various kinetic parameters for 02 reduction on all the oxides were obtained by analysis of the data on RRDE (Fig. 5~Fig. 8). On the basis of these parameters, the oxides were classified into the following three groups (Table 1): group I (LaCrO3 and LaFeO3) having little activities for 4-electron O2 reduction (i) and HO2- decomposition (iii); groupIII(such as LaMnO3) having high activity only for reaction (i); group]III (most of oxides such as LaNiO3) having high activities for reactions (i) and (iii). The oxides in group II and III were excellent electrode catalysts: especially La0.6Sr0.4MnO3 in group III and La0.6Sr0.4Fe0.6 CO0.4O2 in group JH (Table 1). © 1985, The Chemical Society of Japan. All rights reserved.