Correlation between Calcination Temperature and Bifunctional Catalytic Activity for Oxygen Electrode Reactions of Pyrochlore-type Metal Oxide Containing Bi and Ru

We investigated the oxygen electrode reactions (oxygen reduction reaction (ORR) and oxygen evolution reaction (OER)) of a pyrochlore-type metal oxide containing Bi and Ru (BRO), for aqueous air batteries. Here, we report the correlation between the calcination temperature of BRO and its catalytic activity in a KOH aqueous solution. It was found that the number of oxygen vacancies of BRO increased and the Tafel slopes for the ORR and OER decreased with an increase in the calcination temperature. The results of this study suggest that the oxygen vacancies of BRO are one of the factors that determine the catalytic activity for not only the ORR but also the OER.