Correlation Between Calcination Temperature and Bifunctional Catalytic Activity for Oxygen Electrode Reaction of Bismuth Ruthenate Pyrochlore in KOH Solution

The oxygen electrode reactions (oxygen reduction reaction (ORR) and oxygen evolution reaction (OER)) of the pyrochlore-type metal oxide containing Bi and Ru (BRO) were investigated. In this study, we report that the correlation between the calcination temperature and the bifunctional catalytic activity of BRO in a KOH aqueous solution. BRO was prepared by the co-precipitation method in aqueous medium using Bi(NO3)3, RuCl3, and NaOH and following the calcination at 500–700 °C. The characterization was carried out by synchrotron XRD and temperature-programmed reduction technique. It was found that the oxygen contents of BRO decreased with rising the calcination temperature. The catalytic behavior of BRO towards ORR and OER was evaluated by hydrodynamic voltammetry using a rotating disk electrode and a rotating ring-disk electrode technique. Tafel slopes for the ORR and OER decreased with an increase in the calcination temperature from 500 to 600 °C, while the onset potentials for both reactions were almost same. The results of this study suggest that the oxygen content of BRO is one of the factors that determine the catalytic activity for the oxygen electrode reactions.