Double Perovskites as Model Bifunctional Catalysts toward Rational Design: The Correlation between Electrocatalytic Activity and Complex Spin Configuration

Abstract

The oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) properties of double perovskite catalysts La₂CoMnO_6-δ and La₂NiMnO_6-δ have been investigated. The experimental results demonstrate that these samples are efficient OER and ORR catalysts. For the La₂CoMnO₆ compound annealed at 600 °C, its half-wave potential of ORR in alkaline media is as low as 0.75 V versus reversible hydrogen electrode. As for the correlation between electrocatalytic activities and the e_g orbital occupation numbers, it is found that the e_g-filling rule proposed by Shao-Horn and co-workers is valid in La₂CoMnO_6-δ when the e_g electrons of two kinds of transition-metal ions are all considered. In the case of La₂NiMnO_6-δ, because the samples which prepared in different conditions all have unity average e_g occupation, the e_g-filling rule should be amended. We suggest that the average deviation from unity e_g occupation is a suitable activity descriptor, which can be used to design perovskite catalysts with unity average e_g occupation.