Iron-Based Perovskites for Catalyzing Oxygen Evolution Reaction

The slow kinetics of the oxygen evolution reaction (OER) is the main cause of energy loss in many low-temperature energy storage techniques, such as metal-air batteries and water splitting. A better understanding of both the OER mechanism and the degradation mechanism on different transition metal (TM) oxides is critical for the development of the next generation of oxides as OER catalysts. In this paper, we systematically investigated the catalytic mechanism and lifetime of ABO_3-δ perovskite catalysts for the OER, where A = Sr or Ca and B = Fe or Co. During the OER process, the Fe-based AFeO_3-δ oxides with δ ≈ 0.5 demonstrate no activation of lattice oxygen or pH dependence of the OER activity, which is different from the SrCoO_2.5 with similar oxygen 2p-band position relative to the Fermi level. The difference was attributed to the larger changes in the electronic structure during the transition from the oxygen-deficient brownmillerite structure to the fully oxidized perovskite structure and the poor conductivity in Fe-based oxides, which hinders the uptake of oxygen from the electrolyte to the lattice under oxidative potentials. The low stability of Fe-based perovskites under OER conditions in a basic electrolyte also contributes to the different OER mechanism compared with the Co-based perovskites. This work reveals the influence of TM composition and electronic structure on the catalytic mechanism and operational stability of the perovskite OER catalysts.