High-Performance Perovskite Bifunctional Electrocatalysts for Oxygen Reduction Reaction and Oxygen Evolution Reaction

Perovskite structured earth-abundant metal oxides are attractive candidates as bifunctional electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in alkaline electrolytes. Herein, we present a series of perovskite electrocatalysts (La0.65Sr0.3)zFeO3−δ with different A-site cation deficiencies through a simple and scalable solid-state synthesis method. Their electrocatalytic activities toward ORR and OER are studied by rotating disk electrode and rotating-ring disk electrode techniques in an alkaline electrolyte. Two obvious oxygen reduction potential regions are first reported in this work for these perovskites; the electron transfer number during ORR in the first oxygen reduction potential region is ∼2 and that in the second region is ∼4, indicating two different ORR mechanisms in these two potential regions. Among these perovskites, (La0.65Sr0.3)1.00FeO2.95 exhibits the highest electrocatalytic activity for ORR in the first ORR potential region with an onset potential of 0.72 V, a potential of 0.6 V at −1 mA cm–2, and a Tafel slope of 60.4 mV dec–1 in 0.1 M KOH. For OER in the alkaline electrolyte, (La0.65Sr0.3)0.89FeO2.9 with the highest A-site cation deficiency is proved to be the most active catalyst among these perovskites, which is mainly caused by its highest surface oxygen vacancy content. As a result, our work could provide guidance in the further development of easily prepared, scalable, and earth-abundant perovskite metal oxides.