High-Performance\nPerovskite Bifunctional Electrocatalysts\nfor Oxygen Reduction Reaction and Oxygen Evolution Reaction

Abstract

Perovskite\nstructured earth-abundant metal oxides are attractive\ncandidates as bifunctional electrocatalysts for oxygen reduction reaction\n(ORR) and oxygen evolution reaction (OER) in alkaline electrolytes.\nHerein, we present a series of perovskite electrocatalysts (La_0.65Sr_0.3)_<i>z</i>FeO_3−δ with different A-site cation deficiencies through a simple and scalable\nsolid-state synthesis method. Their electrocatalytic activities toward\nORR and OER are studied by rotating disk electrode and rotating-ring\ndisk electrode techniques in an alkaline electrolyte. Two obvious\noxygen reduction potential regions are first reported in this work\nfor these perovskites; the electron transfer number during ORR in\nthe first oxygen reduction potential region is ∼2 and that\nin the second region is ∼4, indicating two different ORR mechanisms\nin these two potential regions. Among these perovskites, (La_0.65Sr_0.3)_1.00FeO_2.95 exhibits the highest\nelectrocatalytic activity for ORR in the first ORR potential region\nwith an onset potential of 0.72 V, a potential of 0.6 V at −1\nmA cm^–2, and a Tafel slope of 60.4 mV dec^–1 in 0.1 M KOH. For OER in the alkaline electrolyte, (La_0.65Sr_0.3)_0.89FeO_2.9 with the highest\nA-site cation deficiency is proved to be the most active catalyst\namong these perovskites, which is mainly caused by its highest surface\noxygen vacancy content. As a result, our work could provide guidance\nin the further development of easily prepared, scalable, and earth-abundant\nperovskite metal oxides.