Bifunctional electrocatalytic activity of La₀.₈Sr₀.₂MnO₃-based perovskite with the A-site deficiency for oxygen reduction and evolution reactions in alkaline media

Abstract

The development of efficient noble-metal free electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is of great importance for energy storage devices, such as fuel cell and zinc-air battery. In this work, we report a facile approach to enhance the electrocatalytic activity of La0.8Sr0.2MnO3-based perovskite by introducing the deficiency in the A-site and transition-metal Fe in the B-site. Bifunctional electrocatalysts La0.8Sr0.2MnO3, (La0.8Sr0.2)0.98MnO3, (La0.8Sr0.2)0.95MnO3 and (La0.8Sr0.2)0.95Mn0.5Fe0.5O3 were prepared by a facile sol–gel process. The material characterization results showed that compared with La0.8Sr0.2MnO3, (La0.8Sr0.2)0.98MnO3 and (La0.8Sr0.2)0.95MnO3 have smaller particle size, more oxygen vacancies and proper Mn valence, which will benefit both ORR and OER. The results were verified by testing the electrocatalytic activities using rotating-disk electrode (RDE) in alkaline media. For the perovskite oxides with only A-site cation deficiency, the bifunctional electrocatalytic activities increase in the following order: La0.8Sr0.2MnO3< (La0.8Sr0.2)0.98MnO3 < (La0.8Sr0.2)0.95MnO3. With partial substitution of Mn by Fe in the B-site, the (La0.8Sr0.2)0.95Mn0.5Fe0.5O3 perovskite oxide exhibits even better electrocatalytic activity. Further experiments reveal that (La0.8Sr0.2)0.95Mn0.5Fe0.5O3 has the highest current density (4.5 mA cm−2) in ORR which is comparable to commercial Pt/C (5 mA cm−2) and the enhancement of the OER is more obvious than that of the ORR. Subsequently, the perovskite samples were used as the cathode catalysts in zinc-air batteries. The results further prove that proper use of A-site deficiency and B-site Fe doping in perovskite oxides can boost up the electrocatalytic activities.