Bifunctional electrocatalytic activity of La_0.8Sr_0.2MnO₃-based perovskite with the A-site deficiency for oxygen reduction and evolution reactions in alkaline media

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 La_0.8Sr_0.2MnO₃-based perovskite by introducing the deficiency in the A-site and transition-metal Fe in the B-site. Bifunctional electrocatalysts La_0.8Sr_0.2MnO₃, (La_0.8Sr_0.2)_0.98MnO₃, (La_0.8Sr_0.2)_0.95MnO₃ and (La_0.8Sr_0.2)_0.95Mn_0.5Fe_0.5O₃ were prepared by a facile sol–gel process. The material characterization results showed that compared with La_0.8Sr_0.2MnO₃, (La_0.8Sr_0.2)_0.98MnO₃ and (La_0.8Sr_0.2)_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: La_0.8Sr_0.2MnO₃ < (La_0.8Sr_0.2)_0.98MnO₃ < (La_0.8Sr_0.2)_0.95MnO₃. With partial substitution of Mn by Fe in the B-site, the (La_0.8Sr_0.2)_0.95Mn_0.5Fe_0.5O₃ perovskite oxide exhibits even better electrocatalytic activity. Further experiments reveal that (La_0.8Sr_0.2)_0.95Mn_0.5Fe_0.5O₃ 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.