Bifunctional electrocatalytic activity of La0.8Sr0.2MnO3-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 0.8 Sr 0.2 MnO 3 -based perovskite by introducing the deficiency in the A-site and transition-metal Fe in the B-site. Bifunctional electrocatalysts La 0.8 Sr 0.2 MnO 3 , (La 0.8 Sr 0.2 ) 0.98 MnO 3 , (La 0.8 Sr 0.2 ) 0.95 MnO 3 and (La 0.8 Sr 0.2 ) 0.95 Mn 0.5 Fe 0.5 O 3 were prepared by a facile sol–gel process. The material characterization results showed that compared with La 0.8 Sr 0.2 MnO 3 , (La 0.8 Sr 0.2 ) 0.98 MnO 3 and (La 0.8 Sr 0.2 ) 0.95 MnO 3 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 0.8 Sr 0.2 MnO 3  < (La 0.8 Sr 0.2 ) 0.98 MnO 3  < (La 0.8 Sr 0.2 ) 0.95 MnO 3 . With partial substitution of Mn by Fe in the B-site, the (La 0.8 Sr 0.2 ) 0.95 Mn 0.5 Fe 0.5 O 3 perovskite oxide exhibits even better electrocatalytic activity. Further experiments reveal that (La 0.8 Sr 0.2 ) 0.95 Mn 0.5 Fe 0.5 O 3 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.