Electrochemical oxygen reduction on layered mixed metal oxides: Effect of B-site substitution

Abstract

Oxygen reduction reaction (ORR) is critical in advancing the frontiers of electrochemical energy conversion and storage technologies. To date, Pt-based electrocatalysts exhibit state-of-the-art performance for low temperature ORR, but are hindered by their high cost. Therefore, it is imperative to find cost-effective alternatives for the practical realization of these technologies. Herein, we investigate the effect of layered, mixed metal oxides belonging to first-series Ruddlesden-Popper (R-P) phases with a general composition of A2BO4 (A=rare earth/alkaline earth metals; B=3d transition metal) for ORR in alkaline enviroment of anion exchange membrane fuel cells. We show that the nature of the B-site 3d transition metal in these oxides is critical in tuning the ORR activity. Using a combination of well-controlled synthesis, chemical, as well as electrochemical studies, we find that substitution of the Ni B-site in these oxides with nominal amounts of Mn and Co (La2Ni0.88Mn0.12O4 and La2Ni0.88Co0.12O4, respectively) leads to enhanced overall ORR activity by selective promotion of the electrochemical reduction of hydrogen peroxide, an intermediate in the pseudo 4e− ORR path. The reported findings can be used in designing nonprecious metal-based oxide electrocatalysts for oxygen reduction in alkaline anion exchange memebrane fuel cells.