Synergistic effect of B site co-doping with Co and Ce in bifunctional oxygen electrocatalysis by oxygen deficient brownmillerite Ba2In2O5

Abstract

Specificity in oxygen reduction and evolution reactions is pivotal in bifunctional catalysts in advanced energy devices which are expected to be active in a wide potential window and stable in both electrochemically reducing and oxidising atmospheres. State of the art noble metal catalysts for these reactions are fraught with issues whereas, metal oxides are expected to be stable in large potential window and can be tuned to have better bifunctional activity. Catalytically active metals, redox centres, oxygen vacancies etc. are some of the features of structured oxides which can be exploited in oxygen electrocatalysis. Brownmillerite family of compounds with general formula, A2B2O5 has high concentrations of ordered oxygen vacancy in a layer and can be promising bifunctional oxygen electrocatalysts, by appropriate B site doping. Ba2In2O5 is a well-studied system for its oxide ion conductivity and proximity of active B sites to O vacancies provide good O adsorption sites which are catalytically active. Here, cobalt and cerium are co-doped in Ba2In2O5, anticipating a synergistic effect of Ce(III)/Ce(IV) redox centre in ORR and Co activity in OER along with O vacancies providing adsorption sites. We have studied the structural changes associated with the doping by Rietveld refinement of the XRD patterns and correlated the structure to bifunctional oxygen electrocatalytic activity which is found to enhance on increasing the Co and Ce content.