Composition-Dependent Reactivity of Ba0.5Sr0.5Co x Fe1? x O3?? toward the Oxygen Reduction Reaction

The electrochemical activity toward the oxygen reduction reaction (ORR) of carbon supported Ba0.5Sr0.5CoxFe1?xO3?? electrode particles is studied for the first time as a function of chemical composition (1 < x < 0). Highly crystalline Ba0.5Sr0.5CoxFe1?xO3?? particles with the full compositional range were synthesized by an ionic-liquid route, leading to a high degree of phase purity. The structure and composition of the materials were investigated by quantitative XRD and EDX. Electrochemical studies in oxygen-saturated alkaline solutions show that the overall reactivity of the catalyst supported on mesoporous carbon increases as the Co content increases above 50%. DFT calculations, based on the structural parameters obtained from XRD refinements, show that the oxygen-vacancy formation energy decreases as the Co content increases. Oxygen vacancies lead to a higher electron density at the Co atoms, which are identified as the key ORR active sites.