Cobalt-Doped BaInO Brownmillerites: An Efficient Electrocatalyst for Oxygen Reduction in Alkaline Medium.

A series of compounds with cobalt doping in the indium site of BaInO brownmillerites exhibited excellent oxygen reduction activity under alkaline conditions. Doping (25%) retains the brownmillerite structure with disorder in the O3 site in the two-dimensional alternate layer along the plane. Further substitution of cobalt in the indium site leads to the loss of a brownmillerite structure, and the compound attains a perovskite structure. Cobalt-doped samples exhibited far better oxygen reduction reaction (ORR) activity when compared to the parent BaInO brownmillerite. Among the series of compounds, BaInCoO with the highest Co doping and oxygen vacancies randomly distributed in the lattice exhibited the best ORR activity. BaInCoO showed a 40 mV positive shift in the onset potential with better limiting current density and a nearly four-electron-transfer reduction pathway when compared to the parent BaInO brownmillerite.