Synthesis of bifunctional BaFe1−xCoxO3−y−δ(OH)y catalysts for the oxygen reduction reaction and oxygen evolution reaction

Abstract

Perovskite oxides with mixed ionic and electronic conductivities are very promising candidates for their application as energy materials related to fuel cell and metal air battery integration. In this article, we report on the systematic characterization of mixed proton and electron conducting compounds of composition BaFe_1−xCo_xO_3−y−δ(OH)_y synthesized via nebulized spray pyrolysis. Independent of the value of x, all samples BaFe_1−xCo_xO_3−y−δ(OH)_y were found to crystallize in an orthorhombic ordering/distortion variant of the perovskite type structure (space group Cmcm) and are isotypic to the border phases (x = 0 or 1) reported previously. A minimum water content was observed for the composition with x = 0.5, which increases steadily for Co or Fe richer compositions. Impedance studies show that the conductivity increases with increasing Co-content, with BaCo_0.5Fe_0.5O_2.07(OH)_0.74 showing a total electrical conductivity of 10⁻⁷ S cm⁻¹ at 298 K, an order of magnitude higher than found for BaFeO_2.33(OH)_0.33. Further, bifunctional catalytic activity for the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) was found for the compounds of the series as investigated in 0.1 M KOH, with BaFe_0.8Co_0.2O_3−y−δ(OH)_y possessing the best bifunctional performance parameter of ΔU = 1.10 V, which is comparable to that of other non-precious metal catalysts.