Valence electronic structure on oxygen reduction reaction kinetics of Cu-doped Ba0.5Sr0.5FeO3_ δ for IT-SOFCs

Ba0.5Sr0.5Fe1-xCuxO3-delta (BSFCx, x = 0-0.2) cathodes were investigated in the relationship between electronic structure and oxygen reduction reaction (ORR) kinetics. Electronic structure analysis revealed that Cu doping increased the oxygen vacancies (delta) from 0.384 (BSF) to 0.638 (BSFC0.2). The valence band maximum (VBM) shifted from 0.68 eV (BSF) to 0.24 eV (BSFC0.2), which implies a lower activation energy for charge transfer to the adsorbed oxygen. The area specific resistance was 0.042 Omega cm2 at 700 degrees C (BSFC0.2), a reduction of more than 50 % compared to 0.086 Omega cm2 (BSF). For the distribution of relaxation times analysis, BSFC0.2 showed the smallest peak area in medium frequency region, where the charge exchange and ion transfer occur at cathode.