Enhanced mechanisms of oxygen reduction on Pr0.4Sr0.6Co0.2Fe0.8O3-δ impregnated La1−xSrxCo1−yFeyO3-δ cathodes for solid oxide fuel cells

Surface modification is an effective approach for the improvement of the electrochemical performance of cathodes. Here effects of perovskite-structured Pr0.4Sr0.6Co0.2Fe0.8O3-δ (PSCF) modification are investigated on the electrochemical performance of La1−xSrxCo1−yFeyO3-δ (LSCF) cathodes with experimental and theoretical methods. The formation energies of oxygen vacancy are reduced with PSCF modification and the adsorption energies of oxygen adsorption on PSCF modified LSCF surface are lower than those on the LSCF surface. Also the dissociation barriers of oxygen molecules on the LSCF surface are greatly decreased, indicating that the rate of oxygen reduction reaction is greatly improved and the LSCF surface is activated with PSCF modification. Results of electrochemical impedance spectra tests show that polarization resistance (Rp) of LSCF cathodes decreases with the appropriate amount of PSCF impregnation and reaches the lowest Rp (0.055 Ω cm2) with about 10 wt% impregnation at 750 °C. Results of electrical conductivity relaxation indicate that the performance improvement of LSCF cathodes mainly results from the increase of oxygen surface exchange property (5.4 ×10−4 and 1.1 ×10−3 cm s−1), which is consistent with the calculation results.