Comparison of the oxygen reduction mechanisms in a GBCO–SDC-impregnated cathode and a GBCO cathode

Abstract

In this paper, a GdBaCo2O5+δ–Ce0.8Sm0.2O1.9 (GBCO–SDC) composite cathode was prepared by the impregnation method with GdBaCo2O5+δ (GBCO) as the impregnating phase and Ce0.8Sm0.2O1.9 (SDC) as the cathode skeleton. X-ray diffraction (XRD) analysis showed a good chemical compatibility between GBCO and SDC, and there were no obvious impurities at high temperature. The particle size of GBCO was approximately 80 nm. The continuous GBCO phase was deposited on the surface of porous SDC backbones, which greatly improved the electrochemical activity of the cathode. The polarization resistance of GBCO–SDC-impregnated cathode was 0.50 Ω cm2 at 600 °C, which was only ~ 28.6% of that of pure GBCO cathode. The oxygen reduction reaction (ORR) at GBCO cathode mainly involved the adsorption–dissociation of oxygen molecules and charge-transfer process of oxygen atoms. The two ORR rate-controlling steps were the adsorption–dissociation process at 500–600 °C and the charge-transfer processes at 600–700 °C, respectively. The oxygen reduction reaction at GBCO–SDC-impregnated cathode mainly involved the diffusion of oxygen ions through the three phase boundaries and the charge transfer of oxygen atoms, in which the charge-transfer process was always the ORR rate-controlling step.