Oxygen Reduction Reaction Over (Ba,Sr)(6)Re2co4o15-Ba(Ce,Pr,Y)O-3 Composite Cathodes For Proton-Conducting Ceramic Fuel Cells

In this study, the effect of elemental substitution, especially the Ba/Sr ratio and rare-earth elements, in (Ba,Sr)(6)RE2Co4O15 (RE = La, Pr, Nd, Sm, Gd) and the composite effect with BaCe0.5Pr0.3Y0.2O3-delta on the activity for the oxygen reduction reaction were studied to develop high-performance cathodes for proton-conducting ceramic fuel cells. The polarization resistance of (Ba6-xSrx)RE2Co4O15 electrodes decreased with an increase in the Ba/Sr ratio, while the activity did not change systematically along the periodic table when the rare-earth element was substituted. Although the polarization resistance of Ba5SrGd2Co4O15 was about one order of magnitude lower than that of Ba4Sr2Sm2Co4O15 at 500 degrees C, the composite of Ba5SrGd2Co4O15-BaCe0.5Pr0.3Y0.2O3-delta (30 : 70 wt%) exhibited comparable performance and activation energy to Ba4Sr2Sm2Co4O15-BaCe0.5Pr0.3Y0.2O3-delta (30 : 70 wt%): polarization resistance - 0.20 omega cm(2) and 0.52 omega cm(2) at 600 degrees C and 500 degrees C, respectively, and activation energy - 61.8 kJ mol(-1). Then, the reason for the high performance of the Ba5SrGd2Co4O15-BaCe0.5Pr0.3Y0.2O3-delta (30 : 70 wt%) composite was studied in detail, especially from the viewpoint of elemental interdiffusion. Finally, the plausible oxygen reduction reaction mechanism on this composite was proposed.