Oxide Ion Conduction and Surface Exchange Reactions of Mixed Conductive La0.65Ca0.35FeO3-δ Based on Oxygen Permeation Study

La0.65Ca0.35FeO3-delta (LCF6535) displayed higher oxygen permeation flux (J(O2)) compared to La0.6Sr0.4Co0.2Fe0.8O3-delta (LSCF) and could potentially replace the typical cathodes employed in solid oxide fuel cells. However, the oxide ion conduction and surface exchange reaction of the LCF6535 have not been studied thus far. This study investigates the ion conductivity and surface exchange reaction of LCF6535 by simultaneous investigation of the oxygen permeation flux and oxygen chemical potential. The ion conductivity (sigma(i)) of LCF6535 was determined to be 0.29 S cm(-1) at 1000 degrees C, and this high sigma(i) is the key contributor to the high J(O2) of LCF6535. Furthermore, the J(O2) of LCF 6535 at 800 and 850 degrees C was found to be limited by surface exchange reaction on the low oxygen partial pressure (P-l) side. The rate-determining step for the surface exchange reaction was determined to be the charge transfer relating to O-2 molecule desorption, which results from the lower hole concentration on the P-l side under the reduction condition. The increase in hole concentration achieved on the P-1 side is a possible solution for improving the surface exchange reaction and oxygen permeability.