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The electrochemical performance and structural features of (La 1Ày Ca y )(Co x Fe 1Àx )O 3 cathode prepared via a citrate acid gel route are studied when it is interfaced with the (La 1.8 Dy 0.2 ) (Mo 2Àz W z )O 9 electrolyte. The resistance and chemical capacitance of a low-frequency arc are extracted from the impedance results to evaluate its catalytic activity in oxygen reduction reaction (ORR). (La 0.75 Ca 0.25 )(Co 0.8 Fe 0.2 )O 3 cathode exhibits the minimum area-specific resistance of 0.9 X cm 2 and maximum capacitance of 5.7 mF/cm 2 at 8001C among the compositions of x 5 0.1-0.9 and y 5 0.25. As the Co content increases, the decrease in resistance outweighs the increase in capacitance so that the product of resistance and capacitance (RC time constant) decreases. In contrast, when varying the Ca content of the A-site, the changes in resistance and the capacitance compensate each other; hence the RC time constant is virtually unchanged with respect to the calcium content. Thus, Co is a more influential element than Ca on the ORR catalytic activity. The pore structure study reveals a small amount of Mo diffuses from the electrolyte into the cathode, and its quantity is reduced when interfaced to an electrolyte of high W content.