Various volume fractions of perovskite-type Bi0.5Sr0.5FeO3-delta (BSF55) and double perovskite PrBaCo2O5+delta (PBCO) composite cathodes were prepared. The chemical compatibility of BSF55-PBCO composite material was confirmed by the absence of a secondary phase after firing below 850 degrees C for 2 h and annealing below 700 degrees C for 100 h. The electrode resistance of composite cathodes is indicated by Nyquist plots, all consisting of one arc in the high frequency (HF) range and another in the low frequency (LF) range. At 450 and 500 degrees C, the resistance in the HF range decreased linearly as the PBCO fraction increased, while BP73 showed the smallest arcs in the LF range. The activation energy of electrode resistance clearly decreased with the addition of up to 30 vol.% PBCO. This implies the mechanism of the oxygen reduction reaction underwent some changes due to the added PBCO. Considering the activation energy of the electrode resistance and the P(O-2) dependence of resistance at 700 degrees C, the addition of PBCO to BSF55 was shown to affect not only the mechanism but also the rate-determining step of oxygen reduction. (C) 2014 Elsevier BY. All rights reserved.