Oxygen Reduction Reaction Mechanism on PrSrCo2-x Fe x O5+d (x=0, 1, 2) and Sm0.2Ce0.8O1.9 Composite Cathodes for Intermediate-Temperature Solid Oxide Fuel Cells

Perovskite-type mixed ionic and electronic conductors are finding applications in intermediate-temperature solid oxide fuel cells. Here, we study the effects of substituting Co with Fe on the crystal structure and electrical and electrochemical properties of PrSrCo2-xFexO5+d (PSCF, x = 0, 1, 2). The electrochemical performance of symmetrical half-cells of PrSrCo2-xFexO5+d and Sm0.2Ce0.8O1.9 composite cathodes with the Sm0.2Ce0.8O1.9 electrolyte was measured using electrochemical impedance spectroscopy at 600-750 degrees C. The oxygen reduction reaction (ORR) mechanism was analyzed as a function of temperature and oxygen partial pressure (pO(2)) using the distribution function of relaxation times (DFRT). The electrical conductivity measurements of the PSCF pellets were in the range of 100-1300 S cm(-1). The PSCF (x = 1) - Sm0.2Ce0.8O1.9 composite cathode yielded the lowest area specific resistance (ASR) value of 0.07 Omega cm(2) at 750 degrees C for ORR. DFRT and pO(2) studies showed that impedance arcs corresponding to the high frequency could be attributed to the oxygen ion transfer resistance while the medium-low frequency impedance arcs could be correlated with the charge transfer resistance at the cathode/gas interface followed by ion incorporation. This study demonstrates that the partial substitution of Fe on the Co site improves the ORR activity of PSCF perovskites.