Effect of Fe doping on PrBaCo2O5+δ as cathode for intermediate-temperature solid oxide fuel cells

PrBaCo2FexO5 + delta (PBCFx, 0 <= x <= 2.0) is investigated as cathode materials for intermediate temperature solid oxide fuel cells. X-ray diffraction confirms that the material retains double perovskite structure and undergoes structural change from tetragonal to cubic as the Fe doping level reaches to x =0.4. High-temperature X-ray diffraction patterns reveal that all the structures of PBCFx (x = 0.0 -> 0.4) are thermodynamically stable upon heating to 900 degrees C. The increased doping of Fe deteriorates the electrical conductivity monotonically, with an exception of a big jump in the conductivity at x =0.4, due to the structural change. Thus, except for the low temperature region of 50-400 degrees C, PBCF0.4 possesses maximum values in the electrical conductivity at temperature range of 500-900 degrees C among all the Fe doping levels in PBCFx. PBCF0.4 used as cathode in the symmetrical cells of PBCFx/Ce0.8Sm0.2O2-gamma (SDC) exhibits the lowest cathode polarization resistance: 0.07 Omega cm(2) and 0.13 Omega cm(2) at 750 degrees C and 700 degrees C respectively. For anode-supported button cells of PBCFx[SDC]NiO + SDC, the highest power density is also observed for PBCF0.4 with a maximal power density of 446.4 and 346.3 mW cm(-2) at 700 and 650 degrees C, respectively. We conclude that Fe doping does not increase the conduction properties by itself but improves the electrochemical properties indirectly by changing the structure of PBCFx from tetragonal into cubic. (C) 2011 Published by Elsevier B.V.