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

PrBaCo2-xFexO5 + δ (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 °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 °C, PBCF0.4 possesses maximum values in the electrical conductivity at temperature range of 500–900 °C among all the Fe doping levels in PBCFx. PBCF0.4 used as cathode in the symmetrical cells of PBCFx/Ce0.8Sm0.2O2-γ (SDC) exhibits the lowest cathode polarization resistance: 0.07 Ω cm2 and 0.13 Ω cm2 at 750 °C and 700 °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 °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.

► PBCF0.4 shows the highest electrical conductivity between 500~900 °C.
► Rp values of PBCF0.4 are 0.07 Ω·cm2 and 0.13 Ω·cm2 at 750°C and 700 °C respectively.
► The maximal power densities for PBCF0.4- button cell are 446.4 mW·cm− 2 at 700 °C.