LNF SOFC cathodes with active layer using Pr6O11 or Pr-doped CeO2

Abstract We fabricated electrolyte supported single cells with three types of cathodes that consisted of a Ce0.1Gd0.1O1.95 (GDC) buffer layer, a LaNi0.6Fe0.4O3 (LNF) cathode and an active layer. The only difference between the three cathodes was that each had a different active layer, namely a GDC–LNF composite active layer (our conventional cathode), a PrxCe1–xO2–δ (x = 0.1, 0.3, 1.0)–LNF composite active layer and a Pr6O11 (PrxCe1–xO2–δ (x = 1.0)) active layer. The interface resistance, Rinf, and overvoltage, ηc, of the cathodes were investigated. At 800 °C, the Rinf of the cathode with the Pr6O11 active layer was reduced to 1/30 that of the cathode with the GDC–LNF composite active layer. The Rinf at 800 °C for the cathode with the Pr6O11–LNF composite active layer was reduced to 1/8 that of the cathode with the GDC–LNF composite active layer. The Rinf values of the cathode with an active layer between 650 and 750 °C were also much better than those of the cathode with the GDC–LNF composite active layer. By using the cathode with the Pr6O11 active layer, the operating temperature can be reduced to 700 °C while retaining the same performance (same overvoltage at 254 mA/cm2) as a cathode with a GDC–LNF composite active layer at 800 °C. We also investigated the reactions at the interfaces in the sintering process. X-ray diffraction (XRD) analysis revealed that the Pr6O11 reacted easily with zirconia, and Pr2Zr2O7 was produced at 1000 °C or above. It was suggested that the sintering temperature of the cathodes with the active layer could be increased to around 1000 °C without any reaction at the interface between Pr6O11 and other materials.