Hydrothermal preparation and electrochemical properties of Gd3+ and Bi3+, Sm3+, La3+, and Nd3+ codoped ceria-based electrolytes for intermediate temperature-solid oxide fuel cell

The structure, the thermal expansion coefficient, electrical conductivities of Ce0.8Gd0.2−xMxO2−δ (for M: Bi, x = 0–0.1, and for M: Sm, La, and Nd, x = 0.02) solid solutions, prepared for the first time hydrothermally, are investigated. The uniformly small particle size (28–59 nm) of the materials allows sintering of the samples into highly dense ceramic pellets at 1300–1400 °C. The maximum conductivity, σ700 °C around 4.46 × 10−2 S cm−1 with Ea = 0.52 eV, is found at x = 0.1 for Bi-co-doping. Among various metal-co-dopings, for x = 0.02, the maximum conductivity, σ700 °C around 2.88 × 10−2 S cm−1 with Ea = 0.67 eV, is found for Sm-co-doping. The electrolytic domain boundary (EDB) of Ce0.8Gd0.1Bi0.1O2−δ is found to be 1.2 × 10−19 atm, which is relatively lower than that of the singly doped samples. The thermal expansion coefficients, determined from high-temperature X-ray data are 11.6 × 10−6 K−1 for the CeO2, 12.1 × 10−6 K−1 for Ce0.8Gd0.2O2−δ, and increase with co-doping to 14.2 × 10−6 K−1 for Ce0.8Gd0.18Bi0.02O2−δ. The maximum power densities for the single cell based on the codoped samples are higher than that of the singly doped sample. These results suggest that co-doping can further improve the electrical performance of ceria-based electrolytes.