Electrochemical properties of intermediate-temperature SOFCs based on proton conducting Sm-doped BaCeO3 electrolyte thin film

Dense BaCe_0.8Sm_0.2O_2.90 (BCSO) thin films were successfully fabricated on porous NiO–BCSO substrates by dry pressing process. As characterized by scanning electron microscope, the BCSO films were about 50 μm. With Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCF) as cathodes, single cells were tested at 600 and 700 °C with humidified (3% HB₂O) hydrogen as fuel and oxygen as oxidant. The open circuit voltage of 1.049 V at 600 °C and 1.032 V at 700 °C were achieved, indicating negligible gas permeation through the BCSO thin films. Maximum power densities of 132 and 340 mW/cm² were obtained at 600 and 700 °C, respectively. The impedance measurements at open circuit conditions showed that there were two rate-limiting processes for the electrode reactions and that the cell performances were essentially determined by the electrode polarization resistances at temperature below 650 °C, which implied that it was essential to reduce the electrode polarization by developing novel electrode materials to improve the performance of ITSOFC based on BCSO electrolyte. Conductivities of BCSO under the cell operating circumstances were obtained as 0.00416, 0.00662 and 0.00938 Scm^− 1 at 500, 600 and 700 °C, respectively. The activation energy of BCSO conductivity was calculated as 29.5 and 43.8 kJ/mol for the temperature range of 550–700 °C and of 400–550 °C, respectively. Endurance test was firstly carried out with 75 μm BCSO electrolyte at 650 °C at the operating voltage of 0.7 V and current density about 0.12 A/cm². Both voltage and current density remained stable for 1000 min.