Characterization of Fe- and Mn-doped GDC for low-temperature processing of solid oxide fuel cells

摘要

This study reports the development of a low-temperature solid oxide fuel cell (SOFC) based on gadolinium-doped-ceria (Gd_(0.1)Ce_(0.9)O_(1.95), GDC) electrolyte and copper anode. Single cells were fabricated by sintering of all three SOFC components - electrolyte, copper-based anode and composite cathode - in a single step at low temperature (900 ℃). Low-temperature sintering was necessitated due to the low melting point of copper and was achieved by the addition of transition metal oxides (TMOs) (Fe and Mn) to the GDC electrolyte. The sinterability of TMO-doped GDC samples was evaluated over 900-1400℃. Key functional properties - density, mechanical strength and electrical conductivity - of the doped GDC were determined. Acceptable levels of density (>95% of theoretical) and mechanical strength were achieved for the samples sintered at 900 ℃. Scanning electron micrographs (SEMs) of the doped-GDC samples showed no open pores at the lowest sintering temperature of 900 ℃ The electrical conductivities of the doped-GDC samples sintered at 900 ℃ at a test temperature of 650 ℃ were determined to be 0.0067 S cm~(-1) and 0.0095 cm~(-1) for Fe- and Mn-doped samples, respectively, but lower than that of undoped-GDC sintered at 1100℃ (σ_(650℃) = 0.027 S cm~(-1)). Single cells were prepared by slurry painting of CuO-GDC anode on one side of TMO-doped GDC electrolyte and Gd_(0.1)Ce_(0.9)O_(1.95) (GDC)-La_(0.6)Sr_(0.4)Co_(0.2)Fe_(0.8)O_3 (LSCF) composite cathode on the other side of the electrolyte followed by co-sintering of all the three layers at 900 ℃. The performance of the single cells was evaluated over 650-700 ℃ using humidified hydrogen as fuel and air as oxidant.