Characteristics of Cu and Mo-doped Ca3Co4O9− cathode materials for use in solid oxide fuel cells

Abstract In this study, Cu and Mo ions were doped in Ca 3 Co 4 O 9− δ to improve the electrical conductivity and electrochemical behavior of Ca 3 Co 4 O 9− δ ceramic and the performance of a solid oxide fuel cell (SOFC) single cell based on NiO-SDC/SDC/doped Ca 3 Co 4 O 9− δ -SDC were examined. Cu substitution in the monoclinic Ca 3 Co 4 O 9− δ ceramic effectively enhanced the densification, slightly increased the grain size, and triggered the formation of some Ca 3 Co 2 O 6 ; however, no second phase was found in porous Mo-doped Ca 3 Co 4 O 9− δ ceramics even when the sintering temperature reached 1050 °C. Substitution of Cu ions caused slight increase in the Co 3+ and Co 4+ contents and decrease in the Co 2+ content; however, doping with Mo ions showed the opposite trend. Doping the Ca 3 Co 4 O 9− δ ceramic with a small amount of Cu or Mo increased its electrical conductivity. The maximum electrical conductivity measured was 218.8 S cm −1 for the Ca 3 Co 3.9 Cu 0.1 O 9− δ ceramic at 800 °C. The Ca 3 Co 3.9 Cu 0.1 O 9− δ ceramic with a coefficient of thermal expansion coefficient of 12.1×10 −6 K −1 was chosen as the cathode to build SOFC single cells consisting of a 20 μm SDC electrolyte layer. Without optimizing the microstructure of the cathode or hermetically sealing the cell against the gas, a power density of 0.367 Wcm −2 at 750 °C was achieved, demonstrating that Cu-doped Ca 3 Co 4 O 9− δ can be used as a potential cathode material for IT-SOFCs.