Effect of Cu doping on YBaCo2O5+δ as cathode for intermediate-temperature solid oxide fuel cells

Abstract

Layered-perovskites YBaCo2-xCuxO5+δ (YBCCO, x=0.0, 0.2, 0.4, 0.6, 0.8) are synthesized by the sol-gel method and are assessed as potential cathode materials for utilization in intermediate-temperature solid oxide fuel cells (IT-SOFCs) on the La0.9Sr0.1Ga0.8Mg0.2O3-δ (LSGM) electrolyte. With increasing x from 0.0 to 0.8, the structure does not change but the lattice parameters and unit-cell volumes increase. From X-ray photoelectron spectra, it can be seen that both Cu and Co exist in a mixed oxidation state. Cu ions are prone to low oxidation state (Cu+ and Cu2+), while Co ions basically exhibit high oxidation state (Co3+ and Co4+). The conductivity of the YBCCO samples decreases with increasing Cu content, and the maximum conductivity of YBCCO is 143 S cm−1 at 300°C for the x=0.0 sample. The thermal expansion coefficient of samples significantly decreases from 17.8×10−6K−1 for x=0.0 to 13.4×10−6K−1 for x=0.8 in the temperature range of 30–850°C. With increasing Cu substitution content for Co, the electrode polarization resistance (Rp) increases. The Rp values of the YBCCO (x =0.6) cathode on the LSGM electrolyte are 0.125Ω cm2 and 0.076Ω cm2 at 700°C and 750°C, respectively. The maximum power densities of the single cells fabricated with the LSGM electrolyte, Ce0.8Gd0.2O1.9 (GDC) interlayer, NiO/GDC anode and YBCCO (x=0.6) cathode reach 815, 642 and 479 mW cm−2 at 850, 800 and 750°C, respectively. This study suggests that the layered-perovskites YBCCO can be potential candidates for utilization as IT-SOFC cathodes.