Tailoring electrochemical property of layered perovskite cathode by Cu-doping for proton-conducting IT-SOFCs

Layered perovskite oxide YBaCuCoO_5+x (YBCC) was synthesized by an EDTA-citrate complexation process and was investigated as a novel cathode for proton-conducting intermediate temperature solid oxide fuel cells (IT-SOFCs). The thermal expansion coefficient (TEC) of YBCC was 15.3×10^-6K^-1 and the electrical conductivity presented a semiconductor-like behavior with the maximum value of 93.03 Scm^-1 at 800°C. Based on the defect chemistry analysis, the electrical conductivity gradually decreases by the introduction of Cu into Co sites of YBaCo₂O_5+x and the conductor mechanism can transform from the metallic-like behavior to the semiconductor-like behavior. Thin proton-conducting (BaZr_0.1Ce_0.7Y_0.1Yb_0.1O_3-δ) BZCYYb electrolyte and NiO-BZCYYb anode functional layer were prepared over porous anode substrates composed of NiO-BZCYYb by a one-step dry-pressing/co-firing process. Laboratory-sized quad-layer cells of NiO-BZCYYb / NiO-BZCYYb / BZCYYb / YBCC with a 20 μm-thick BZCYYb electrolyte membrane exhibited the maximum power density as high as 435 mWcm^-2 with an open-circuit potential (OCV) of 0.99V and a low interfacial polarization resistance of 0.151 Ωcm² at 700°C. The experimental results have indicated that the layered perovskite oxide YBCC can be a cathode candidate for utilization as proton-conducting IT-SOFCs.