Properties of novel K-doped YBaCo4O7+δ cathode materials for proton conductor solid oxide fuel cells

To assess the potential of YBaCo 4 O 7+δ as a cathode material for proton-conducting solid oxide fuel cells (SOFCs), a proton-oxygen-ion-electron three-phase conductive cathode, YBa 1- x K x Co 4 O 7+δ , was synthesized via the sol-gel method and analyzed concerning its crystal structure, thermal expansion behavior, and electrochemical properties. The results indicate that K doping increases the oxygen vacancy content and enhances proton conductivity. The polarization impedance reaches its minimum when x  = 0.05. K doping has a negligible impact on the coefficient of thermal expansion (CTE), and all doped samples exhibit CTEs that align well with common electrolyte materials, thus minimizing thermal stress during SOFC operation. Compared to YBaCo 4 O 7+δ , partial K doping improves the catalytic activity for the oxygen reduction reaction. An anode-supported single cell with the YBa 0.95 K 0.05 Co 4 O 7+δ cathode, using H 2 fuel, delivers a peak power density of 567 mW cm −2 at 700 °C, surpassing the performance of the YBaCo 4 O 7+δ cathode, which achieves 482 mW cm −2 under the same conditions. This study contributes to the development of hexagonal unit-cell cathodes with proton-oxygen-ion-electron three-phase conductivity and high catalytic activity for proton-conducting SOFCs.