Nb-doped PrBa_0.8Ca_0.2Co₂O₆-based perovskite cathode with improved oxygen reduction reaction activity and stability for solid oxide fuel cells

The performance of a solid oxide fuel cell (SOFC) is strongly associated with the activity and durability of the cathode, where the oxygen reduction reaction occurs. In this study, we report our findings in the development of an Nb-doped PrBa_0.8Ca_0.2Co₂O_6−δ (PrBa_0.8Ca_0.2Co_2−xNb_xO_6−δ, x = 0, 0.025, 0.05, and 0.1, denoted as PBCCN_x) perovskite composite as the SOFC cathode. Analyses of X-ray diffraction (XRD) patterns and energy-dispersive transmission electron microscopy (TEM-EDS) images suggest that after being treated at 950 °C in air, PBCCN_0.05 mainly contains phases of Ca- and Nb-doped PrBaCo₂O_6−δ double perovskite, PrCoO₃ perovskite with Ca and Nb doping, and Ba₃Ca_1.18Nb_1.82O_9−δ. When evaluated as an SOFC cathode, the PBCCN_0.05 mixture has shown a low polarization resistance of 0.0074 Ω∙cm² at 800 °C in La_0.8Sr_0.2Ga_0.8Mg_0.2O₃ electrolyte symmetrical cells. Accordingly, anode-supported single cells with a configuration of Ni–Zr_0.84Y_0.16O_2−δ (YSZ)/YSZ/Gd_0.1Ce_0.9O_2−δ/PBCCN_0.05 display high electrochemical performance, with a peak power density of 1.81 W∙cm⁻² and a reasonable durability of 100 h at 800 °C. PBCCN_0.05 possesses a higher concentration of oxygen vacancies, a faster oxygen surface adsorption‒dissociation rate, and an increased mass ratio of PrCoO₃ perovskite with Ca and Nb doping compared to PrBa_0.8Ca_0.2Co₂O_6−δ without Nb doping.