Bismuth and niobium co-doped barium cobalt oxide as a promising cathode material for intermediate temperature solid oxide fuel cells

Abstract Perovskite oxides BaBi_0.05Co_0.95-yNb_yO_3-δ (BBCNy, 0 ≤ y ≤ 0.2) are synthesized and evaluated as potential cathode materials for intermediate temperature solid oxide fuel cells (IT-SOFCs). Highly charged Nb⁵⁺ successfully stabilizes the cubic perovskite structure to room temperature with Nb substituting content y ≥ 0.1. The phase structure, thermal expansion behavior, electrical conductivity and electrochemical performance of BBCNy with cubic phase are systematically studied. The samples exhibit excellent chemical compatibility with GDC and have sufficiently high electrical conductivities. However, the thermal expansion coefficients of BBCNy samples are nearly twice those of the most commonly used electrolyte materials YSZ and GDC, which is a major drawback for application in IT-SOFCs. The polarization resistances of BBCNy with y = 0.10, 0.15 and 0.20 on GDC electrolyte are 0.086, 0.079 and 0.107 Ω cm² at 700 °C, respectively. Even though the YSZ electrolyte membrane and GDC barrier layer are approximately 50 μm and 10 μm in thickness, the highest maximum power density (1.23 W cm^-2) of the single cell Ni-YSZ|YSZ|GDC|BBCN_0.15 is obtained at 750 °C. Good long-term stability of the single cell with BBCN_0.15 cathode is also demonstrated. These results demonstrate that BBCNy perovskite oxides with cubic structure are very promising cathode materials for IT-SOFCs.