Nickel-doped BaCo_0.4Fe_0.4Zr_0.1Y_0.1O_3-δ as a new high-performance cathode for both oxygen-ion and proton conducting fuel cells

To develop a cathode with excellent oxygen reduction reaction (ORR) activity and durability at intermediate-to-low temperatures is significant to boost the advancement of solid oxide fuel cells (SOFCs), a fascinating energy conversion technology with low emissions and high efficiency. Perovskite oxides have been extensively developed as cathodes, and doping is an important strategy to alter the lattice diffusion and surface exchange properties of perovskites, to tailor catalytic performances for various redox reactions, including ORR for SOFCs. The reported BaCo_0.4Fe_0.4Zr_0.1Y_0.1O_3-δ (BCFZY) is a promising cathode for SOFCs. Herein, to further improve the performance of BCFZY at reduced temperatures, we systematically investigate the partial doping of B-sites with different metal elements, including Mn, Ni, Cu and Zn at a fixed content of 5%. Among them, it is found that Ba(Co_0.4Fe_0.4Zr_0.1Y_0.1)_0.95Ni_0.05O_3-δ (BCFZYN) exhibits the lowest polarization impedance in both oxygen ion and proton conducting fuel cells. Based on conductivity relaxation experiments and oxygen and hydrogen permeation tests, it is found that nickel doping improves oxygen mobility, surface exchange kinetics, and bulk oxygen ion and proton conductivity. Thereby, a high ORR activity on oxygen ion and proton conducting electrolytes is achieved, reaching 0.038 and 0.607 Ω cm² at 550 °C, respectively. The cells with the BCFZYN electrode show outstanding operational stability (200 h of operation in a symmetrical cell and 1000 h of operation in a single cell). This suggests that the BCFZYN is a promising cathode of next-generation SOFCs.