Gd and cu co-doped BaFeO3-δ as a cobalt-free air electrode for solid oxide electrolysis cell

Solid oxide electrolysis cell (SOEC) is an efficient and environmentally friendly energy conversion device. The commercialization of SOEC is limited by the oxygen electrodes, whose problems include high costs and unexpected degradation of cobalt/strontium. In this study, we proposed a co-doping strategy and synthesized cobalt-free and strontium-free perovskite materials, specifically Ba_0.95Gd_0.05Fe_1-xCu_xO_3-δ (BGFCu_x), via the sol-gel method. These materials were evaluated as potential air electrodes for SOEC. The BGFCu_x samples were systematically characterized by crystal structure, oxygen content, thermal properties, electrical conductivity, and electrochemical performance. X-ray diffraction results show that the solid-solution concentration of Cu in BGFCu_x cannot exceed 0.1. X-ray photoelectron spectroscopy results suggest that Cu doping increases oxygen vacancy concentration. Among all BGFCu_x perovskites, BGFCu0.1 exhibited a low polarization resistance of 0.069 Ω·cm² at 800 °C (0.2 V) and a high current density of 216 mA·cm⁻² at an anodic bias of 40 mV. Hence, the Gd and Cu co-doped BGFCu0.1 perovskite material is a promising air electrode for SOEC.