Electrochemical CO2 reduction to CO using solid oxide electrolysis cells with high-performance Ta-doped bismuth strontium ferrite air electrode

Electrochemical CO2 reduction to CO by using solid-oxide electrolysis cells (SOECs) is a promising option to produce useable fuels using renewable energy. However, traditional cobalt-based air electrodes exhibit high thermal-expansion coefficients and a tendency of Co segregation, compromising long-term stability. Here, Co-free Bi0.5Sr0.5FeO3-δ perovskite was explored with Ta doping into the B-site as the air electrode (BSFTx). Doping Ta enabled a decrease in polarization resistance by 45% from 0.31 Ω cm2 to 0.17 Ω cm2 at 700 °C. The distribution function of relaxation times analysis suggested that the observed improvements can be ascribed to the enhanced mass-transfer processes, which include oxygen diffusion, association, and desorption. The performance of a cathode-supported Ni-YSZ (ytttria-stabilized zirconia)|YSZ|Gd-doped ceria|BSFTx cell was characterized by an electrolysis current of −0.81 A cm−2 under 1.5 V at 800 °C, which corresponds to a CO-production rate of 4.2 × 103 nmol s−1 cm−2 and an electrical efficiency of 98%. Excellent stability of the cell was also demonstrated by steady current density during the 32-h test executed under 1.2 V at 800 °C. The nearly 100% electrical efficiency and the satisfactory performance and stability of SOEC with Ta-doped BSF air electrode indicated its potential use in CO2 reduction technique.