Alkaline-earth elements (Ca, Sr and Ba) doped LaFeO3-δ cathodes for CO2 electroreduction

Abstract Alkaline-earth elements (Ca, Sr and Ba) doped LaFeO3-δ-based perovskite oxides are systematically studied to understand how these alkaline-earth elements influence the performance of the parent LaFeO3-δ for CO2 electroreduction. Their crystalline structure, phase stability, sintering property, oxygen desorption, CO2 adsorption, oxygen vacancies and the electron density of Fe cations are studied. Their electrochemical performance for CO2 reduction is evaluated at 800 °C. Distribution of relaxation time analysis of the impedance spectra is conducted to deeply investigate the electrochemical processes occurring on these perovskite cathodes. Our results show that alkaline-earth elements doping improves oxygen desorption and CO2 adsorption ability without phase structure changes. Meanwhile, the oxygen vacancies and the electrons density of Fe under electroreduction conditions are increased by doping alkaline-earth elements. These changes promote the electrochemical processes of CO2 electroreduction. Ca doping leads to performance decaying quickly under high voltages, while Ba doping increases the interface resistance due to the formation of carbonates. Sr is the best choice among the three alkaline-earth elements. The optimal doping amount of Sr is 20% in the La-site. Excessive Sr doping results in the formation of carbonates on the surface, thus hindering the charge transfer and decreasing the number of active sites.