Insight into high electrochemical activity of reduced La_0·3Sr_0·7Fe_0·7Ti_0·3O₃ electrode for high temperature CO₂ electrolysis

Electrochemical reduction of CO₂ under the high temperature electrolysis condition with favored kinetics is a promising method to utilize and convert CO₂ to valuable chemicals and to reduce its environmental impact. In this work, the electrochemical performance of perovskite-type La_0·3Sr_0·7Fe_0·7Ti_0·3O₃ (LSFT) oxide was thoroughly investigated as a cathode for high temperature solid oxide electrochemical reduction under practical CO₂ electrolysis conditions of various current densities, partial pressures, and different CO–CO₂ mixtures. The rate-limiting step of CO₂ reduction on the LSFT surface was determined by the electrochemical impedance spectroscopy technique with a three-electrode configuration. The exceptional performance of LSFT cathode is confirmed as reflected by the low polarization resistance and the extremely low activation energy. Moreover, improved electrode performance is also obtained on the reduced LSFT sample under reducing atmosphere with CO, while the rate-determining step is not changed. It is also confirmed that the reduced LSFT cathode gives increased surface oxygen vacancy concentration which is believed to serve as accommodation for chemical adsorption and consequently the active sites for electrochemical activation of CO₂, leading to the improved electrochemical performance.