Revealing the Reaction Mechanism of CO2/H2O Coelectrolysis on Perovskite-Based Cathode Materials

High temperature solid oxide fuel cells (SOECs) have attracted widespread attention in recent years due to their high energy conversion efficiency. CO2/H2O coelectrolysis through SOEC can simultaneously realize electrochemical energy storage and effective utilization of CO2. However, the reaction mechanism of coelectrolysis is still unclear. In this study, a Sr2Ti0.8Co0.6Fe0.6O6−δSm0.2Ce0.8O2−δ composite cathode is used as a model system to investigate the effect of applied voltage on coelectrolysis and the reaction pathway of coelectrolysis. The current density, syngas generation rate increases, and H2/CO ratio in produced syngas are found to increase with the applied voltage. An electrochemical test reveals that the applied voltage can effectively facilitate the gas diffusion in porous electrodes, hence promoting the coelectrolysis process. The electrochemical response, electrolysis products, and surface chemistry of the electrode for CO2/H2O coelectrolysis are compared with those for CO2 electrolysis and H2O electrolysis. The results suggest that during coelectrolysis, H2O electrolysis to produce H2 dominates, and CO is primarily generated through the reverse water gas shift. Finally, the long-term stability of the electrode for CO2/H2O coelectrolysis is investigated, and the causes for the degradation of the cell performance are proposed to the changes of the electrode microstructure. The results provide critical insight into the reaction mechanism of coelectrolysis and can help guide the development of high-performance electrode materials for SOECs.