A Comparative Study of the Performance and Electrode Processes of Solid Oxide H2O Electrolysis and CO2 Electrolysis

Solid oxide CO2 electrolysis was less studied compared with H2O electrolysis and the relevant reaction mechanism and electrode processes were poorly understood. This paper investigated the performance and electrode processes differences between CO2 electrolysis and H2O electrolysis. The shape of j-V curves, electrochemical impedance spectroscopy data and calculated distribution relaxation time results were analyzed. It was found that the performance of CO2 electrolysis degraded the most compared with that in SOFC mode and for H2O electrolysis after a 65 h’ operation. Meanwhile, j-V curve of CO2 electrolysis changed a lot and finally showed a convex total resistance pattern with applied current. It was also found that the characteristic frequency of charge transfer reaction and diffusion process for CO2 electrolysis was much lower than that of H2O electrolysis. A thermal activated peak at 10-100 Hz which was not noted for H2O electrolysis was considered to be CO2 adsorption and dissociation process in fuel electrode. Besides, diffusion process for H2O-H2 and CO2-CO mixture also differed. Finally, it was indicated that the different performance degradation may be due to different suppressed degree of charge transfer reaction in fuel electrode for H2O electrolysis and CO2 electrolysis and additional suppressed adsorption or dissociation process of CO2 for CO2 electrolysis.