First-Principles Based Microkinetic Modeling of CO2 Reduction at the Ni/SDC Cathode of a Solid Oxide Electrolysis Cell

Understanding of the CO2 electroreduction mechanism at the three-phase boundary (TPB) is of great importance for the development of a solid oxide electrolysis cell (SOEC). In this study, the effect of oxygen vacancy locations on the CO2 reduction reaction (CO2RR) at the TPB of Ni(111)/samarium-doped ceria (SDC) surface was investigated using periodic density functional theory (DFT) + U calculations. It was found that interface oxygen vacancy can notably boost CO2 adsorption and reduction. Based on DFT results, a microkinetic analysis was conducted to determine the rate-controlling step under various solid oxide electrolysis cell operating voltages at 1000 K. Possible charge transfer steps, including one- or two-electron charge transfer, were considered and discussed. The analysis reveals that, on Ni/SDC with noninterface oxygen vacancy, the rate-controlling step will change from the oxygen spillover step to the CO desorption step with an increase in cathode overpotential. On Ni/SDC with interface oxygen vacancy, CO desorption is the rate-controlling step regardless of the electrode overpotentials.