Carbon monoxide/carbon dioxide electrochemical conversion on patterned nickel electrodes operating in fuel cell and electrolysis cell modes

• Patterned Ni electrodes characteristics of SOEC/SOFC in CO/CO2 atmospheres.
• Electrochemical kinetics varying voltage, temperature, partial pressure of CO and CO2.
• Surface diffusion rate determining steps.

Patterned Ni electrodes on single-crystal YSZ are applied as the fuel electrode for solid oxide cells (SOC) to investigate the electrochemical performance in CO/CO2 atmospheres in this paper. Patterned Ni maintains stable and intact during the whole test at high temperature (600 °C–700 °C). The polarization curves and EIS are measured with different operating voltages, temperatures, partial pressure of CO and CO2. The experimental results indicate that the patterned Ni electrode in SOEC mode performed a positive correlation with temperature, partial pressure of CO and CO2. The influence of partial pressure of CO2 is very weak, mainly due to the limited adsorption sites of CO2 on patterned Ni electrode. Besides, the rate of electrochemical reduction of CO2 is obviously slower than that of electrochemical oxidation of CO at the same temperature and gas component. Surface diffusion has a much greater effect on SOEC than on SOFC, especially when polarization voltage is small. Finally, a simplified reaction mechanism of CO2 electrolysis is proposed. The rate determining step of CO2 reduction on patterned Ni electrode could be the charge transfer reaction O(Ni) + (YSZ) + 2e− → O2−(YSZ) + (Ni). When the polarization voltage of electrolysis is small, the surface diffusion of O(Ni) also could become rate co-determining.