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

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.