Performance evaluation of SOEC for CO2/H2O co-electrolysis: Considering the effect of cathode thickness

Abstract

Solid oxide electrolysis cells (SOECs) provide a great opportunity to stabilize carbon dioxide (CO2) emissions by converting CO2/H2O into synthetic fuels with high energy conversion efficiency. Nevertheless, the performance of state-of-the-art Ni-cermet supported SOEC is limited by the interfacial polarization resistance. This study presents a simple approach to minimize the cathodic polarization resistances by reducing its thickness. The effect of cathode thickness on the electrochemical performance of SOECs for CO2/H2O co-electrolysis are investigated at 750–850 °C for variable reactant gas composition. Electrochemical measurements like current density-voltage (i-V) curves and electrochemical impedance spectroscopy (EIS) are performed to characterize the performances of the cells. Impedance spectra are recorded under open circuit voltage (OCV) and polarization (1.4 V) to deeply study the influence of cathode thickness on polarization loss processes. The EIS results confirm that when reducing the cathode thickness, the cathode activation polarization is slightly decreased, whereas, the concentration polarization is significantly reduced, improving the reactant gas diffusion and the performance of SOEC. A similar effect is observed by increasing the CO2 mole fraction in the feed. Furthermore, the variation of cathode thickness and gas composition greatly affected the cell performance at high temperature, due to large reactants utilization. The results reveal that SOEC performance for co-electrolysis of CO2/H2O could considerably be improved by reducing the cathode thickness and improving the transport processes within the fuel-electrode. These results aid the optimization of cell design to improve the gaseous transport to the electrode/electrolyte interface and enhance the performance of SOEC for CO2/H2O reduction.