Production of syngas from H2O/CO2 by high-pressure coelectrolysis in tubular solid oxide cells

Abstract

The conversion of CO2 and steam into syngas in a pressurized solid oxide coelectrolysis (SOC) cell is considered one of the most promising pathways towards the production of sustainable fuels. In this study, a high pressure tubular SOC system was designed and developed that can efficiently convert a mixture of steam and CO2 into valuable syngas fuel. Tubular SOC cells based on a Ni-yttria stabilized zirconia (Ni-YSZ) fuel electrode, scandia stabilized zirconia (ScSZ) electrolyte, and La0.6Sr0.4Co0.2Fe0.8O3 (LSCF)-Ce0.8Gd0.2O1.9−δ (GDC) composite air electrode were fabricated and tested at various high pressure conditions to determine the electrochemical and syngas production characteristics. The pressurized tubular SOC cell was first operated at the ambient pressure for various inlet gas conditions and the electrochemical performance of the tubular SOC was studied by current-voltage curves combined with electrochemical impedance spectroscopy at different H2O and CO2 mole% in the inlet gas. The pressurized SOC cell was then operated between 1 and 8 bar pressure at 800 °C in both fuel cell and coelectrolysis modes. In the fuel cell mode, the SOC showed a 44.2% increase in the maximum power density to with a pressure increase of 1–8 bar. The increase in the performance of the cell in the fuel cell mode was attributed to the higher open circuit voltage (OCV) and reduced polarization resistance of the electrodes at higher pressures. In the coelectrolysis mode, the pressure dependency of the electrochemical characteristics on the tubular SOC cell was studied and the relation between different parameters of the system and the pressure conditions was derived. It was found that the higher open circuit voltage (OCV) and the reduced polarization resistance resulted in a significant improvement in the performance of the pressurized tubular SOC cell for the production of syngas. A post-test material characterization by electron microscopy did not show any significant degradation in the tubular SOC cell microstructure during the high pressure operation at 8 bar.