CO2 / H2O co-electrolysis using Single and Stack Solid Oxide Electrolysis Cell (SOEC)

Abstract

The production of syngas by co-electrolysis using solid oxide electrolysis cells (SOECs) has been attracting attention as a highly efficient technology for converting CO₂ into useful compounds. However, co-electrolysis is complicated because the main electrolysis reactions and side reactions occur simultaneously. In this study, co-electrolysis of CO₂ and H₂O were conducted using a large size single cell with cell holder used for stack applications and also 3 cells stack. It was found that I-V curves was hardly dependent on the CO₂ and H₂O ratio in feed gas and thermal neutral voltage is also hardly changed, suggesting that the reverse water-gas shift (RWGS) reaction is the primary CO-producing reaction even in the larger size cells. So, the main electrolysis reaction was steam electrolysis occurred at three phase boundary and RWGS mainly occurred in gas phase with unconverted CO₂. Similar dependency was observed on the 3 cells stack indicating that the outlet gas composition and electrochemical properties exhibited similar dependency on CO₂ and H₂O ratio of the large single cell. This finding suggests that stacking multiple cells has minimal impact on the reaction mechanism or outlet gas composition, and that CO production occurred by RWGS reaction similar with the large single cell.