Production of synthesis gas (H2 and CO) by high-temperature Co-electrolysis of H2O and CO2

Abstract

The present work is focused on production of H2 and H2/CO-rich mixtures by electrolysis and co-electrolysis in Solid Oxide Electrolysis Cell (SOEC)-based stacks. The stack consists of 6 anode supported cells. Measurements are performed on a proprietary test bench designed to test stacks in the power range of 20–200 W. The performance of the stack is initially investigated in SOFC-mode, performing current-potential polarization curves in the range 650 °C–750 °C. After that the stack was tested under the reverse mode (SOEC, Co-electrolysis measurements are performed at 750 °C using a gas mixture containing different CO2/(H2+H2O) ratios. In order to investigate the influence of the operating parameters and fuel composition on the relative amounts of H2, CO and CO2 produced in the stack, a gas chromatography is used to analyze the composition of downstream gases after H2O condensation. As expected, the amount of H2 in the mixture increases with the increase of current density. The conversion of CO2 to CO increases linearly with the current density but it is quite insensitive to CO2 concentration in the cathode atmosphere. The concentration of CO2 affects the overall electrochemical performances of the stack by allowing to operate at higher current density but, however, a large part of CO2 seems to remain unreacted.