Experimental clarification of the R.W.G.S. reaction effect in H2O/CO2 SOEC co-electrolysis conditions

摘要

High temperature co-electrolysis of steam/CO2 mixtures using Solid Oxide Cells has been proposed as a promising technology to produce synthesis gas (H2 + CO) which can be processed further towards synthetic hydrocarbon fuels production. Co-electrolysis is a significantly more complicated process than steam electrolysis, because three reactions take place simultaneously; namely H2O electrolysis, CO2 electrolysis and the catalytic Reverse Water Gas Shift reaction (RWGS). Specifically, there are discrepancies whether CO is produced via the RWGS solely and that no electrolysis of CO2 occurs, or if CO is produced both via the RWGS and via electrolysis of CO2. As a result, it is crucial to quantify the degree of CO production for each reaction. In the presented investigation modified X-Ni/GDC electrodes (where X = Au, Mo and Fe) are studied, in the form of half-electrolyte supported cells, for their performance in the RWGS through catalytic-kinetic measurements. The samples were tested at open circuit potential conditions in order to elucidate their catalytic activity towards the production of CO (r_(co)), which is one of the products of the H2O/CO2 co-electrolysis reaction. In brief, it was found that the rate of the produced CO (r_(co)) increases by increasing the operating temperature and the partial pressure of H2 in the reaction mixture. In addition, the first results revealed that Fe-modification enhances the catalytic production of CO, since a 2wt.%Fe-Ni/GDC electrode proved to perform better, compared to all other modified electrodes and Ni/GDC, in the whole studied temperature range (800-900 °C) and for all studied reaction mixtures. The electrocatalytic investigation on electrolyte-supported cells is currently in progress.