Effect of the PH2O/PCO2 and PH2 on the intrinsic electro-catalytic interactions and the CO production pathway on Ni/GDC during solid oxide H2O/CO2 co-electrolysis

Abstract

The study presents a holistic methodology for the discrimination of the contribution of H2O and CO2 electrolysis reactions, as well as of the RWGS, on the production rate of CO during the solid oxide H2O/CO2 co-electrolysis process. The investigation took place on an electrolyte supported cell with Ni/GDC as the fuel electrode, at 800–900 °C, by applying various PΗ2Ο/PCO2 feed ratios, in the range of 0 ≤ PΗ2Ο/PCO2 ≤ 1, and two PΗ2 values (2 and 21 kPa). Critical combination of physicochemical and electrochemical characterization with electrocatalytic measurements and quantitative analysis of products highlighted a competitive adsorption and electro-reduction between H2O and CO2 on Ni/GDC. Moreover, it is confirmed that the H2O/CO2 co-electrolysis process is determined by: (i) PH2O/PCO2 ratio and (ii) PH2. Specifically, at PΗ2Ο/PCO2 = 1 and high PΗ2 = 21 kPa the adsorption of H2O is favored, compared to CO2, and the electrochemical process is 100% selective towards the electrolysis of H2O. The CO production is catalytically controlled by the RWGS reaction. The electrochemical reduction of CO2 occurs at PΗ2Ο/PCO2 = 0.3, in combination with H2O electrolysis and the RWGS, whereas its contribution is enhanced by decreasing the PΗ2Ο and PΗ2.