Characterization of a Nickel / Gadolinia Doped Ceria Fuel Electrode for Co-Electrolysis

Abstract

Modelling of the co-electrolysis process requires understanding of the underlying reaction pathways. These include the electrochemical steam reduction, the electrochemical CO2 reduction and their coupling via the catalytic (reverse-)water-gas-shift reaction (RWGS). The assumption of a very fast water-gas-shift reaction and therefore neglectable CO2 electro-reduction is commonly used to model the co-electrolysis process. In contrast to that, it was proposed from previous studies, that the electrochemical conversion of CO / CO2 can be present under H2 / H2O / CO / CO2 gas mixtures on Ni/GDC fuel electrodes. We present results from a complex variation of operating parameters for process identification by the use of electrochemical impedance spectroscopy and the subsequent impedance analysis by the distribution of relaxation times (DRT). Four peaks are identified, including one yet undocumented suspected gas diffusion process. A possible influence of the electrochemical conversion of CO/CO2 starting from pCO2 / pH2O > 1 is shown.