Carbon dioxide reduction on gadolinia-doped ceria cathodes

AC impedance spectroscopy has been performed on 40 mol% gadolinia-doped ceria electrodes on yttria stabilized zirconia (YSZ) at 700–950 °C in reducing CO/CO2 atmospheres. Area-specific-resistance (ASR) values for this electrode were in the range of 0.8–37 Ω-cm2, about two orders of magnitude lower than measurements on Pt electrodes and slightly lower than data on Ni-YSZ electrodes in the literature under similar temperature and partial pressure of oxygen (PO2) conditions. A continuum-based model of this electrode is described and an analysis performed to extract the vacancy diffusion coefficient (Dv) and surface exchange rate coefficient (R0R0) as a function of temperature and PO2, from the impedance results. The Dv data agree reasonably well with published measurements of the tracer diffusion coefficient (D⁎) based on isotope profiling by secondary ion mass spectroscopy (SIMS) and conductivity measurements on 40 mol% GDC. The R0R0 values are a factor of 3 lower than the published measurements of the surface reaction rate (k) obtained from isothermal thermogravimetric relaxation, and decrease with increasing PO2. Values of the thermodynamic factor (A) calculated from the fitted model parameters matched well with those calculated from oxygen non-stoichiometry data in the literature.