Reaction of CO/CO₂ gas mixtures on Ni-YSZ cermet electrodes

The reaction of carbon monoxide/carbon dioxide mixtures on Ni-YSZ cermet electrodes was investigated as a function of the electrode potential and the partial pressures of the reactants at 1273 K. Time-dependent reaction rates are observed for the CO oxidation reaction for oxygen activities corresponding to open circuit potentials in the range from -750 to -1010 mV. The electrode changes between a passive state and several active states for the CO/CO₂ reaction. Periodic changes of the reaction rate for the CO oxidation are observed every 30 and 80 s. The impedance spectra recorded at the rest potential and the overpotential dependence of the CO oxidation rate indicate a change in the number of active sites in the reaction zone. In the active state, the CO oxidation reaction is more than one order of magnitude slower than the hydrogen oxidation reaction on these Ni-YSZ cermet electrodes. These results indicate clear differences in the kinetics of the CO and H₂ oxidation reaction.