Abstract
The electrochemical oxidation of 
and CO in a 
system at the interface of a porous Ni‐yttria stabilized zirconia (YSZ) cermet electrode and YSZ electrolyte has been studied using complex‐impedance spectroscopy and direct‐current polarization measurements of 1023 and 1273 K under a constant oxygen partial pressure. The polarization resistance increased when the CO concentration ratio. 
, exceeded 0.2 and 0.5 at 1023 and 1273 K, respectively. The electrochemical oxidation rate of 
was 1.9–2.3 times and 2.3–3.1 times higher than that of CO at 1023 and 1273 K, respectively, and the water‐gas shift reaction was found to be much faster than the electrode reaction at both temperatures. An equivalent‐circuit analysis of the complex‐impedance spectra suggested that the lower electrochemical oxidation rate of CO (compared to 
) was caused mainly by the larger diffusion resistance of CO than 
on the electrode surface at 1023 K, and by both the larger surface diffusion resistance and charge‐transfer resistance at 1273 K. © 2000 The Electrochemical Society. All rights reserved.