Impedance Characterization of a Model Au∕Yttria-Stabilized Zirconia∕Au Electrochemical Cell in Varying Oxygen and NO[sub x] Concentrations

Abstract

An electrochemical cell serves as a model system to investigate the effect of and . Possible mechanisms responsible for the response are presented. Two dense Au electrodes are co-located on the same side of a dense YSZ electrolyte and are separated from the electrolyte by a porous YSZ layer, present only under the electrodes. While not completely understood, the porous layer appears to result in enhanced response. Impedance data were obtained over a range of frequencies , temperatures , and oxygen (2–18.9%) and concentrations. Spectra were fit with an equivalent circuit, and values of the circuit elements were evaluated. In the absence of , the effect of on the low-frequency arc resistance could be described by a power law, and the temperature dependence by a single apparent activation energy at all concentrations. When both and were present, however, the power-law exponent varied as a function of both temperature and concentration, and the apparent activation energy also showed dual dependence. Adsorption mechanisms are discussed as possibilities for the rate-limiting steps. Implications for impedancemetric sensing are also discussed.