High-temperature hydrocarbon sensors based on a stabilized zirconia electrolyte and proton conductor-containing platinum electrode

The non-Nernstian behavior of zirconia-based oxygen sensors for 0-1000 ppm C1-C5 hydrocarbons, carbon monoxide, and hydrogen was studied using various ion conductor-containing Pt electrodes in the presence of 10 vol.% of oxygen at 600 degreesC. The addition of a proton conductor, especially SrCe0.95Yb0.05O3-alpha (SCY), to the Pt electrode improved the sensitivity for the hydrocarbons over other reducing gases: -122 mV for 1000 ppm propene; -24 mV for 1000 ppm carbon monoxide; and -23 mV for 1000 ppm hydrogen. The EMF value of the cell was enhanced by the increasing carbon number of the hydrocarbons, the unsaturation of the C-C linkage, and the branching of the chain structure. A similar conclusion also applied to aromatic hydrocarbons: -81 mV for 500 ppm benzene; -96 mV for 500 ppm toluene; and -102 mV for 500 ppm p-xylene. This enhanced effect, as well as the addition effect of SCY, was discussed on the basis of the measurements of polarization curves for hydrocarbons and oxygen and the non-electrochemical oxidation of the hydrocarbons by oxygen. It was found that the added SCY did not inhibit the catalytic activities for the hydrocarbons, but decreased the cathodic reaction rate of oxygen, thus, shifting the mixed potential for the hydrocarbons to more negative values. (C) 2001 Elsevier Science B.V. All rights reserved.