Zirconia-Based Potentiometric Sensors Using Metal Oxide Electrodes for Detection of Hydrocarbons

The non-Nernstian behavior of zirconia-based electrochemical cells with various metal oxide electrodes for 0–500 ppm C1-C4 hydrocarbons, hydrogen, and carbon monoxide was studied in the presence of 10% oxygen at 600°C. The cell using an In 2 O 3 electrode exhibited a largely negative electromotive force (emf) for propene but gave moderately negative emfs for hydrogen and carbon monoxide. The addition of 0.1 wt % MnO 2 to the In 2 O 3 electrode significantly improved the selectivity of the parent electrode for propene over hydrogen and carbon monoxide. The negative emf of the cell using the MnO 2 -containing In 2 O 3 electrode for the hydrocarbons became enhanced as the carbon number of the hydrocarbon increased, the C-C linkage was unsaturated, and the chain structure was branched. This enhanced effect, as well as the addition effect of MnO 2 , was discussed on the basis of the measurements of the polarization curves of the MnO 2 -containing In 2 O 3 electrode for the hydrocarbons and oxygen and the nonelectrochemical oxidation of the hydrocarbons by oxygen. In addition, the MnO 2 -containing In 2 O 3 electrode for the hydrocarbons was compared with an Au electrode with respect to sensitivity to the hydrocarbons and reproducibility of the sensing properties.