Current-Voltage Characteristics of Various Metal Electrodes in Limiting-Current-Type Zirconia Cells Application to Hydrocarbon Sensors

The influence of electrode materials on the current vs. voltage characteristics of limiting-current-type zirconia cells has been investigated systematically. The cells have one or two pairs of electrodes consisting of Pt, Pd, Au, or Ag, and a cover with a pinhole, which serves to limit gas diffusion and, therefore, the electrical current of the cells. The limiting current was found to depend definitely on the catalytic activity of the electrodes for the oxidation reaction of hydrocarbon gases in oxygen and hydrocarbon-containing gases. The results were applied to improve the sensitivity of limiting-current hydrocarbon sensors. The highest sensitivity was attained for the following combination of electrodes: Pt and Ag inner electrodes and a Au outer electrode in two-inner-electrode sensors. A preliminary examination has also been made on a three-inner-electrode sensor.