MEASUREMENT OF PT ELECTRODE SURFACE-AREA OF AUTOMOTIVE ZRO2 OXYGEN SENSORS

Platinum loading and metal dispersion have been measured in the outer, sensing electrodes of four commercial heated exhaust-gas oxygen (HEGO ) sensors which have previously been thoroughly characterized. The Pt dispersion is determined by methanation of adsorbed CO with H-2 With t he quantification of the CH4 formed in the process by a flame ionizati on detector. The outer electrodes differ by a factor of four in Pt loa ding. The lowest loading is noted on the sensor that is inert in the o xidation of small saturated hydrocarbon molecules under the evaluation conditions of the previous characterization. In all sensors the dispe rsion of the Pt is very low, with only 1-3 atoms in 10(3) directly acc essible to the gas phase. This technique is applicable to other gas se nsors that similarly contain noble metal additives with a very low sur face area.