Detection of VOC in air with a planar-type potentiometric gas sensor based on YSZ with a Pt electrode modified with TiO2

Abstract The half-cell potential of a Pt/YSZ electrode modified with TiO 2 was strongly dependent on the concentration of VOC in air. The experimentally estimated electron number in the Nernst relation for oxygen increased from 2.0 to 4.0 with increasing temperature from 400 to 600 °C. For the TiO 2 -Pt/YSZ electrode at 400 °C, the following three processes are proposed: [1] O 2(gas)  ⇔ O 2(ad) /TiO 2 , [2] O 2(ad) /TiO 2  + 2e −  ⇔ 2O − (ad) /TiO 2 , and [3] 2O − (ad) /TiO 2  + 2e − /Pt → 2O 2− (ad) /Pt. The half-cell potential of the TiO 2 -Pt/YSZ electrode is expressed as E = (RT/2F) ln [O 2(ad) /TiO 2 ]. The concentration of the adsorbed oxygen is estimated using a combination of a competitive adsorption model for a mixture of oxygen and VOC and oxidation of the adsorbed VOC with the adsorbed oxygen. Numerically estimated potentials of the TiO 2 -Pt/YSZ electrode are reliable qualitatively for the VOC concentration dependence of the potential. The electrode potential of the sensor with a pristine Pt electrode and the modified electrode with TiO 2 responded to the ppm level of VOCs in air.