Semiconducting metal oxides as electrode material for YSZ-based oxygen sensors

The purpose of this research was to explore the effects of semiconducting metal oxides such as Ce0.75Zr0.25O2 (Ce–Zr), Ti0.75Zr0.25O2 (Ti–Zr), Zn0.75Zr0.25O2 (Zn–Zr), and Sn0.75Zr0.25O2 (Sn–Zr), on the performance of YSZ-based oxygen sensors. The semiconducting metal oxides used were prepared by a combustion method and then doped with 1.0 wt.% Pt by impregnation method. The sensors were exposed to synthetic exhaust gases with λ values in the range of 0.8–1.2. The sensors fabricated by Ce0.75Zr0.25O2 and Ti0.75Zr0.52O2 were shown to be independent of temperature variations and their low–high transitions took place just at about λ = 1. The sensor based on Zn0.75Zr0.25O2 also exhibited its transition at λ = 1, but its performance was affected by temperature changes. The behavior of the sensor based on Sn0.75Zr0.25O2 was observed to be temperature dependent and also its transition occurred at λ different from 1. By doping with Pt, the dependence of the sensors on temperature was eliminated to a large extent. Furthermore, the low–high transition for the sensors with λ different from 1 shifted to λ very close to 1. In fact, the presence of platinum reduces the boundary layer which in turn improves the ion conductivity of the sensor.