Solid-state potentiometric SO2 sensor combining NASICON with V2O5-doped TiO2 electrode

A compact tubular sensor based on NASICON (sodium super ionic conductor) and V2O5-doped TiO2 sensing electrode was designed for the detection of SO2. In order to reduce the size of the sensor, a thick-film of NASICON was formed on the outer surface of a small Al2O3 tube; furthermore, a thin layer of V2O5-doped TiO2 with nanometer size was attached on the NASICON as a sensing electrode. This paper investigated the influence of V2O5 doping and sintering temperature on the characteristics of the sensor. The sensor attached with 5 wt% V2O5-doped TiO2 sintered at 600 °C exhibited excellent sensing properties to 1–50 ppm SO2 in air at 200–400 °C. The EMF value of the sensor was almost proportional to the logarithm of SO2 concentration and the sensitivity (slope) was −78 mV/decade at 300 °C. It was also seen that the sensor showed a good selectivity to SO2 against NO, NO2, CH4, CO, NH3 and CO2. Moreover, the sensor had speedy response kinetics to SO2 too, the 90% response time to 50 ppm SO2 was 10 s, and the recovery time was 35 s. On the basis of XPS analysis for the SO2-adsorbed sensing electrode, a sensing mechanism involving the mixed potential at the sensing electrode was proposed.