Sensing properties and selectivities of a WO3/YSZ/Pt potentiometric NOx sensor

Sensing properties of a WO3-based potentiometric NOx sensor were investigated in both N2 and simulated exhaust gas. A positive voltage response was obtained for NO2 but negative for NO at 650 °C with the n-type semiconducting WO3-based sensor. The sensor was able to selectively detect NO in the presence of CO2 in 3% O2 and at 650 °C. The NO sensitivity, however, was affected by the variation of NO2, CO, and H2O concentration. At the same condition, the sensor had high sensitivity to ≈10 ppm NO2 and selectivity in the presence of CO, CO2, and H2O, showing it to be applicable to the monitoring of NO2. Significantly different sensing properties of NO in simulated exhaust gas suggested the occurrence of gas composition change by the gas-phase and gas–solid reactions, and strong adsorption of water on the electrodes. The NO2 sensitivity in simulated exhaust gas was modified by O2 and H2O, but not by CO and CO2.