Influence of Thickness of Cr2O3 Sensing-electrode on Sensing Characteristics of Mixed-potential-type NO2 Sensor Based on Stabilized Zirconia

A planar NO2 sensor was fabricated by using a yttria-stabilized zirconia (YSZ) plate and Cr2O3 sensing-electrode (SE). The NO2 sensing performances were evaluated at 700°C in the presence of 5 vol.% water vapor for the sensor attached with each of Cr2O3-SE having different thicknesses. It was found that the NO2 sensitivity of the sensor was highest when the thinnest Cr2O3-SE was used and decreased with increasing thickness of SE. A linear correlation between the sensitivity and the NO2 concentration was observed at 700°C in the range of 50–400 ppm for each sensor. Based on the results of the measurements for the NO2 conversion to NO on each of Cr2O3 layers having different thicknesses, it was confirmed that the catalytic activity to the gas-phase NO2 decomposition on the Cr2O3-SE matrix played an important role in deciding the NO2 sensitivity of the present sensor.