Dependence of NO2 sensitivity on thickness of oxide-sensing electrodes for mixed-potential-type sensor using stabilized zirconia

The effect of thickness of oxide-sensing electrode (SE) on NO2 sensitivity of the planar sensor based on yttria-stabilized zirconia (YSZ) was examined at high temperatures. The sensitivity of the sensor increased with decreasing thickness of SE, and the highest sensitivity was obtained by using the thinnest layer of Cr2O3–SE (2.7 μm) at 700 °C. In the case of NiO–SE, the highest sensitivity was observed for the sensor using the 4-μm-thick SE even at a high temperature of 850 °C. Based on the results of the measurements for the complex impedances, the polarization curves, and the gas-phase NO2 decomposition catalysis, it was confirmed that the catalytic activity to the gas-phase NO2 decomposition on the oxide–SE matrix played an important role in determining the NO2 sensitivity of the present sensors.