Planar, impedance-metric NOx-sensor with spinel-type SE for high temperature applications

This study displays the results obtained with planar, impedance-metric sensors having a NiCr2O4-sensing electrode (SE) and FYSZ or PYSZ (fully or partially yttria stabilised zirconia) electrolytes. The sensing electrodes of planar design sensors are fabricated by magnetron sputter technique. The evaluation of the microstructure and phase sequence of the sensing electrode is analysed. The sensing characteristics towards NO and O2/NO-gas mixtures of the sensor samples are analysed at temperatures up to 700 °C by varying the NO concentration between 0 and 1000 ppm and by adding 5 vol.% of O2. The cross-selectivity of the sensor samples to other flue-gases, such as CO2, CO and CH4 and the mixtures of those with O2 are also analysed. These analyses showed that the total impedance is a new and capable type of sensing parameter for the characterisation of NO-gas sensors. Thus, this study demonstrates the principal applicability of the impedance-metric sensor concept for the detection of NOx in lean atmospheres by applying the total impedance. The tested sensor samples are able to monitor NO up to 1000 ppm at 650 °C.