This study displays the results obtained with planar, impedance- metric sensors having a NiCr2O4- SE and a specially manufactured FSZ and PYSZ electrolytes. The fabrication of the sensor devices and their micro structural properties are analysed and their gas sensing properties under lean-burn conditions towards NOx are characterized. Therefore the sensing characteristics to NO and to O2/NO-gas mixtures are analysed at temperatures up to 700°C and at NO concentrations between 0 and 1000 ppm at the presents of different O2 concentrations. The cross-selectivity to other flue-gases, like CO2, CO and CH4 and mixtures of those with O2 are also analysed. The analysis shows that the total impedance is a new and capable type of sensing parameter for the characterisation of NO-gas sensors. This study applies the total impedance to demonstrate the principal applicability of impedance metric sensor concept for the detection of NOx in lean atmospheres and under harsh conditions. The tested sensor device is able to monitor NO up to 1000 ppm at 650°C.
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