Potentiometric NOx sensor based on stabilized zirconia and NiCr2O4 sensingelectrode operating at high temperatures

The two types of electrochemical sensors using stabilized zirconia and the oxide sensing electrode (SE) were developed for NOx detection at high tempe ratures. For the mixed-potential-type sensor, NiCr2O4 was found to give fai rly excellent NOx sensing characteristics in air among several spinel-type oxides tested. This NO, sensor provided a linear correlation between EMF an d the logarithm of NO or NO2 concentration in the range 25-436 ppm and in t he temperature range 550-650 degreesC. With fixed bias voltage being applie d between the SE (oxide) and the counter (Pt) electrode (CE), the EMF betwe en SE and the reference (Pt) electrode (RE) was measured as a sensing signa l. The NiCr2O4-attached tubular device was found to provide selective respo nse to NO over NO2 if SE was polarized at +175 mV versus RE. It was also fo und that this device gave selective response to NO2 over NO, if SE was pola rized at -250 mV versus CE. The new design of the planar device was propose d to avoid the cross-sensitivities to the others gases usually coexisting i n car exhausts. (C) 2001 Elsevier Science B.V. All rights reserved.