A stabilized-zirconia-based NOx sensor attached with oxide sensing-electrode (SE) was tested for the detection of NOx at temperatures higher than 800degreesC for car-emission control applications. Among various oxide SEs tested, NiO was found to give the highest sensitivity to NO2 even at high temperatures. It was found that the sensor using NiO-SE showed quicker recovery in the presence of water vapor, compared with that in the dry sample gas. Electromotive force values of 57 and 75 mV were observed, respectively, under dry and wet (5 vol % water vapor) conditions with 400 ppm NO2 at 850degreesC. (C) 2004 The Electrochemical Society.