A planar NO2 sensor was fabricated by using yttria-stabilized zirconia (YSZ) and NiO sensing electrode (SE). The NO2 sensing characteristics of the sensor were examined for emission control applications at elevated temperatures. The planar sensor employing the 1300 degrees C-sintered NiO-SE could detect NO2 selectively even at 900 degrees C under wet condition, with acceptable NO2 sensitivity as well as response/recovery rates. The emf output of the sensor varied linearly with NO2 concentrations on a logarithmic scale in the range of 50-400 ppm. The sensing mechanism based on mixed potential for the present sensor was verified by means of polarization measurements. (c) 2005 Elsevier B.V. All rights reserved.