Stabilized zirconia-based NOx sensor using ZnFe2O4 sensing electrode

A tubular sensor using yttria-stabilized zirconia (YSZ) and a spinel-type oxide sensing-electrode (SE) was fabricated and examined for NOx detection at high temperatures. Among spinel-type oxides tested and reported in the literature to date, ZnFe2O4 has the highest sensitivity to NO2 in air at temperatures of 550-700 degreesC. In this temperature range, the electromotive force (emf) response of the sensor was almost linear to the logarithm of NO or NO2 concentration in the range from 25 to 436 ppm. Scanning electron microscopy and X-ray diffraction analysis were used to examine the morphology and crystalline structure of the ZnFe2O4 film. Investigation of the sensor stability showed that the output emf to 100 ppm NO2 have been gradually increased within similar to 20% range after similar to 20 day operation up to 200 days examined at 700 degreesC in dry synthetic air. The air base has been stable during the whole test period. (C) 2001 The Electrochemical Society.