Development of NOx sensing devices based on YSZ and oxide electrode aiming for monitoring car exhausts

Recent progress in the development of zirconia-based sensing devices using zinc-family oxide electrodes for both mixed-potential and complex impedance-based types has been focused on the detection of NOx in the temperature range 600-700 C. The sensing characteristics of these sensors were investigated in different gaseous environments. The mixed-potential-type NOx sensor using ZnFe2O4 sensing electrode (SE) have shown the highest sensitivity to NOx among other spinel-type oxides tested as SEs in the temperature range 600-700 C. The complex-impedance-based NOx sensor attached with ZnCr2O4-SE gave good sensing characteristics to NOx at 700 C. The sensitivity to NO is almost equal to the sensitivity to NO2 from 0 to 200 ppm for this sensor at 700 C. The observed NOx sensitivity and the measured NOx concentration had almost linear correlation even in the presence of 8 vol% H2O and 15 vol% CO2. Based on the results, a laminated-type sensor structure that is the best for the present complex impedance-based NOx sensor was proposed. 12 refs.