High-temperature NOx sensors using zirconia solid electrolyte and zinc-family oxide sensing electrode

Yttria-stabilized zirconia (YSZ) electrochemical sensors attached with the zinc-family oxide (ZnFe2O4 and ZnCr2O4) sensing electrode (SE) were fabricated and examined for NOx sensing properties at high temperatures. These oxide-SE-attached devices gave a linear correlation between EMF and the logarithm of NO2 (or NO) concentration from 50 to 436 ppm in the temperature range 600–700 °C. The sensor using the combination of ZnFe2O4 and ZnCr2O4 was found to give the highest sensitivity to NO2 in air at 700 °C among the oxide-SEs tested and reported in the literatures to date. Furthermore, addition of Pt to ZnFe2O4 was found to improve the sensing characteristics towards quick response. It was confirmed that the sensing performances to NO2 were roughly related to those to O2 for the devices tested here.