Sensing behavior and mechanism of mixed potential NOx sensors using NiO, NiO(+YSZ) and CuO oxide electrodes

Abstract The mixed potential type NO x sensors using yttria stabilized zirconia (YSZ) electrolyte with various oxide electrodes were prepared and tested in NO x containing atmosphere at 700 °C. Among them, the sensors with CuO and NiO electrodes showed comparatively large responses to NO x . The sensor with CuO electrode has showed the good transient responses but smaller EMF signal than the sensor with NiO electrode, while the sensor with NiO electrode has showed sluggish transient behavior but larger signal than the sensor with CuO. Addition of YSZ particles to NiO electrode gave rise to an increase in EMF response as well as a fast response and a recovery. Based on the microstructure of electrode and its polarization curves, the sensing principle of this type sensor was studied and discussed. In addition, their sensing characteristics were examined in the mixture gas of NO 2 and NO through EMF measurement and I – V characteristics. The responses of the sensors were correlated with NO and NO 2 concentrations to elucidate the sensing mechanism of oxide electrode in contact with YSZ. From the relations between EMF and NO/NO 2 concentrations for each electrode, the measuring method to detect NO, NO 2 and total NO x concentrations was suggested.