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

The mixed potential type NOx sensors using yttria stabilized zirconia (YSZ) electrolyte with various oxide electrodes were prepared and tested in NOx containing atmosphere at 700 °C. Among them, the sensors with CuO and NiO electrodes showed comparatively large responses to NOx. 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 NO2 and NO through EMF measurement and I–V characteristics. The responses of the sensors were correlated with NO and NO2 concentrations to elucidate the sensing mechanism of oxide electrode in contact with YSZ. From the relations between EMF and NO/NO2 concentrations for each electrode, the measuring method to detect NO, NO2 and total NOx concentrations was suggested.