Solid-state amperometric NO2 sensor using a sodium ion conductor

A solid-stare amperometric sensor for NO2 was newly designed by combining a Na+ conductor (NASICON) with NaNO2 (or NaNO3) auxiliary layers deposited on both sensing and counter electrodes. The potential of the sensing electrode was polarized at a constant value, by referring to the reference Au electrode, and the electric current between the sensing and counter electrodes was measured as a sensing signal. It was found that the NaNO2-attached device gave a much higher NO2 sensitivity at 200 degrees C than the NaNO3-attached device. The current response of the NaNO2-attached device was almost linear with the NO2 concentration in the range of 0-80 ppm. In addition, it was demonstrated that the sensitivities of the device to various other gases, such as NO, CO, H-2, CO2, CH4 and H2O, were very small compared to that to NO2 and the device could be operated rather stably during the test period of ca. 40 days except for a few days in the early stage. Based on the sensing performances obtained, the sensing mechanism of the device is briefly discussed.