SOLID-STATE AMPEROMETRIC NO2 SENSOR USING A SODIUM-ION CONDUCTOR

A solid-stare amperometric sensor for NO2 was newly designed by combin ing a Na+ conductor (NASICON) with NaNO2 (or NaNO3) auxiliary layers d eposited on both sensing and counter electrodes. The potential of the sensing electrode was polarized at a constant value, by referring to t he reference Au electrode, and the electric current between the sensin g and counter electrodes was measured as a sensing signal. It was foun d 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 concentratio n 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 d evice 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 p erformances obtained, the sensing mechanism of the device is briefly d iscussed.