Application of TiO2 to amperometric NOx sensors based on NASICON

• NASICON sensor realized by applying TiO2 catalyst to Pt electrode
• Linear response current attained for NO and NO2 concentrations of 0 to 1 ppm
• P25 produces the largest response current and shortest response time.
• Optimal applied voltage found to be − 200 mV
• Ideal working temperature found to be 150 °C

The work focused on improvement of the current response to NO and the reduction of response time of both NO and NO2. By adding a layer of TiO2 catalyst layer, the shortcoming of NO insensitivity of traditional NASICON based amperometric NO2 sensor was solved. TiO2 was known as an n-type semiconductor and a high-performance NO oxidation catalyst. We separately applied different types of TiO2 (rutile and Degussa P25) on the device and compared the test results with the traditional type without a catalyst layer. The results showed that the TiO2 attached device exhibited a significant improvement to NO response, and P25 was better than rutile TiO2 on account of the higher activity of anatase TiO2. In addition, TiO2 also played a role of a semiconductor electrode, resulting in the increase of response to NO2. The response time of NO and NO2 was separately shrunk from 153 s, 70 s to 77 s, 43 s owing to the P25 layer. The current responses were found to be barely affected by the coexistence of CO2.