The Fabrication And Study Of Amperometric Sensors Used In Testing NO_x In Atmosphere

The sharply increase of vehicle ownership in China and the power plant facilities have caused serious environmental problems. High concentration of NOx in the atmosphere may harm the respiratory system and if the circumstance is serious, there will cause pulmonary edema. The available measure used in testing the concentration of NOx in the atmosphere is sampling in the target place and determine the concentration of NO2 and NO by chemical methods in the lab. This method is very simple and the results are often very precise, but the disadvantage is that it's inefficient and the cost is very high, and the tests last for a long time and can't be used on the spot. What's more, the NOx concentration in the atmosphere is changeable, which makes the results a little valueless.The nitrogen oxides are emitted into the atmosphere in the form of NO. Gradually, part of NO will be oxidized to NO2, and finally they form a dynamic balance, the NOx in the atmosphere consist both NO and NO2. An amperometric gas sensor attached with NaNO2 in the counter electrode can detect the ppb level NO2, but it fails to detect the low concentration of NO in the air.In this article, we successfully synthesis the NASICON powder by high temperature solid state reaction, the conductivity and the purity of this material is very high. We finally chose NaNO2 as the sodium electrode material by comparing the response current of four amperometric sensors equipped with different sodium electrode materials. To solve the problem of the NO insensitive of the NASICON-based sensor, we adopted a layer of catalyst layer in the sensing electrode, which oxidize NO into NO2, so the test of total NOx become the test of NO2 by using this method. The results show that a layer of n type semiconductor can increase the current to NO2. We chose WO3, rutile TiO2 and Degussa TiO2 as three different catalyst materials, and compared the response currents of three sensors. P25 equipped sensor turned out to be the best among the three, the response currents to 1ppm NO2 and NO are separately 490nA and 570nA, the conversion rate of NO reached 86%, which is the highest in the three. In addition, the response current to interference gas like CO2 and vapor is very low, and the response time to NO and NO2 is significantly shortened.