| The development of technology promotes the rapid development of all walks of life, especially in the automotive industry. The increase in the number of car exhaust emissions also increased, resulting in the contamination of the environment and energy consumption. In order to save energy, reduce HC and CO emissions and other harmful gases, gasoline engine electronically controlled fuel injection system (EFI) toward the lean-burn control technology upgrades. But this brings generation of harmful NOx gases, thus gave birth to the demands NOx gas sensor. Wherein, the NOx gas sensor based on yttria-stabilized zirconia (abbreviated YSZ) solid electrolyte mixed potential-type NOx gas sensor has a simple structure, without reference gas, large test gas range, the output potential easy to be measured, etc., so that the sensor becomes the research focus of vehicle sensor. In this paper, the sensitive characteristics of planer zirconia-based mixed-potential-type NO2 sensors with perovskite-type LaFeO3, LaCrO3, LaNiO3 and WO3 as sensing electrodes were studied, and in order to improve the detection limit of the sensor and sensitive characteristics connecting the planer sensors in series to array sensor.In the first part, the research progress of the gas sensor was introduced in the first, and then the characteristic of the sensitive materials and the mechanism of the mixed-potential-type solid electrolyte NOx gas sensors. After that, the AC impedance spectroscopy testing technology was presented in the study of solid electrolyte gas sensor. At last, the research content of this article was introduced.The sensitive materials with the perovskite structure are mainly studied in the second part, focusing on the preparation and gas sensing properties of LaFeO3, LaCrO3 and laNiO3.In this chapter, the perovskite-type oxides, such as LaFeO3 and LaCrO3,were prepared by the solid phase synthesis; in addition, LaNiO3 was also prepared by the citric acid decomposition method. At the same time, we analyzed the phase composition and microstructure of these perovskit-type oxides by XRD and SEM measurements. On this basis, planar mixed-potential-type NO2 sensor using yttria-stabilized zirconia (YSZ) and the three oxides with perovskite structure sensing electrode was fabricated by means of screen-printing method. Their characteristics of EMF and response time were studied in the different NO2 concentration and temperature. The results showed that the sensor have a good sensitive characterization in the temperature ranges from 600 ℃ to 700 ℃. The output forces rise with the increase of NO2 gas concentrations, and the present sensor is found to give a linear correlation between EMF and the logarithm of NO2 concentration from 30ppm to 50ppm.Besides, the EMF and the sensitivity of the sensor decreased with the increase of the temperature. Moreover, the sensitive characteristics and sensitivity of the sensors with the three oxide materials are different, and the result is as follows:LaNiO3>LaFeO3>LaCrO3.In the chapter three, the sensitive properties of the sensor with WO3 sensitive electrode material and YSZ solid electrolyte in sub-ppm level NO2 gas was studied. The results show that the sensor for sub-ppm level NO2 gas has good sensing performance at the operating temperature. The present sensor showed a good linear relationship between the output potential and the logarithm of NO2 gas concentration in the concentration range 125ppb～625ppb at 500～600℃, but the EMF and the sensitivity decreases with increasing temperature.In chapter four, the sensitive performance of the array sensors in series with WO3 electrode and YSZ solid electrolyte were researched. The research results showed that the sensors present have good characteristics in sub-ppm level NO2 concentration at high temperature; the EMFs and sensitivities decrease as the increasing temperature in the same NO2 concentration. The sensors showed a linear relationship between the output potential and the logarithm of NO2gas concentration at 500～600℃. At the same temperature, the response value increase with the increasing of the sensor number. The result of measurement declared that the repeatability of the sensor is very good, but the stability is not good, the signal noise ratio is relatively large. The response time of the array sensor is long, about 10min, and the recovery time is shorter than the transient response time.The last part of the paper is the conclusions of this article, which summarizes the innovation theory and the experimental of the full text, and also pointed out the disadvantages and the areas need to improvement in the experimental. |
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