Preparation And Properties Research Of Sensing Electrode Materials For NO_x Sensor Of Vehicles

With the rapid development of the vehicle industry, the exhaust pollution becomesmore and more serious. In order to reduce the emission of NO_x in the exhaust, strictemission standards have been issued by most countries,and NO_x sensor is essentialsensing element for controlling the car exhaust.Therefore, it’s extremely urgent to exploita NO_x sensor with high sensitivity, perfect selectivity and reliable performance. Currently,the researches on NO_x sensor mainly focus on electrode materials.This thesis focuses on the electrode material of NO_x sensor, and mainly studied theperformance of the electrode sample made by doping WO₃.into NiO and Cr₂O₃.Ourspecific works are as follows:Obtain NiO,Cr₂O₃and WO₃powder with small particle size and uniform disperseusing nickel nitrate, chromic nitrate and ammonium tungstate as raw materials. The resultsof the research show that: homemade electrode material powder have narrow particlesize distribution,small particle size, high specific surface area; the special sinteringtemperature of WO₃powder is not fit to be used as electrode materials.Preparing the electrode slurry by doping WO₃into NiO, and screen printing themonto YSZ substrate. Then sinter the substrate into thick electrode membrane underdifferent temperatures, and thus make them into electrode samples. We have studied theaffect of sintering temperature and the doping amount of WO₃on the NO sensingcharacter. Theresults of t he research show that: WO₃doping can change themicrostructure of NiO electrode: the sublimation in the form of free state WO₃generate loose porous, NiWO₄precipitation hindered growing up of the grain; appropriateWO₃doped NiO electrode material on the potential response rate and NO responseamplitude can be increased obviously. In the condition of electrode sintering temperatureof1000℃, the optimal doping amount WO₃for20wt.%; and20wt.%WO₃dopingNiO electrode preparation of electrode sample engenders26.78mV of NO response potential,the potential value is2times higher than pure NiO electrode sample in thesame testing condition.Preparing the electrode slurry by doping WO₃into Cr₂O₃., and printing them ontoYSZ substrate by screen printing. Then the electrode are sintered into thick electrodemembrane under different temperatures, and thus make them into electrode samples.Based on the electrode surface morphology and physical phase analysis, and combinedwith impedance spectrum test results,We have studied the affect of sintering temperatureand the doping amount of WO₃on the response potential and recovery characteristics ofresponse. The results of the research show that: the best sintering temperature of Cr₂O₃electrode sample is1000℃, in this sintering temperature, the electrode has bettermicrostructure and electric catalytic activity than other temperature; the electrode sampleof10wt.%WO₃doping Cr₂O₃preparation give NO response potential for29.84mV at500℃for500ppm, however the response potential for pure Cr₂O₃electrode sampleis only11.96mV in the same condition, the response potential value increase nearlythree times.The result is mainly produced by the electrode surface microstructure.