Research On The Preparation Of Na_0.5Bi_0.5TiO₃ Solid Electrolyte And Performance Of NO_x Sensor Based On NBT

CO,HCx and NOx which come from automobile exhaust emission are the main resources of atmospheric pollution,and NOx is the most dangerous one which has caused heavy harm to the environment as well as the health of animals and plants.Recently,the demands of reliable sensors to detect NOx precisely are becoming increasingly higher,for the continuous rigorous vehicle exhaust emission standard pushes forward.The main types of NOx sensor include semiconductor oxide type,diode bridge type,optical fibre,solid-state electrolyte type,ect.The NOx sensor based on solid electrolyte has many advantages,such as high response sensitivity,high mechanical properties,corrosion-resistant,as well as matchs great to automotive vehicle system and can realize fast detection with reliable response.Conventional fluorite-phase Y2O3 stable ZrO2(YSZ)used for electrolyte of NOx sensor requires higher operating temperature to obtain desirable oxygen ion conductivity.Perovskite-type oxide shows potential application as solid state electrolyte of NOx sensor,owing to its pretty high ionic conductivity in low-medium temperature and stable performance.In this work,perovskite-phase Na0.5Bi0.5TiO3(NBT)and doping sample which were prepared by citrate sol-gel method were chosen as the solid electrolyte to fabricate a novel highly sensitive NO2 sensor with CuO as the sensing electrode and Pt as reference electrode.The results were obtained as follows:(1)Doping Na in A site of ABO3 has greatly improved the performance of sensors base on Na0.5+xBi0.5TiO3-?(x=-0.01-0.04)electrolyte.The ?(current)was almost linear to V(voltage)in the range of 0-500 ppm NO2 at 400-600?.The fitting result shows a superb linear relationship between ?? and NO2 concentrations at 450-600 ? towards 50-500 ppm NO2· The good liner fitting result of ?? values and operating temperature also exist at 475-575 ? towards 500 ppm NO2.The optimal sensor based on Na0.51 Bi0.5TiO3-? exhibited good response-recovery characteristics to NO2 and the response current values were almost linear to NO2 concentrations in the range of 50-500 ppm at 400-600 ?.The response current value towards NO2 reached maximum 11.23 ?A at 575 ?,which is higher than that of sensor based on YSZ electrolyte.The maximum sensitivity of Na0.51Bi0.5TiO3-? based sensor was 18.44 nA/ppm when exposed 500 ppm N02 at 575 ?.The possible coexistence gases(CH4,C2H4,C3H6,C3H8,CO,O2)affect little to the ?? of sensor to NO2.AI of sensor responded to NO2 was 18 higher than the sensor responded to coexistence gas.AI changed less than 3%when O2 varied from 2 to 20 vol.%at 575?.The long-term stability was also relatively good with slight decrease of 4.9%of original ?? values after 2 months.(2)Modification by doping Cu in B site of ABO3 are also beneficial to amelioration of the performance of sensors base on Na0.5Bi0.5Ti1-yCuyO3-?(y=0-0.20)electrolyte.The ?(current)was almost linear to V(voltage)in the range of 0-500 ppm NO2 at 450-600?.The fitting result shows a superb linear relationship between ??and NO2 concentrations at 450-600 ? towards 50-500 ppm NO2.The preferable sensor is the sensor based on Na0.5Bi0.5Ti0.85Cu0.15O3-? which exhibited good response-recovery characteristics to NO2,and the sensor shows better response value and response speed than the sensor based on YSZ in the same condition.The response current value of sensor based on Na0.5Bi0.5Ti1-yCuyO3-? towards NO2 reached maximum 12.25 ?A at 575 ?,which is higher than that of sensor based on YSZ electrolyte.Meantime,the response current values of the sensor based on Na0.5Bi0.5Ti0.85Cu0.15O3-? towards 50-500 ppm NO2 were almost linear at 450-600 ?.The maximum sensitivity of Na0.51Bi0.5TiO3-? based sensor reached 24.39 nA/ppm when it was exposed to 500 ppm NO2 at 500 ?.The possible coexistence gases(CH4,C2H4,C3H6,C3H8,CO,O2)affect little to the ?? of sensor to NO2·?? of sensor responded to NO2 was 13 higher than the sensor responded to coexistence gas.??changed less than 2%when O2 varied from 2 to 20 vol.%at 500 ?.The long-term stability was also good with decrease of 11.1%of original ?? values within 1.5 months which is acceptable.The performance of sensor based on non-rare-earth NBT electrolyte exhibited the better-off application prospect with low cost in motor vehicles or industrial emission processes at low-medium temperature.