Research On Solid Electrolyte Material Of GdAlO₃-based Applied To NO_x Sensor

States increasingly stringent of auto exhaust emission standard,prompting a market demand for vehicle NO_x sensor.The electrochemical type NO_x sensor based on solid electrolyte is easy to cooperating with components of the EFI system,and it receives widespread attention because it can be implemented on-site inspection and effectively reduce exhaust emissions of NO_x.Up till now,NO_x sensors based on YSZ were the most widely used,which sensor exhibits a high potential response and response/recovery time quickly.However,due to the intrinsic limitation in electrochemical properties of YSZ,such sensor can only suitable for working above 800?.Therefore,it's extremely urgent to exploita a new medium-temperature oxygen ion conductor material which as a solid electrolyte using for sensor instead of YSZ.Based on the above situation,in this paper we concentrate on an amperometric-type or impedancemetric type NO₂ sensor was fabricated selection of perovskite-type oxide Gd1-xCaxAlO_3-??referred to GCA,x=0-0.2?as solid electrolyte material,and the sensor sensitivity,selectivity and stability et al.were studied and analyzed,respectively.The main contents are as follows:?1?The Ca-doped GdAlO3 powder was prepared through a citrate gel route,and the powder characterized by XRD,TG-DSC and FTIR.Moreover,the linear shrinkage,impedance spectroscopy etc.of the solid electrolyte material were investigated,and the electrochemical characterization of GCA materials were studied and analyzed;?2?A series of NO₂ sensor samples were fabricated using NiO as sensing electrode,Pt as reference electrode and perovskite-type oxide Gd1-xCaxAlO_3-? as electrolyte,and comparative sensitivity characteristics of series sensor samples;?3?An impedancemetric type NO₂ sensor based on Gd_0.85Ca0.15AlO_3-??GCA-15?was fabricated,and the sensing characteristics and stability of sensor were studied;?4?With the purpose of improving the properties of the sensor,an amperometric-type NO₂ sensor with GCA-15 solid electrolyte and using GCA-15 doping NiO as sensing electrode was fabricated,and its sensitivity characteristics were evaluated.The following results were made:?1?The Gd_0.85Ca0.15AlO_3-? sample exhibited maximum conductivity of 1.96×10^-2 S/cm at 950?,and Gd0.9Ca0.1AlO_3-? sample showed the minimum activation energy of 0.95 eV;?2?The sensor exhibited good sensitivity to NO₂ at 400-500?,The sensor showed the optimum sensitivity at 500?.The sensor based on Gd_0.85Ca0.15AlO33-?substrate gives the highest NO₂ sensitivity of 2.88 nA/ppm,and the response current value up to 5.57 ?A at 500?.Further,a 90%response and recover time to 500 ppm NO₂ are about 119 s and 92 s at 500?,respectively.Moreover,the sensor shows excellent selectivity and stability;?3?An impedancemetric type NO₂ sensor based on GCA-15 gives the highest NO₂ sensitivity at 500?.The shortest response time of sensor is 28 s at 500?,and the maximum length is 55 s at 750?.In addition,the sensor exhibited outstanding stability;?4?The sensor using NiO?+15%GCA-15?as SE gives the largest NO₂ sensitivity and highest response current among all the samples at 400?.The largest response current value is 1.71 times the response current of sensor with NiO sensing electrode.In summary,a NO₂ sensor based on GCA-15 solid electrolyte exhibits good sensitivity,selectivity and stability for NO₂ gas,which has important significance in automobile exhaust monitoring,and it also has broad development prospect in the NO_x sensor field.