Preparation Of Nano-sized In₂O₃ Material And Research On Ammonia Sensing Performance

NOx in vehicle exhaust can cause serious environment pollution,and Selective Catalytic Reduction(SCR)could reduce NOx by injecting urea which then decomposes to NH₃.However,the“Ammonia Leakage”caused by excessive urea injection has also serious consequences,so it is necessary to install suitable sensors downstream of SCR to detect NH₃ concentration.Among various types of sensors,the mixed potential type sensors have broad application prospects because of simple structure,good adaptability and excellent sensitive property.Therefore,it is of great significance to study the morphology of the sensing materials and the structure of the ammonia sensor to improve its sensing performance of detecting NH₃.In this paper,the self-propagating high-temperature combustion synthesis method(SHS)was used to synthesize nano-In₂O₃ ammonia-sensitive material.The NH₃ sensing characteristics of nano-In₂O₃ were studied.The effects of sensing electrode parameters and preparation processes on the sensing performance were investigated.The main research work of this paper is as follows:Firstly,the optimal operating temperature of the ammonia sensor with In₂O₃ sensing electrode was determined by experiments as 550?.The further experiments found that the sensing electrode thickness was104.20?m which calcinated at 900?had the best ammonia sensing performance,and the sensitivity was-64.20 m V/decade.Secondly,the relationship between the morphology of sensing electrode and ammonia sensing performance was investigated by doping YSZ or graphite with different proportions before calcination.It was found that the introduction of YSZ did not improve the sensitivity,while it could significantly increase the response potential.Characterizations manifest that inhibition towards the growth of In₂O₃ grains was gradually enhanced with the increasing of YSZ content.The In₂O₃ ammonia sensor doped with30%YSZ(mole fraction)whose sensitivity was-61.25 m V/decade,which had the most excellent response potential value to NH₃ among various samples.When this sample exposed to 10ppm NH₃,the potential value is-100.46m V,which was 1.64 times higher than the result of undoped YSZ sensor.In contrast,the response potential and sensitivity of the In₂O₃ammonia sensors doped different graphite contents were not as good as expected,which indicating that too many pores existing in the In₂O₃ sensing electrode was not conducive to the detection of NH₃.In this paper,the sensing performance of In₂O₃ ammonia sensor doped with 30%YSZ against various interfering gases were further studied,and it was hard to neglect the interference of CO and NO₂.In order to improve the selectivity of the sensor to NH₃,Ag was introduced on the In₂O₃ layer from the perspective of the sensing electrode.The approach not only improved the sensitivity to-68.20 m V/decade,but also obviously inhibited the interference of CO and weaken the influence of NO₂ to some extent.Secondly,from the perspective of reference electrode,the mixture of Cu O and Fe₂O₃ in different proportions was selected as reference electrode.It was found that utilizing metal oxide as reference electrode could more effectively reduce the interference of NO₂.