| On-line monitoring of gas concentrations in the combustion process of fossil fuels,exhaust emissions,and flue gas treatment processes is the key to improving energy efficiency and reducing toxic emissions.That requires gas sensors to be able to operation in harsh environments what high temperatures,high pressures,harsh environments,exhaust speed fast,etc.The solid electrolyte electrochemical gas sensor has the advantages of high sensitivity,easy miniaturization,solid structure,and a wide range of measured gas concentration and it is the most promising sensor type suitable for high temperature and harsh environments.Around solid electrolytes suitable for high-temperature gas sensors,new types of oxygen ion conductors and proton conductors were designed and prepared.Oxygen ion conductor lanthanum silicate La10?SiO4?6O3 doped with Si site was prepared by hightemperature solid-phase synthesis method using oxides as the raw material.The results show that the conductivity of La10Si5CrO26.65 at 800 ? is 1.27×10-2 S·cm-1,and the activation energy is the smallest.Through the simulation calculation of tolerance factor and energy band structure,Hf was selected as the doping element,and Ba Zr0.8Y0.2O3?BZY?and Ba Zr0.6Hf0.2Y0.2O3-??BZHY?were prepared by the double sintering aid method,which improved sintering performance and improved electrical conductivity.Adding double sintering aid of 4 mol% Li: Zn=1: 1,the density of Ba Zr0.6Hf0.2Y0.2O3-? proton conductor sintered at 1400 ? for 8 h is high which reaches 95.64% and the grain boundary resistance is small.The conductivity of BZHY at 700 °C is 8.84?10-3 S?cm-1.Through the efficient three-phase reaction interface design,the gas sensing performance,reproducibility,stability and anti-interference ability of the sensor are significantly improved.Using oxygen ion conductors LSCO,YSZ and proton conductor BZHY as solid electrolytes respectively,the double layer structure of electrolyte dense layer/porous layer was constructed by screen printing technology.Through alternation of slurry composition,control the number of printing layer and change of sintering propess,a porous layer with adjustable membrane thickness,pore size,and porosity can be obtained.Three methods are mainly used to prepare sensing electrodes: First,the electrolyte porous layer-thick film type gas sensor was constructed on the porous layer by screen printing method.Cu Cr2O4-Cu O is used as a sensing material to prepare a mixed potential type NO2 sensor.The response signal has a good linear relationship within the NO2 concentration of 25-300 ppm at 600-700 ?,and exhibits the best sensitivity,reproducibility and stability at 600 ?.The polarization curve and AC impedance results indicate that the sensor follows mixed potential mechanism.Second,the electrolyte porous electrolyte layer/nano sensing material gas sensor is constructed by chemically impregnating the sensing material in the porous layer.Current-type NO2 sensors were prepared with Cr2O3,La Cr O3,La0.8Sr0.2Fe0.8Cu0.2O3-??LSFC?sensitive materials respectively;The limit current type O)2 sensor was prepared with a perovskite composite oxide La0.85Sr0.15 Mn O3?LSMO?sensing electrode.The mixed potential type and resistance type hydrogen sensors were prepared with Zn O sensing electrodes.The prepared series of high-temperature gas sensors have a good linear relationship between the response signal value and the gas concentration to be measured within a certain range.For the NO2 sensor,the response current of the LSFC sensor is the largest,the absolute value reaches the m A level,the sensitivity of NO2 in the concentration range of 10-200 ppm reaches 6.08 ?A/ppm.However,H2 interferes greatly on the response signal of LSFC sensor with an offset of 6.69%.Using YSZ as solid electrolyte and LSMO film as diffusion layer,a limiting current oxygen sensor was prepared.When the immersion amount is 60 ?L and polarization voltage is 800 m V,the sensing performance of the sensor sintered at 1250 ? is optimized and exhibits a good linearity between the response signal and the oxygen concentration in the range of 0 to 10000 ppm with the correlation coefficient as 0.99.The sensitivity of LSMO SE is largest at 750 ? with 2.6×10-3 m A·ppm-1.The Zn O hydrogen sensor with proton conductor BZHY as a solid electrolyte is suitable for ultra-low concentration gas detection with the H2 concentration range is 1-15 ppm.Meantime,sensitivity of the sensor increases with the increasing of operating temperature which reached a largest value of 27.0 m V/dec.at 450 ?.Third,impregnating the sensing material precursor in the porous layer and obtaining the nano metal particle composite sensing material by electrochemical exsolution method to strengthen the surface catalytic activity and further improve the gas sensing performance of the sensor.After impregnation Ag Nb O3?ANO?in the porous layer,Ag/ANO is formed by electrochemical exsolution to produce a mixed-potential NH3 sensor.The electric exsolution conditions were applied voltage of 2 V,treatment at 400 ? for 200 s,and Ag particles with a particle size of about 15 nm were obtained on the ANO substrate.At 400 ?,the sensitivity of NH3 concentration in the range of 10-400 ppm reached-80.2 m V/dec.and the sensor has good anti-interference ability for NO2.Based on the basic response data of multiple sensors,comprehensively using electrochemical impedance spectroscopy and electrochemical impedance spectroscopy differential analysis-Distribution of Relaxation Times?DRT method?,kinetic equation fitting,feature parameter extraction and phase space full parameter analysis method,etc.,systematically research the sensing process and sensing mechanism of NO2,O2,NH3,and H2 sensors,and the response mode and dynamic model of high-temperature NO2 gas sensors are proposed and verified in the research of O2,NH3,and H2 sensors.The results show that this method has a certain general adaptability.Figure 119;Table 21;Reference 201... |
PDF Full Text Request