Solid Electrolyte Gas Sensors Based On Stabilized Zirconia And Ti-based Composite Oxide Sensing Electrodes

Solid electrolyte gas sensors have important applications in pollution source monitoring,atmospheric/microenvironment monitoring,industrial/home safety,resource detection,medical diagnosis and treatment,aerospace and other fields,and are an important frontier in the field of sensors.New solid electrolyte sensors based on the principle of mixed potential have outstanding characteristics of good selectivity,fast response recovery and high stability.Especially,with the development of excellent oxide sensing electrodes,the types of detectible gases are constantly expanding,and the application fields are constantly expanding.This thesis focuses on the urgent need for high-performance gas sensors in the fields of mobile pollution source monitoring,atmospheric/microenvironment/industrial safety monitoring,and medical diagnosis and treatment.To build a mixed potential solid electrolyte gas sensor based on stabilized zirconia(YSZ)and composite oxide sensing electrodes as the research goal,by designing and preparing a novel Ti-based composite oxide sensing electrode,the electrochemical catalytic activity,micro-nano structure and the microstate of the three-phase reaction interface(TPB,the interface formed by the gas to be measured,YSZ solid electrolyte and sensing electrode)of the sensing electrode were controlled,developing high-sensitivity and high-temperature NO₂ sensors for on-line monitoring of vehicle exhaust(OBD),high-sensitivity and high-selectivity SO₂ sensors for atmospheric environment monitoring,ppb-level low detection limit acetaldehyde sensors for the detection of VOCs in microenvironments,and high sensitive acetylene sensor for online monitoring of electrical insulation equipment failures and high-performance acetone sensor for non-invasive,painless and convenient diagnosis of diabetes,the specific research contents are as follows:(1)For the requirement of in-situ accurate measurement of NO_x in motor vehicle exhaust,Co Ti O₃ sensing electrode material was synthesized by sol-gel method,and a planar stable zirconia based mixed potential on-board high temperature NO₂ gas sensor was fabricated.By optimizing the operating temperature of the sensor(550-750?),the sensing characteristics are effectively improved.When the operating temperature is650?,the sensor prepared by Co Ti O₃ sensing electrode material shows the highest value to 100 ppm NO₂,which is 130 m V.At the same time,the sensor has a detection limit of 500 ppb for NO₂,good sensitivity(60 m V/decade),excellent selectivity and good stability.It can provide potential application devices for on-board nitrogen oxide sensing system.The polarization curve was used to verify the mixed potential sensing mechanism.(2)Atmospheric pollution gas(SO₂)is the main pollutant that causes acid rain,which has the characteristics of local distribution and instantaneous change.Therefore,it is necessary to develop highly sensitive and highly selective SO₂ sensors to build a node-intensive atmospheric environment monitoring Internet of Things.In this paper,we synthesized three titanate composite oxide sensing electrode materials(Zn Ti O₃,Co Ti O₃ and Ni Ti O₃),by optimizing the sensing electrode electrochemical catalytic activity,it is defined that the sensor prepared by Zn Ti O₃ sensing electrode material exhibits the highest response value to 1 ppm SO₂(-22.5 m V),with the low detection limit of 0.1 ppm,its excellent sensitive performance is mainly attributed to its good electrochemical catalytic reaction activity.In addition,the sensor also shows good selectivity and repeatability,providing core node technology for building a new urban atmospheric environment Internet of Things.(3)In response to the demand of VOCs gas detection in the atmospheric and micro-environment,YSZ-based mixed potential ppb-grade acetaldehyde sensor prepared by Ni Ti O₃ sensing electrode material was developed for the first time.By changing the sintering temperature to regulate the porosity of the sensing electrode materials and the micro-state of the three-phase interface,the internal relation between the sensitivity and the porosity and micro-state of the three-phase interface was clarified,and the optimum sintering condition of 1000?was defined,and the electrochemical impedance measurements are used to verify that the sensing electrode under the condition of 1000?sintering temperature has the highest electrocatalytic capability for acetaldehyde.On the optimal operating temperature,the low detection limit of the sensor is as low as 200ppb,and has fast response recovery characteristics to 50 ppm acetaldehyde with 10 s and 26 s,it also has good repeatability,selectivity and stability.(4)In view of the urgent need to monitor the fault condition of electrical insulation equipment,by designing/screening composite oxide sensitive electrodes(Cd Ti O₃,Ni Ti O₃ and Co Ti O₃)and optimizing the working temperature of the sensor(510-590?),a highly sensitive C₂H₂ sensor based on stable zirconia and Cd Ti O₃ sensing electrode material was developed.The results show that the sensor has the highest response value to 100 ppm C₂H₂ at 550?,the response value is-126 m V,the sensitivity to 0.5-5 ppm and 5-100 ppm C₂H₂ are-8 m V/decade and-91 m V/decade,respectively.Meanwhile,the sensor has good selectivity,repeatability and high temperature stability in the period of 30 test days.In order to explain the reasons for the good sensitivity of the sensors,the polarization curves and complex impedance electrochemical performance of the sensors were tested.(5)The gas in the breath is a specific disease biomarker,and the health condition can be monitored by detecting the expiratory biomarker.Acetone gas in exhaled breath is an expiratory biomarker of diabetes,and it has been a new method for painless,non-invasive diagnosis and monitoring of diabetics via detecting acetone.It fabricated a YSZ-solid electrolyte type acetone sensor using Fe₂Ti O₅-Ti O₂ sensing electrode material,the sensitivity and selectivity were effectively improved by compounding oxide sensing electrodes.Further optimizing the working temperature to lower the detection limit.When the optimal working temperature is 590?,response value of the sensor to 20 ppm acetone is-75 m V,and the detection limit is as low as 0.1 ppm,the sensor also has excellent moisture resistance.Breath detection was carried out of healthy volunteers and diabetic volunteers using the developed acetone sensor,it was found that the response values of the sensor to diabetic patients were much higher than those to healthy volunteers,and the sensor could effectively distinguish healthy people from diabetic patients.