Research And Application Of Mixed Potential Type Acetone Sensor Based On Ce_0.8Gd_0.2O_1.95

In the fields of medical diagnosis,automobile exhaust monitoring,and environmental detection,acetone sensors with high performance have gradually became critical components that are urgently needed.In terms of medical diagnosis,acetone is used as an expiration marker for diabetic ketoacidosis.The concentration in the breath of healthy people is 0.3-0.9 ppm,and in the exhalation of ketosis patients is higher than 1.8 ppm.Detection of acetone concentration enables rapid pre-diagnosis of diabetic ketoacidosis.In the field of automobile exhaust monitoring,it is reported that automobile exhaust contains a certain amount of acetone,but its concentration is not yet clear,and with the increase of human living environment requirements,the detection and control of acetone in automobile exhaust is essential.At the same time,due to the harsh detection conditions in this field,a highly stable acetone sensor is required.In the field of environmental testing,acetone is a widely used organic solvent,but because it is volatile and high concentrations of acetone vapor can cause great harm to human body,the detection of acetone is very necessary.According to relevant regulations for occupational exposure limits,the basic conditions for acetone sensors in atmosphere and industrial environments are that the lower detection limit should in sub-ppm range and the upper limit should be higher than 1000 ppm.Compared with other types of acetone sensors,mixed potential acetone sensor has the significant advantages of high reliability,good selectivity,excellent chemical stability and thermal stability,and can better meet the needs of acetone gas detection in the above three fields.In this thesis,a series of mixed potential acetone sensors based on Ce_0.8Gd_0.2O_1.95?GDC?solid electrolyte and a variety of high-performance sensing materials were developed.The sensitivity of the sensors was improved by changing the composition and modify the sensing material,and the sensor's sensing mechanism was studied.At the same time,the application bottlenecks that limit the mixed potential sensor,such as low sensitivity,narrow detection range,and insufficient stability,have been solved,and the preliminary application of the GDC-based mixed potential acetone gas sensor in medical diagnosis,automotive exhaust monitoring,and environmental detection has been achieved.The main research contents include:1.A series of MFeO₃ sensing electrode materials with perovskite structure?ABO₃?have been developed.The difference in micro-morphology of the sensing electrode material and the electrochemical catalytic activity to acetone can be changed by the difference of A-site elements,thereby improving the sensing performance of GDC-based mixed potential acetone sensors.1)Three kinds of perovskite sensing electrode materials,LaFeO₃,SmFeO₃,and BiFeO₃,were prepared by the sol-gel method.The effects of A-site element types?La,Sm and Bi?on the performance of GDC-based mixed potential acetone sensors were studied.Because of the porous microstructure and the best electrochemical catalytic activity to acetone,BiFeO₃ sintered at 800°C was the best material for preparing GDC-based mixed potential acetone sensors.The sensor based on BiFeO₃ have the sensitivity of-7 and-75 mV/decade to 1-5 ppm and 5-200 ppm acetone,respectively.The sensor also has good repeatability,humidity stability and long-term stability.2)In order to improve the sensitivity of GDC-based mixed potential acetone sensors based on BiFeO₃ sensing electrode materials towards low concentration acetone,the A site of BiFeO₃ materials was partially substituted with the same-valent element?La?.The changes in the microstructure of the electrode material and its effect on the electrochemical catalytic activity of sensing materials towards acetone after La partially replacing Bi was studied.When the amount of La substitution was50 mol%,the sensitivity of GDC-based acetone sensor prepared with Bi_0.5La_0.5FeO₃sintered at 800°C was-17.5 mV/decade towards 1-5 ppm acetone,which was 2.5times than that of the sensor based on BiFeO₃ sensing material.Therefore,it promoted the application process of GDC-based mixed potential acetone sensor in the field of breath detection.3)In order to further reduce the lower detection limit of the sensor to meet the needs of breath detection,Sr²⁺with a valence different from Bi³⁺was used to partially replace the A site of the BiFeO₃ sensing electrode material.The cathodic reaction of oxygen could be more violent,and the electrochemical catalytic activity of BiFeO₃ to acetone was increased,which further improved the sensing performance of the sensor.The effect of the substitution amount of Sr²⁺on the sensor performance was studied.Results showed that the sensor has the best sensing performance when the substitution amount of Sr²⁺was 0.6 mol%,and the detection limit of the sensor reached 0.3 ppm at590°C,which was lower than that with BiFeO₃ and Bi_0.5La_0.5FeO₃ sensing electrode material.The lower limit of detection of sensing material can reach the acetone concentration in the breath of healthy people.At the same time,the sensor has good repeatability and long-term stability.2.In order to develop a GDC-based mixed potential acetone sensor with higher sensing performance and expand the application field of the sensor,this article first combined double perovskite materials with GDC to develop high performance GDC-based mixed potential acetone sensors.1)Three sensing materials Sr₂MMoO₆?M:Fe,Mg,Ni?were prepared by sol-gel method.The effect of different B-site element on the sensing performance was studied.Related results showed that the sensitivity of the sensor with Sr₂FeMoO₆ as sensing electrode material was much higher than that of the sensors with perovskite type sensing materials.Its response value to-100 ppm acetone was-147 mV,the response time was 13 s,and the sensitivity was-100 mV/decade?5-200 ppm?.This sensor has the highest sensitivity among the reported mixed potential acetone sensors.The minimum detection limit of the sensor was 0.5 ppm,and it also has excellent repeatability.2)For the detection of high-concentration acetone gas,La₂MMnO₆?M:Co and Cu?double perovskite sensing materials were synthesized.The influence of different B-site elements on the performance of the sensing materials was studied.Results showed that La₂CuMnO₆ was more suitable as the sensing electrode material for GDC-based mixed potential acetone sensors.The sensors based on La₂CuMnO₆ has good response to acetone in the range of 10-1000 ppm,and there was a good linear relationship between the response value of the sensor and the logarithm of acetone concentration.The sensitivity was-49.3 mV/decade.Response time to 50 ppm and500 ppm acetone was 13 s and 3 s,respectively,and the recovery time was 13 s.Compared with the previous sensors,this sensor has a higher detection limit,which can be used for the detection of high-concentration acetone,and has a good application prospect in the field of forming a large-range sensor array.3.GDC-based mixed-potential acetone sensors in this work have been applied in medical diagnosis and automobile exhaust gas detection,and we also proposed related application schemes for the detection of acetone concentration in the atmosphere and industrial microenvironment.1)The sensor developed in this experiment can accurately detect the acetone concentration in the breath,which can identify ketosis patients,and according to the test results,there was a linear relationship between acetone concentration in the breath of ketosis patient and their blood ketone concentrations,which can realize the pre-diagnosis of diabetic ketoacidosis.2)A mixed potential acetone sensor based on GDC can give an immediate response to automobile exhaust.The test results on the cycle conditions of four different vehicles using different oil products showed that the change of acetone gas concentration was little to the same vehicle using different oils.However,acetone concentrations in the exhaust of different vehicle were more obvious,and acetone emission were the lowest for China V standard gasoline vehicle and China V standard diesel vehicle,indicating that the sensor developed in this paper has certain application prospects in automotive exhaust detection.3)The overall detection range of GDC-based mixed potential acetone sensor using two kinds of double perovskite materials Sr₂FeMoO₆ and La₂CuMnO₆ was0.5-1000 ppm,which can cover the entire acetone concentration range in the atmosphere and industrial microenvironment.The sensors were integrated to build a sensor array that enables the detection of acetone in the atmosphere and industrial microenvironment.In this paper,through the development of five types of perovskite and double perovskite high-performance sensing materials,and the using of a series of characterization and testing methods,the sensing mechanism of the sensor has been clarified.Five types of mixed potential acetone sensors with good application prospects such as medical diagnosis,monitoring automotive exhaust,atmospheric and microenvironment detection were developed successfully.