Research On Solid State Electrochemical Gas Sensor Based On YSZ And New Oxide Sensing Electrode

Solid electrochemical gas sensor based on yttrium stabilized zirconia（YSZ）solid electrolyte,due to high sensitivity,good selectivity and reliable stability,has a good application prospect in environmental monitoring,medical diagnosis,automobile exhaust monitoring,smoke alarm and other fields.Therefore,high performance YSZ-based mixed potential sensors have been fabricated by the development of new sensing electrode materials,the adjustment of microstructure and the improvement of sensor structure in this paper.The sensing performance of the sensor is improved,and the sensing mechanism of the sensor is systematically and deeply studied,which solves the problem of the narrow detection range,low sensitivity,lack of stability and selectivity and other bottlenecks in some specific fields.Besides,we also explore the application potential of sensors in the field of breath analysis of diseases diagnosis,promote the industrialization development of the sensors.The detailed research is as follows:1.In order to meet the SO₂ detection requirements of atmospheric environment monitoring and industrial exhaust emission,new type oxide electrode material Zn Ga₂O₄is prepared by a hydrothermal method,and combined with Pt electrode to fabricate a YSZ-based mixed potential SO₂ gas sensor.The research shows that when measured high concentration SO₂ or after a long-term measurement,the response direction has been reversed,which seriously affects the effective detection range of the sensor.Through the EDS and XPS tests on Zn Ga₂O₄ and Pt electrodes,it is proved that a large amount of S element is deposited on the surface of Pt electrode,and Pt S with high electrochemical catalytic activity for SO₂ is generated,which increases the degree of electrochemical reaction at the Pt electrode,the mixed potential of this electrode is increased,and eventually exceeds that of Zn Ga₂O₄ electrode and the reversal of the sensor response direction is occurred.Based on the research on the response direction reversal,the sulfurization scheme was designed by using the S deposition principle,and the Pt S sensing unit with high electrochemical catalytic performance was formed on the Pt electrode.The high performance SO₂ sensor was developed,and its detection range was expanded to 0.05-500 ppm with good stability and humidity resistance.2.In order to meet the needs of diagnosing diabetes by breath analysis,a series of high-performance YSZ-based mixed potential acetone sensors have been developed.First,the sensing electrode materials AMn₂O₄（A=Co,Zn and Cd）are prepared by a sol-gel method,and the influence of element types on the electrochemical catalytic activity of the electrode material is studied.In order to improve the sensitivity of the sensor,new sensing electrode materials Co_1-xZn_xFe₂O₄（x=0,0.3,0.5,0.7 and 1）and Sm_2-xSr_xNi O₄（x=0.4,0.6 and 0.8）are successfully synthesized,which enhanced the electrochemical catalytic ability of the sensiting electrode to acetone and improved the sensitivity of the sensor.（1）The sensing electrode materials AMn₂O₄（A=Co,Zn and Cd）are prepared by a sol-gel method,and the influence of different A-site elements on the electrochemical catalytic ability of the sensing electrode is studied.Among them,the Cd Mn₂O₄electrode has the strongest electrochemical catalytic ability to acetone,and the sensor with Cd Mn₂O₄ sensing electrode has the highest response to 10 ppm acetone.The detection range of the sensor is 0.2-50 ppm,and the sensitivity to 0.2-1 ppm and 1-50ppm acetone are-8 m V/decade and-28 m V/decade,respectively.It has rapid response and recovery speed,good repeatability and stability.（2）In order to improve the sensitive of the sensor,we develop a new type of sensing electrode material Co_1-xZn_xFe₂O₄（x=0,0.3,0.5,0.7 and 1）.The effect of different ratios of Co and Zn on the electrochemical catalytic ability of the sensing electrode is emphatically studied.The results show that when the ratio of Co to Zn is1:1,that is,when the electrode material is Co_0.5Zn_0.5Fe₂O₄,the electrode material has the strongest electrochemical catalytic ability for acetone,and the sensor has the highest sensitivity to 5-100 ppm with-63 m V/decade,the response to 100 ppm acetone is as high as-130 m V,the detection range is 0.3-100 ppm.The sensor also has excellent repeatability and humidity resistance.（3）A seris of new type sensing electrode materials Sm_2-xSr_xNi O₄（x=0.4,0.6 and0.8）are designed and prepared.Sr is used to replace part of the Sm element in the Sm₂Ni O₄matrix material,and synthesized the sensing electrode material Sm_2-xSr_xNi O₄（x=0.4,0.6 And 0.8）,the material structure is stabilized and oxygen vacancies are increased,and the oxygen ion mobility of the electrode material is improved.Results have shown that sensor based on Sm_1.4Sr_0.6Ni O₄ sensing electrode has the highest response to 5 ppm acetone,and the detection limit can reach 0.3 ppm.The sensitivity of the sensor to 0.3-5 ppm and 5-100 ppm acetone is-13 m V/decade and-55 m V/decade,respectively.It has both rapid response/recovery property and excellent stability.3.In order to solve the problem that the acetone sensor is susceptible to H₂S and has insufficient selectivity,a new type of sensor with combined electrode structure is constructed by using H₂S sensing unit to counteract the effect of H₂S.Two sensing electrode materials,Ni Al Ga O₄ and Sm_1.2Sr_0.8Co O₄,are successfully synthesized by the sol-gel method.Since Ni Al Ga O₄ and Sm_1.2Sr_0.8Co O₄ have roughly the same electrochemical catalytic ability for H₂S,and the electrochemical catalytic ability of Sm_1.2Sr_0.8Co O₄ electrode for acetone is higher than that of Ni Al Ga O₄ electrode,these two materials are used as combined sensing electrode to developed a new type structure YSZ-based gas sensor.The sensor basically has no response to H₂S,but has a good sensing performance to acetone,its selectivity has been effectively improved.4.A type of new oxide sensing electrode material La₂Ni O₄ is prepared by a sol-gel method,and a high-performance YSZ-based H₂S gas sensor was fabricated,and the effect of the citric acid amount on the microstructure of the sensing material is studied.The results show that when the ratio of citric acid and metal ions is 1:1,the electrode material shows the largest pore volume.The results also show that the sensor based on this sensiting electrode has the highest response value to 0.5 ppm H₂S.The lower detection limit of the sensor reaches 0.02 ppm with good repeatability and selectivity.In order to shorten the recovery time of the sensor,a short temperature pulse with a temperature of 700°C with 60s is added during the recovery process,which shortens the recovery time from the original 20 minutes to 150s,and has no effect on the other performance of the sensor.5.The developed YSZ-based mixed potential sensors are used to measure the simulated patient exhaled breath and the exhaled breath of diabetic patients collected from the hospital,which proves that it has a good application prospect in the field of diagnosis of diseases by breath analysis.（1）The combine-sensing electrode sensor based on Ni Al Ga O₄ and Sm_1.2Sr_0.8Co O₄sensing materials has completely different sensitivity to the breath of healthy people and simulated diabetic patients,which proves that it has a good application prospect in the field of diagnosis of diabetes by breath analysis;YSZ-based gas sensor based on Ni Al Ga O₄ sensing electrode can also distinguish the breath of healthy people and simulated halitosis patients at 700°C,indicating its application ability in the diagnosis of halitosis patients.（2）The sensor based on the Sm_1.4Sr_0.6Ni O₄ sensing electrode is used to detect the acetone concentration in the exhaled breath of diabetic patients with different blood ketone concentrations.The results show that the sensor has fast response/recovery characteristics and stable response status for all collected exhaled breaths,which indicating the sensor can effectively distinguish between healthy people and diabetic.In addition,the corresponding relationship between the blood ketone concentration and the response of the sensor and the acetone concentration in exhaled breath was obtained.The diagnosis of diabetic patients with ketoacidosis is initially realized by breath analysis.