Solid State Electrochemical Gas Sensors Based On Stabilized Zirconia And Composite Oxide Sensing Electrodes

Gas sensor is the device or equipment that converts gas concentration into highly measurable signal.It has important application in environmental monitoring,resource detection,safety monitoring,medical diagnosis and treatment et al.In this thesis,we focus on solid state electrochemical gas sensors based on stabilized zirconia and composite oxide sensing electrodes and systematically investigate the high temperature NO_x and NH₃ sensors for vehicle exhaust monitoring,the gas sensor for lower concentration SO₂ detection in atmosphere environment,the highly sensitive acetone and ethanol sensor for volatile organic compounds?VOCs?detection from the design and preparation of sensing electrode materials.The sensing mechanism involved in the mixed potential is verified by measuring the polarization curves.By mixing composite oxide sensing electrode materials and YSZ particles,the area of three phase boundary?TPB?is increased and the sensitivity of fabricated sensor is enhanced.The main contents of the thesis are as following:?1?For real-time online monitoring NH₃ concentration in vehicle?mainly diesel and direct injection gasoline vehicles?exhaust,a new Ni₃V₂O₈ composite oxide sensing electrode material was prepared via facile sol-gel method and used for fabricating the mixed potential type stabilized zirconia based NH₃ sensor.The influence of regulating sensing electrode microstructure by changing sintering temperature?800,1000 and 1200°C?on sensing characteristics was investigated and results showed that the sensor attached with Ni₃V₂O₈ sensing electrode?SE?sintered at 1000°C exhibited the largest sensitivity?-96 mV/decade?to 50–500ppm NH₃ at 650°C.The good sensing performance is attributed to loose and porous sensing electrode structure and the excellent electrochemical catalytic activity to NH₃.?2?In order to purify NO_x in vehicle exhaust,the real-time accurate measurement of gas concentration was desired.The high performance on-board YSZ-based mixed potential type NO₂ sensors were developed in terms of design of new sensing electrode materials and fabrication of high performance three phase boundary?TPB?.I.New MNb₂O₆?M: Co,Zn and Ni?columbite type composite oxide sensing electrode materials were synthesized and used for investigating NO₂ sensing performance.The sensor using CoNb₂O₆-SE displayed the highest response value to NO₂ at 750°C.The response of present device to 100 ppm NO₂ was 99 mV.The sensor also displayed good selectivity,water-resistance and stability.II.The response of the sensor?S0?using Co₃V₂O₈ sensing electrode to 100 ppm NO₂ at 700°C was 67 mV.The response value of the sensor was enhanced when the Co3V2O8 sensing electrode was mixed uniformly with YSZ particles and optimal additive amount was 40 wt.%YSZ.The response value of sensor?S40?attached with Co₃V₂O₈?+40wt.%YSZ?-SE to 100 ppm NO₂ increased by 63 mV comparing with S0.The reason for improving the sensing performance is as follows: Due to the addition of YSZ particles,a good contect with the sensing electrode material and solid state electrolyte was formed and the area of TPB was effectively improved,in this case,the number of electrochemical reaction active site was increased and electrochemical reaction was promoted.?3?In view of the low concentration SO₂ detection requirement in the atmospheric environment,the SO₂ sensor based on YSZ and columbite type MnNb₂O₆ composite oxide sensing electrode was investigated and the sensing characteristic was optimized by changing the calcination temperature?800,1000 and 1200°C?of composite material.The sensor attached with MnNb₂O₆ sensing electrode calcinated at 1000°C showed the highest response value to SO₂ and the low detection limit of 50 ppb at 700°C.We explained the selectivity by investigating the complex impedance in different types of gases.?4?In order to solve the acetone detection problem in the area of atmosphere and microenvironment,firstly,YSZ-based mixed potential type acetone sensors using M₃V₂O₈?M: Zn,Ni and Co?sensing electrodes were developed and the effect of sensing electrode on sensing performance was investigated.Results showed that the sensor attached with Zn₃V₂O₈-SE exhibited the highest response to acetone and the response value to 100 ppm acetone was-69 mV,and the low detection limit of 1ppm at 600°C.Secondly,to gain the acetone sensor with the higher sensing performance,the high performance YSZ-based acetone sensor using NiNb₂O₆ sensing electrode was fabricated and the sensing characteristic was optimized by changing the calcination temperature?800,1000 and 1200°C?of sensing electrode material.The sensor attached with NiNb₂O₆ sensing electrode calcinated at 1000°C showed the highest response value?-113 mV?to acetone and the low detection limit of 500 ppb at 650°C.Finally,for exhale markers detection of diabetic patients,the columbite type MNb₂O₆?M: Cd,Co,Zn,Mn and Ni?composite oxide sensing electrode materials were designed and prepared.Results showed that the sensor attached with CdNb₂O₆ sensing electrode displayed the highest response to acetone and the low detection limit of 200 ppb.?5?In view of the low concentration ethanol detection requirement,the highly sensitive YSZ-based ethanol sensors utilizing MNb₂O₆?M: Zn,Ni and Co?sensing electrodes were fabricated and the sensing characteristics were enhanced by choosing the suitable sensing electrode and optimizing the calcination temperature?800,1000 and 1200°C?.Results showed that the sensor attached with Zn Nb₂O₆ sintered at 1000°C exhibited the highest respose value and the sensitivity to 5–200ppm ethanol at 625°C was as large as-112 mV/decade.Additionally,the sensor also displayed good repeatability,stability and acceptable selectivity.