Research On Hydrogen Sulfide Gas Sensor Based On Nickel Oxide

H₂S is a colorless,flammable,highly toxic acidic gas,and long-term exposure to low concentrations of H₂S would cause damage to human vision,respiration,and the central nervous system.In recent years,oxide semiconductor gas sensors have made some progress in the detection of H₂S.However,there are still face some problems such as high operating temperature,long recovery time,or even inability to recover,which are not conducive to the practical application of the sensor.The performance of the sensors needs to be further improved.Nickel oxide(NiO)as a typical p-type semiconductor material,has excellent catalytic activity,stable electrical and chemical properties,and moderate resistance in air,has been reported to be used for the detection of H₂S gas.In this thesis,using NiO as the base sensing material,a series of planar-type H₂S gas sensors with low operating temperature(100-155°C),high selectivity,and fast response recovery characteristics were prepared by both planar transfer processes to construct thick nanofiber films and electrochemical deposition to grow sensitive films in situ.The main research includes:1.The NiO nanofibers sensing layers were prepared by electrospinning technique and planar transfer process,and the effects of precious metal Pd and Pt modifications on the phase structure,morphological structure,and elemental composition of NiO gas sensing materials were systematically investigated.The gas sensing test results showed that when Pd was used as the catalyst,the 2 wt%Pd-modified NiO nanofibers exhibited the best gas sensing properties at 115°C with a response value of 43.6 to 10 ppm H₂S gas,response recovery times of 146 s and 28 s,respectively,and a lower detection limit of 200 ppb.When Pt was used as the catalyst,the 0.5 wt%Pt/NiO nanofibers showed a response value of 53.4 for 10 ppm H₂S gas at 100°C with a lower detection limit of 100 ppb.Pt as a catalyst requires a smaller dose compared with Pd and the sensor with Pt modification achieved higher sensitivity and lower detection limit at a lower temperature.The better gas sensing response obtained with Pt modification can be attributed to the better catalytic activity and smaller particle size of the Pt than Pd O.2.The thick film H₂S sensors have low operating temperature and lower detection limit,but the response recovery characteristics need to be further improved.Considering that the thin film material is more conducive to the rapid adsorption and desorption of gas,which can enhance the response recovery speed of the sensor,we have used the electrochemical deposition method to achieve the in-situ growth of NiO thin films on the non-conductive ceramic substrates by regulating the electrochemical deposition voltage and time,and after proper pretreatment of the substrate.The resulting films have a thickness of about 1.8?m and are porous,which facilitates the rapid diffusion and response of the gas.3.The Porous NiO sensing thin films modified with noble metal Pd or Pt and base metal Cu were prepared by electrochemical deposition technique to obtain the planar thin film H₂S gas sensors with low detection limit and fast response recovery characteristics.Among them,the 0.5 wt%Pt/NiO film showed a response value of 76.6 for 10 ppm H₂S at the optimal operating temperature of 140°C with a recovery time of 26 s.The 2 wt%Pd-modified NiO film showed a response value of 515.3 for 10 ppm H₂S at an optimal operating temperature of155°C with a recovery time of only 7 s.The Ni:Cu molar ratio of 9:1 thin film showed a lower limit of detection of H₂S down to 100 ppb at 140°C with a recovery time of 16 s.The H₂S sensors with fast recovery characteristics were obtained by thin filming of NiO sensitive materials and catalyst modification.In this thesis,a stepwise improvement in the performance of NiO-based H₂S gas sensors is achieved in terms of dopant concentration,device structure,and experimental techniques.Compared with existing work,the sensors prepared in this thesis achieve rapid detection and fast recovery of H₂S gas at lower temperatures,with good selectivity and stability.The prepared thick film sensors have a simple preparation process,which is conducive to mass production and has a lower operating temperature and lower detection limit for H₂S gas;while the thin film sensors have better consistency and controllability,easy integration,higher sensitivity,and faster response recovery characteristics for H₂S gas,and has great potential for application in the field of low concentration H₂S detection.