Study On Gas Sensing Properties And Mechanism Of ZnO Based Heterojunction Sensor Detecting SF₆ Decomposed Components SO₂,H₂S

Sulfur hexafluoride?SF₆?decomposition component detection is one of the effective ways to monitor early insulation failures in Gas Insulated Switchgear?GIS?equipment.Sulfur dioxide?SO₂?and hydrogen sulfide?H₂S?are the key characteristic components of SF₆ decomposition gas,which can effectively reflect the type and severity of insulation faults.Metal oxide semiconductor zinc oxide?ZnO?gas sensors have received widespread attention due to their low cost and sensitivity to multiple gases.However,pure ZnO gas sensors have limited gas-sensitive response capabilities to SO₂ and H₂S.To meet the needs of practical applications,modified and designed were to improve their gas-sensitive characteristics.In this dissertation,the ZnO-based heterojunction gas sensor and its gas sensing mechanism are studied for the SO₂ and H₂S which are the decomposition components of SF₆.First,electrospinning was used to prepare ZnO,tin dioxide?SnO₂?,copper oxide?CuO?,SnO₂-ZnO-based n-n heterojunction,and CuO-ZnO-based p-n heterojunction gas-sensitive materials.And characterize their morphology,element composition and grain structure.The inductive and planar gas sensors were made to test the gas sensitivity of SO₂ and H₂S gases.Based on the first-principles principle,a perfect crystal model of ZnO,a crystal model doped with Sn or Cu atom,and adsorption models of SO₂ and H₂S were qualitatively analyzed.The effects of the Sn and Cu incorporation on the gas-sensitive properties of ZnO were qualitatively analyzed from a micro perspective.The main research work of this paper is as follows:?1?Pure SnO₂,ZnO,SnO₂-ZnO composite nanofiber gas-sensitive materials were prepared by electrospinning,and were characterized.Based on the laboratory gas sensitivity test platform,SO₂ and H₂S gas sensitivity were tested.The results show that the SnO₂-ZnO composite nanofiber gas sensor shows higher sensitivity,lower optimal operating temperature,and faster response recovery time for testing SO₂ and H₂S gases.The gas sensor detects 50?L/L of SO₂ and H₂S gas,the best working temperature is as low as 200?,250?,the sensitivity is 35.0,62.2,and the response recovery time is 22-34s,18-32s.At the same time,the SnO₂-ZnO gas sensor has better linearity and stability when testing both gases.?2?The pure CuO,ZnO,CuO-ZnO nanofiber gas sensing materials were prepared by electrospinning method,and the microstructure characterization analysis was carried out,and the gas sensing characteristics of SO₂ and H₂S gas were tested.The results show that the CuO-ZnO-based p-n heterojunction gas sensor for H₂S gas sensing performance is significantly better than pure ZnO and CuO gas sensors,with higher sensitivity,lower operating temperature and better stability.Under the optimal working temperature of200?,the sensitivity of detecting 50?L/L H₂S gas is as high as 83.3.At the same time,the element can effectively detect 0.5?L/L H₂S gas,and the minimum detection concentration meets the actual needs.?3?Based on the first principle of density functional theory,the Sn and Cu substitution Zn site doping model and the SO₂ and H₂S gas adsorption model were established,and the adsorption structure,adsorption energy,charge transfer amount,charge distribution and molecular orbital adsorption were calculated in detail parameters.Comparing experimental phenomena and theoretical calculation results:Sn or Cu-doped ZnO reduces the adsorption barrier of intrinsic ZnO to gas molecules,making gas molecules more easily adsorbed on the crystal surface.The adsorption capacities of the three adsorption substrates for SO₂ gas are:Sn-ZnO>Cu-ZnO>ZnO,and Cu-ZnO>Sn-ZnO>ZnO for H₂S gas.Among them,the adsorption energy of Cu-ZnO?0001?crystal surface adsorbing H₂S gas is the largest,it is-2.2152eV,the charge transfer amount is0.322e,the macroscopic performance is that the CuO-Zn O gas sensor detects H₂S gas,the surface resistance change increases,and the sensitivity is significantly improved.The calculated results are in agreement with the experimental results,which verifies that the method based on first-principles calculation and interpretation of the gas sensing mechanism of the ZnO-based heterojunction gas sensor has good feasibility and accuracy,and provides a theory for the development of high-performance ZnO gas sensors guide.