Preparation Of Pd Clusters Decorated SnO₂-based Nanofibers And Its Hydrogen Sensitivity Improvement Mechanism

The online monitoring of dissolved characteristic gases is an important technical means on realizing oil-immersed electrical equipment condition-based maintenance.H₂is a key characteristic parameter that reflects the spark,arc and partial discharge faults in oil-immersed electrical equipment.Gas sensors have become the key to gas analysis due to their fast response and mature technology.It is of great significance to the health assessment and safe operation of power equipment.The SnO₂ semiconductor gas sensor have been widely studied in the field of dissolved gas detection due to the advantages of simple preparation and environmental friendliness.However,the pure SnO₂gas sensor still has the problems of low sensitivity and high working temperature,which greatly limits its further promotion and application.Studies have shown that the preparation of composite SnO₂-based gas-sensing materials with large specific surface area and high porosity by appropriate processes is an important way to improve their gas-sensing performance.In this paper,the Pd clusters decorated SnO₂-based mesoporous nanofibers were synthesized via electrospinning method along with magnetron sputtering,and the gas-sensing properties of the SnO₂-based sensors to H₂ were tested.The first principles calculations were used to analyze the micro-electronic properties of Pd clusters modified SnO₂ models and its adsorption models of H₂.The thesis combines experimental testing and simulation analysis to study the gas-sensing performance improvement mechanism of Pd clusters surface decorated SnO₂ gas sensor.The main research contents and conclusions are as follows:(1)In the aspect of material preparation,electrospinning technology combined with magnetron sputtering is used to prepare the Pd clusters decorated SnO₂-based nano gas-sensing materials.The successful preparation of SnO₂ nanofibers and Pd clusters surface modified SnO₂ materials was proved by various characterization methods.The specific surface areas of the intrinsic and Pd clusters decorated SnO₂ gas-sensing materials are47.427 m²/g and 139.214 m²/g,respectively.(2)In the aspect of gas-sensing performance testing,the intrinsic and Pd clusters decorated SnO₂ gas sensors were prepared by the traditional side heating process,and their gas-sensing characteristics of H₂ were tested.The results show that the optimal working temperature of the Pd clusters-decorated SnO₂ gas sensor is 25?lower than that of the intrinsic SnO₂ sensor;the Pd clusters-modified SnO₂ gas sensor has a higher sensitivity of 27.996 to 100 ppm H₂ at the optimum operating temperature;both sensors show excellent dynamic repeatability in six test cycles,while the response and recovery time of Pd clusters-modified SnO₂ sensor are shortened by 15 s and 10 s,respectively.(3)In the aspect of gas-sensing performance improvement mechanism,the intrinsic SnO₂,Pd _N(N=2-6)clusters,Pd _N clusters-modified SnO₂ and H₂ gas adsorption models were established based on the first-principles calculations.The simulation results indicate that the structure of the SnO₂ crystal model modified by Pd₅ clusters is the most stable among all the composite models of Pd _N clusters;Compared with the pure SnO₂,the Pd₅-SnO₂ composite has shorter adsorption distance,greater charge transfer capacity,larger gap change and stronger adsorption effect on H₂.(4)The comprehensive simulation and experimental analysis show that the modification of Pd clusters reduces the work function of the material and makes the adsorption reaction with H₂ more intense.On the other hand,it increases the specific surface area and oxygen defect content of the gas sensing material,and finally improves the gas sensing performance of pure SnO₂.In addition,we used the sensitivity formula to predict the sensitivity of the sensor,and the correlation results show the same rule as the experimental test.In this paper,by adjusting the microstructure and surface characteristics of gas-sensing materials and based on the micro electronic parameters of the gas adsorption model,the idea of developing high-performance H₂ sensor is provided.