Study Of Surface State Modulation Mechanism Based On Indium Oxide Nanotube Hydrogen Sensors

Hydrogen energy has been developed and applied in aerospace,automobile and ship,metallurgy and heating,etc.It has a very broad application prospect and development potential.Hydrogen often exists in the form of hydrogen gas,which is inevitably present in the production,storage,transportation and use of hydrogen energy.Hydrogen is a flammable,explosive,colorless and odorless gas,which is difficult to detect by human sensory system alone.In order to monitor and control the presence and concentration of hydrogen more precisely and to prevent the risk of hydrogen leakage,the need for hydrogen sensors has arisen.Because metal oxide semiconductor materials have characteristics such as fast response time,low preparation cost,simple structure,long service life,easy micro-integration and easy operation,they have gradually become one of the most widely studied and applied gas sensors.Among them,indium oxide has become a popular material for gas sensing because of its good electrical conductivity,light transmission and excellent catalytic properties as well as high stability.However,as a hydrogen sensor,pure indium oxide still has challenges for high performance sensing of hydrogen,such as high operating temperature,low response,slow response recovery,not low enough detection limit,not good enough selectivity,etc.In this regard,we need to optimize the sensing performance of indium oxide based hydrogen sensors.Therefore,in this thesis,taking hydrogen detection as the basic orientation,we use a simple electrostatic spinning method to prepare indium oxide nanotube material and take it as the basic research object,and based on its advantage of specific surface area,we modify it with oxygen vacancy increase,noble metal modification and bimetallic co-modification,etc.,in order to improve the indium oxide nanotube material by increasing the adsorption sites on the surface of the material,regulating the baseline resistance of the device,and catalyzing the gas-sensitive reaction process.Increasing the adsorption sites on the surface,modulating the baseline resistance and catalyzing the gas-sensitive reaction process are used to improve the hydrogen gas-sensitive properties of indium oxide.At the same time,the effect of the modification on the surface state of the sensing material and its role in improving the gas-sensitive properties are also investigated in this thesis.The specific research works are as follows.(1)The effect of oxygen vacancies on the sensing performance of In₂O₃-based gas sensors.Oxygen vacancy(V_O)is one of the key factors determining the electrical properties of metal oxide semiconductor-based gas sensors.Numerous studies have concluded that oxygen vacancy plays an important role in improving the sensing performance of metal-oxide-semiconductor-based gas sensors,both in high and low temperature environments.Its presence can increase the active adsorption sites on the surface of sensitive materials,thus increasing the amount of gas adsorption and enhancing the response performance of the sensor.In this thesis,indium oxide nanotubes with high specific surface area and easily tunable conductive channels were prepared by electrostatic spinning method,and based on this method,oxygen vacancies were fabricated by heating hydrogenation to investigate the effect of vacancies and the concentration of vacancies on their gas-sensitive performance.The results show that the presence of oxygen vacancies enhances the sensitive properties of indium oxide samples to different target gases in different degrees,and the response of indium oxide to different target gases increases gradually with the increase of oxygen vacancy concentration.(2)Study on the effect of different concentrations of Pd modification on the surface state of In₂O₃ nanotubes and hydrogen gas-sensitive properties.In addition to thermal hydrogenation,oxygen vacancies can be created in the material by introducing impurity metals.For hydrogen gas detection,indium oxide nanotubes with different concentrations of Pd modification were prepared by electrostatic spinning and UV irradiation impregnation methods in this thesis,and compared with pure indium oxide samples to investigate the effects of Pd modification and the concentration of Pd modification on the hydrogen gas-sensitive performance of indium oxide.The experimental results show that the palladium modification can bring different degrees of improvement to the hydrogen gas-sensitive performance of indium oxide,but the response characteristics do not increase with the increase of palladium concentration,but there is an optimal modification concentration.In this experiment,7 mol%palladium modified indium oxide has the best hydrogen gas sensing performance,and its response to 5 ppm hydrogen gas can reach 37.12 at the optimal working temperature of 240?,indicating that 7 mol%is the optimal concentration of palladium modification.The enhancement of the hydrogen gas-sensitive performance of indium oxide by the palladium modification can be attributed to the electrical sensitization of palladium that plays a role in the resistance modulation of indium oxide and the catalytic effect of palladium chemosensitization on hydrogen adsorption and response.(3)Study of the effect of Pd/Ni bimetallic modification on the surface state and hydrogen gas-sensitive properties of In₂O₃ nanotubes.In order to solve the problems of safety hazards caused by the high operating temperature of the palladium modified indium oxide nanotube hydrogen sensors,this work was based on the previous work,and 7 mol%was chosen as the modification concentration of palladium to investigate the effect of palladium-nickel bimetallic co-modification on the hydrogen gas-sensitive performance of indium oxide.The experimental results show that the palladium-nickel bimetallic co-modification improves the gas-sensitive performance of indium oxide much more than the palladium or nickel monometallic modification,which achieves a response of 487.52 for 5 ppm hydrogen at an optimal working temperature of 160°C and has a very high selectivity for hydrogen.The reasons behind the improved response can be explored into three broad points.First,the formation of a heterojunction between p-type palladium oxide and nickel oxide and n-type indium oxide modulates the base resistance of the device and enhances the response space;second,palladium oxide has a chemical sensitization effect on hydrogen,which increases the adsorption sites of hydrogen and accelerates the response rate of hydrogen;finally,the addition of nickel oxide or the synergistic effect of palladium-nickel bimetal,the adsorption of indium oxide on oxygen increases dramatically,which resulting in a huge leap in the response of indium oxide to hydrogen.