Preparation And Enhanced Properties Of In₂O₃/Nano-TiO₂ Composite Hydrogen Sensors

The hydrogen element is the most abundant in the universe.Its combustion product is water and its combustion releases high heat free from contamination;whereas,it is colorless,tasteless and highly explosive.Thereby,the safety of its storage is urgently needed.It is of great significance to do research on gas sensor to detect hydrogen.Aiming at the present problem of high work temperature and poor recovery performance of semiconductor hydrogen sensors,this thesis is committed to the study of the property of hydrogen sensitive properties of the sensors in room temperature working environment.It is hoped that the sensor with excellent response time,recovery time,and sensitivity can be obtained through the composite,doping and noble metal catalysis of different semiconductor oxides.The research work of this thesis mainly consists of the following parts:The TiO₂ nanosheets were prepared by hydrothermal method,and In₂O₃/TiO₂tablets with different doping specific gravity were prepared by tableting technology,and systemically study their hydrogen sensive properties.By comparing the Ag electrodes,it was found that under the catalysis of Pt electrodes,the hydrogen sensitivity of the sensor was greatly improved,the minimum response hydrogen concentration reached 1 ppm,and the resistance value changed to 10⁶ orders of magnitude.This is because that the Pt electrode significantly reduces the adsorption activation energy of the sample surface.By comparing the effect of different annealing temperatures on the performance of the sensor,we found that the sample at 600^oC had the best recovery performance;whereas,only the hydrogen with 1000ppm concentration could be found in the sample annealed at 800^oC,and the response and recovery time rapidly increased.The In₂O₃/TiO₂ tablet sensors show enhanced performances comparing with their pure TiO₂ counterparts,and their minimum response hydrogen concentration reached 1 ppm.This is due to the enhanced band bending because of the formation of the n-n homotypic heterojunction between In₂O₃/TiO₂,and good electrical contact and charge transfer at the interface.Having investigated In₂O₃ with different specific gravity,it was found that the composite tablet with 20 wt%In₂O₃ has the best stability,and has both a short response time and recovery time in different concentrations of hydrogen,and its response and recovery time in 1000 ppm hydrogen could reach 5.5 s and 30 s respectively.Through further doping of graphene,TiO₂ tablets doped with 0.1 wt%of graphene were prepared,and it was found that the sensitivity,the sensor's response and recovery time in different concentrations of hydrogen are all unusually excellent with the response and recovery time in 1 ppm hydrogen being 8 s and 10 s,respectively and those in 1000 ppm hydrogen are even as low as 6 s and 2 s respectively.This can be attributed to the large specific surface area and excellent electron-transport ability of graphene.The anodic oxidation method was used to prepare TiO₂ nanotube films,and the effects of different parameters on the structure of nanotubes were investigated.And then In₂O₃ was deposited by centrifugal deposition to investigate its hydrogen sensitivity at room temperature.The TiO₂ nanotube films were prepared using Ti plate as precursor,and 0.75 wt%NH₄F glycerol electrolyzed aqueous solution was used to electrolyze titanium films.By investigating the influence of voltage on the TiO₂ nanotube film,we found that the nanotubes prepared with a voltage of 20 V have larger aperture size and uniform wall thickness not easy to be destroyed.By investigating the effect of oxidation time on the effect of TiO₂ nanotube films,we found that the length of nanotubes with 2 h oxidation reached 1?m,and the surface of the film was relatively smooth.Excessive oxidation time will not only cause excessive height difference of nanotubes,but also make nanotubes grow in a disorderly manner.Finally,through microscopic morphology analysis,we found that the TiO₂ nanotube film produced by using the 20 V voltage anode Ti sheet for 2 h had the most excellent structure and it was centrifugally deposited in 10 mL of In₂O₃,and a sensor was fabricated by sputtering interdigitated platinum?Pt?finger electrodes which was able to detect hydrogen with a minimum concentration of 1ppm,and the response time,at 1000 ppm hydrogen concentration,reached 10 s.The sensitivity at the 100 ppm hydrogen concentration is 0.0407.The introducing of In₂O₃ not only solves the problem of small resistance of the pure TiO₂ nanotube sensors,but also retains the advantages of hollow structures of TiO₂ nanotubes.Meanwhile,the In₂O₃/TiO₂ n-n homotypic heterojunction results in an enhanced bending of the energy band,thus accelerating their sensing responds to hydrogen.At the same time,the In₂O₃/TiO₂ nanotube composite hydrogen sensor also has good recovery performance.