Study On Surface Acoustic Wave Hydrogen Sensor Based On Graphene Sensitive Film

Currently,due to more serious air pollution,hydrogen,which is considered to be a clean and reproducible energy source,has been given high consideration in industry and daily life.However,hydrogen is colorless,odorless,flammable and explosive gas,which cannot be easily detected in the case of leakage.Thus,a hydrogen sensor that can detect trace leakage is urgently required.It is reported that graphene possesses special properties as extremely high specific surface area and carrier mobility,which exhibits wide application prospect in the field of gas sensing.In this work,we study surface acoustic wave(SAW)hydrogen sensors based on graphene sensitive films.Reduced graphene oxide(RGO)is prepared by chemical oxidation reduction method,and a layer of platinum(Pt)acting as a catalyst is grown on the surface of the RGO by magnetron sputtering method.In this case,a surface acoustic wave for hydrogen detection is created based on platinum decorated graphene(Pt/RGO)sensitive film.Finally,the fabricated hydrogen sensor is tested under different conditions,which demonstrates that the sensor exhibits a much higher sensitivity than those obtained in the sensors based on sensitive film of metallic oxides.The minimum detectable limit of the Pt/RGO based hydrogen sensor can reach 5 ppm.The thesis covers four parts as follows:In chapter 1,The background of the study is introduced,including the concept and characteristics of graphene,the classification of hydrogen sensors,the development of ultrasonic sensors and the research progress of SAW sensors based on graphene sensitive films.In chapter 2,we design SAW delay lines and prepare Pt/RGO sensitive films on the delay lines.Graphene oxide is prepared by modified Hummers method,and solutions of reduced graphene oxide are obtained using hydrothermal reduction method,which is deposited on the surfaces of SAW delay lines.Furthermore,platinum,working as a catalyst,is deposited on the surface of the reduction graphene oxide.Then,a SAW hydrogen sensor based on a Pt/RGO sensitive film is created.Phase and morphology characterizations show that graphite is completely oxidized,and the graphene oxide obtained through stripping process has fewer layers and good morphology.Then,the RGO obtained through reduction process has a large number of folds.In this case,the RGO provides massive points of attachment for Pt nano-particles,which is favorable to the performance of the SAW hydrogen sensor.In chapter 3,a system is set up to test our SAW hydrogen sensor.The hydrogen sensing measurements are carried out under different conditions,and the mechanisms of sensing and optimized condition for high performance of the sensor are discussed on account of the experimental results.It is observed that when the sensor is operating in Ar environment,it exhibits a much higher sensitivity than it does in air environment.On the other hand,the recovery effect in moist gas is better than that in dry gas.Thus,we find that oxygen and water exert great influences on the response and recovery of the sensor.Finally,the summary of the thesis and the plans for the future work are presented in chapter 4.