Hydrogen Sensor Research On Platinum-based Bimetal/carbon Nanocomposites

Hydrogen is favoured by many industries as a clean and renewable energy source,and is hailed as the energy of the future because of its efficient combustion and non-polluting products.However,as an energy source that exists in a gaseous state at room temperature,its safety is a major concern.Hydrogen has an ignition energy of 0.019 m J and poses a risk of explosion when the volume fraction in air exceeds 4%.At the same time,hydrogen,as the molecule with the lowest known mass fraction and smallest volume,is extremely active in the gaseous state and is highly susceptible to leakage;it is also colourless and odourless,making it difficult to detect a leak at the first opportunity.It is therefore particularly important to develop hydrogen sensors with a fast,wide range response for real-time monitoring.Carbon nanofibers（CNFs）have unique physicochemical properties,such as large specific surface area,high carrier mobility and abundant surface active sites,it is both a conductive carrier and a three-dimensional skeleton with high mechanical strength,which can be modified for the attachment of different gas-sensitive materials to form highly selective and sensitive carbon nanofiber-based composite films for room temperature detection of gases.Platinum（Pt）is an excellent hydrogen catalyst with high adsorption and selectivity for hydrogen,and Pt-based bimetallic materials are able to achieve enhanced gas-sensitive performance in a synergistic effect.Therefore,loading Pt-based bimetallic nanoparticles on the surface of carbon nanofibers can both promote the diffusion and adsorption of gas molecules on CNFs composite films and accelerate the charge transfer in the adsorption process to improve the response rate.Based on the above discussion,the specific research of this thesis is as follows.Firstly,the adsorption characteristics of CNFs composite films with different metal modifications on hydrogen were investigated by simulation.The theoretical models of monometallic（Au,Ag,Cu,Ni,Pt）/CNFs composite films and bimetallic Pt-Cu/CNFs composite films were established,and the whole process of hydrogen adsorption-dissociation on the surface of the above theoretical models was calculated by VASP simulation based on the basic physical properties of atomic nuclei and electrons outside the nucleus from the first nature principle.The facilitation of metal modification on hydrogen sensing by carbon nanofibres was revealed and the catalytic role of Au,Ag,Cu,Ni and Pt metals in heterostructure formation,hydrogen adsorption and dissociation was analysed.Comparing the simulation data,the bimetallic Pt-Cu/CNFs composite structure is the best choice for the preparation of hydrogen sensors.On this basis,CNFs membranes were prepared by electrostatic spinning and heat treatment processes,and Pt-Cu bimetallic nanoparticles were grown simultaneously on the surface of CNFs by liquid-phase growth method to construct Pt-Cu/CNFs composite gas-sensitive materials,and the effect of the regulated liquid-phase growth process on their H₂ gas-sensitive properties was investigated.The results show that the preferred Pt-Cu/CNFs sensor has high sensitivity,fast response/recovery speed,wide gas-sensitive response range and strong anti-interference capability.However,the poor chemical stability of the Cu metal in this composite leads to a lack of long-term stability of the sensor.Then,to address the problem of easy oxidation of nano-Cu,the composite films with shell-Pt-Cu/CNFs cladding structure were prepared by electrochemical deposition and replacement methods respectively,and characterization analysis of material surface microscopic morphology,alloy crystal structure,element content and thermal stability was carried out,followed by the study of sensor H₂ gas-sensitive performance at room temperature.The results show that Cu in the bimetallic carbon nanofiber composite film can not only solve the problem of Pt spontaneous agglomeration in solution to a certain extent,but also increase the active adsorption sites on the surface of the carbon nanofiber,and interact with Pt to form new electronic channels to accelerate the charge transfer during the adsorption and desorption process.The results of gas sensing tests show that the shell-Pt-Cu/CNFs bimetallic sensor has high sensitivity,fast response/recovery speed,lone service life and can quickly and effectively detect low concentrations of H₂ at room temperature.The research in this thesis provides a basis for the practical application of hydrogen sensors.