Molecular Simulation Of Heterogeneous Interfacial Connection Strength And Hydrogen Permeability In Hydrogen Storage Cylinder Liners

As the most promising clean energy in the 21 st century,hydrogen energy has a great role in addressing global climate change and the "double carbon" target.Hydrogen energy is widely used,and hydrogen fuel cell vehicles will effectively reduce environmental pollution,while safe and reliable on-board hydrogen storage cylinders are the key to decide whether hydrogen fuel vehicles can be widely used.70 MPa type IV hydrogen storage cylinders have the advantages of small weight-to-volume ratio and high hydrogen storage density per unit mass,which become the current development trend.Because of the special structure of cylinder liner,the mouth of cylinder and the liner belong to different materials,so it is important to study the connection strength of heterogeneous interface and the permeability of hydrogen gas in cylinder liner.In this thesis,we take gas cylinder lining as the starting point for the study,using molecular dynamics(MD)simulation method and applying Materials studio 2018 software to modify the resin lining to ensure that the toughness and comprehensive mechanical properties of the lining material meet the requirements of the mission standard,and to conduct theoretical studies for the optimal selection of the lining material.Then the bottle mouth is nanosized,so that the surface of the bottle mouth forms pores of different sizes,also called nano-pores,and the contact angle test also shows that the wettability of the bottle mouth is improved,and the formation of "anchor" like structure at the heterogeneous interface can enhance its connection strength.On this basis,the microstructure model of the interface between the bottle mouth and the liner was established by using MD simulation method,the bonding process of the nano-molded heterogeneous interface,the influence of interfacial energy and shear stress on the connection strength were analyzed,and the injection molding process parameters to enhance the interfacial connection strength were studied.Finally,MD simulations were used to investigate the hydrogen permeation behavior under different modified liners,and the solubility parameters,free volume fraction and hydrogen diffusion coefficient of the modified liners were analyzed to explain the diffusion mechanism of hydrogen molecules in the liners from a microscopic perspective,and to investigate the effects of graphene,carbon nanotube fillers and working pressure on the gas barrier properties of the liners.The above three aspects of research are interlinked with each other,which together affect the connection performance of the interface between the bottle mouth and the liner and guarantee the overall gas tightness and stability of the gas cylinder.The research results show that in the study of modified liner,the addition of carbon nanotube functional filler in the liner can not only improve the mechanical properties of the liner and increase the overall stiffness and toughness of the liner,but also reduce the diffusion rate of hydrogen,and the hydrogen diffusion coefficient is reduced by about 45% compared with the unmodified model to achieve low leakage and high recycling of hydrogen.In the injection-molded structure of the interface between the gas cylinder mouth and the liner,the bonding strength can be improved by increasing the contact area of the mouth surface,when the interface energy reaches a maximum value of1972.64kcal/mol,and it is known from the radial distribution function that the heterogeneous interface is connected by hydrogen bonding,chemical bonding,van der Waals force and electrostatic force.