Effect of temperature on hydrogen sorption of crumpled graphene with structural elements different sizes
High strength, thermal and electrical conductivity, and also many other properties of carbon materials make them unique, due to which today these materials are widely used in many industries. Three-dimensional graphene-based materials, including crumpled graphene (CG), have a high specific surface area and porosity. These properties open up the possibility of using such structures in hydrogen power engineering as a medium for storing and transporting hydrogen.
It has been established in many works that the sorption capacity of CG depends on the degree of hydrostatic compression and temperature. However, the influence of the graphene flakes sizes that consist the CG has not been studied widely enough. It was shown in our early works that the larger the volumetric surface area of graphene flakes, the higher its hydrogen sorption will be. At the same time, hydrostatic compression improves these indicators. In this work, the effect of temperature on the physical sorption of hydrogen in crumpled graphene with different sizes of carbon flakes СG (7,7) and СG (15,15) is considered. The nanotubes chirality from which the flakes were created is indicated in parentheses. Hydrogenated CGs were subjected to hydrostatic compression to ε = 0.77, followed by heating from 0 to 500 K. Molecular dynamics simulation was carried out using the free and widely used LAMMPS software package with AIREBO interatomic potential. It was effectively used in the study of deformation processes in three-dimensional carbon structures, as well as in the study of hydrogen sorption in these nanostructures It was found that the deformed СG (15,15) begins to dehydrogenation at 100 K, and hydrogen begins to escape from the undeformed structure at T = 50 K. The dehydrogenation of the CG (7,7) structure begins at 150 K and is practically independent of the structure compression . However, long annealing (t = 20 ps) at 77 K leads to rapid dehydrogenation of the CG structure (7,7), compared with CG (15,15). This is since the adsorbed surface area (hydrogen atoms are deposited on it due to van der Waals forces) is smaller in the first case than in the second.
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Bashkir State University
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