| Low dimensional materials, especially low dimensional nano-carbon materials, havebeen the hot topics in the material science. Graphene as a2D hexagonal material occupied bysp2carbon atoms has been of great interest in theory and experiment because of its uniquemechanical, thermal and electronic properties since its discovery in2004. After thediscovering of graphene, a new carbon allotrope graphyne has been prepared byexperimenters. Different from graphene, graphyne is a new type of2D carbon allotropesincluding both sp and sp2hybridized states which has more abundant carbon bonds. As aconsequence of the introduction of acetylenic linkage, graphyne possesses many differentproperties from graphene. It is worth noting that graphyne may perform better than graphenesuch as its natural hollow structure and low thermal conductivity. With a growing worldpopulation and an increasing standard of living, the world is running out of fossil fuels andthere has never been a time when the demand for clean and sustainable energy was greater.Graphyne may be a promising material because of its unique properties. In this article, wemainly paid our attentions on investigating lithium storage on graphynes and thermalconductivities of graphyne nanotubes, hoping to provide certain theoretical help for the fieldsof lithium ion batteries and thermoelectric materials. Our results list as follows:(1) Graphyne, which contains planar sheets equally occupied by sp2and sp carbon atoms,is a layered carbon allotrope. Since the length of the acetylene chains within graphyne can bevariable by adjusting the number of acetylenic linkages (C≡C) between carbon hexagons,resulting in a family of graphyne. In this work, density functional theory (DFT) calculationsare carried out to investigate the adsorption of lithium atoms on graphynes monolayers, andthe results are compared to extrapolate the potential relationship between lithium storagecapacity and the number of acetylenic linkages. After comparison, we found that furtherextending the acetylenic chains might not be helpful in achieving higher capacity. The longeracetylene chains result in the lower carbon atom density, as well as the lower stability of thecarbon networks, which should be taken into consideration seriously. High-capacity Li storageas LiC3in graphdiyne and graphyne-5has been achieved, and the preferred adsorption sitesfor Li have been identified computationally. With high Li storage capacity and structuraladvantages, these porous carbon materials are expected to be applied in efficient lithiumstorage.(2) Similar to rolling up graphene to form carbon nanotube, graphyne also can be rolledup to form graphyne nanotube (GNT). By adjusting the number of acetylenic linkages between the nearest-neighbouring carbon hexagons, a family of graphyne nanotubes labelledas GNT-n where n is the generation number can be formed. Thermal conductivities (TCs) ofGNT-n were investigated by non-equilibrium molecular dynamics simulations. The influencefactors of chirality, generation number, diameter and length on the TC of GNT-n werediscussed in detail. Simulation results indicate the chiral dependence of TCs of GNT-n is veryweak and there is no difference between the TCs of armchair and zigzag GNT-n. With theincrease of generation number n, TC decreases and scales as~n0.57. The diameter of thegraphyne-n nanotubes has a weak impact on TC and the TC of GNT-n scales as~d0.03atd>5nm for all GNT-n. With the increase of the length of GNT-n, TC increases and scales as~L. There is a crossover in the scaling relation between TC and L and two differentscaling exponents are clearly observed for all GNT-n and CNT. TC values of GNT-n areestimated to be92.4,43.6,30.4,27.4,23.0W/(mK) for n=1～5, respectively, at L=2.6μm byextrapolation, which are two orders of magnitude smaller than2820.6W/(mK) of the CNTwith the same length. This implies GNT may be more promising thermoelectric materials thanthe CNT. |
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