High Capacity Hydrogen Storage in Ca Decorated Graphyne: A First-Principles Study

Abstract

Ca decorated carbon allotropes have a potential for high density hydrogen storage, except that the CaÀgraphene and CaÀfullerenes binding is not strong enough to prevent the formation of a Ca cluster. Using first-principles calculations, we show that Ca can bind strongly to sÀp and sÀp 2 bonded graphyne without the formation of a Ca cluster. This enhanced binding energy is due to the additional in-plane π states which do not exist in the sÀp 2 bonded graphene and fullerenes. The H 2 binding to the CaÀgraphyne system is similar to the CaÀfullerenes system with a maximum of six H 2 molecules per Ca atom and a 0.2 eV per H 2 binding energy which is optimal as hydrogen storage materials. With two Ca atoms per unit cell, this leads to 9.6 wt % hydrogen storage capacity in theory.

The role of density functional theory methods in the prediction of nanostructured gas-adsorbent materials

“…Wang's calculations show that the H 2 binding energies obtained with the vdW-DF method lie systematically below those obtained with GGA-PBE (i.e., stronger molecule-GAM interactions by ∼ 0.05 eV/molecule), and generally above the LDA results (i.e., weaker molecule-GAM interactions by ∼ 0.05 − 0.10 eV/molecule). (Similar conclusions have been attained by other authors in alike Ca-decorated carbon nanomaterials [225,226].) In light of these outcomes, it is argued that long-range dispersion interactions can be also important in the adsorption of hydrogen molecules on chemically modified carbon nanomaterials, even in the cases where the obtained binding energies are large (i.e., |E bind | ≥ 0.1 eV/molecule).…”

“…As for local and semilocal DFT functionals, these two elements are totally missing in them, therefore they are likely to provide unreliable results on the hydrogen storage topic. Situations in which local and semilocal GAM predictions seem to be correct normally are fortuitous and indicate the presence of large energy error cancellations [225,226]. Namely, the sign of the missing contributions to the exchange-correlation energy in local and semilocal approaches are opposite and therefore can compensate each to the other.…”

Improved hydrogen storage in Ca-decorated boron heterofullerenes: a theoretical study

“…[7][8][9][10][11][12][13][14][15][16][17][18][19] In this work, we study the Ca decoration of carbon-boron heterofullerenes. The rst heterofullerenes realized in experiments were boron-doped carbon fullerenes.…”

Expanded Carbon Lattices and Congener Hydrocarbons with directionally Inserted Triple Bonds

“…(23b), a feature that is important in the selectivity towards hydrogen molecules in mixtures with N 2 , O 2 , CO, etc. [69][70][71][72]. Hydrogen and helium molecules differ in dimensions and shape: the ellipsoidal hydrogen molecules have dimensions that are slightly larger than those of spherical monatomic molecules of helium, so that it would be interesting to have experimental data for how mixtures of these two gases would behave towards the carbon lattices illustrated in Fig.…”