Modelling carbyne C12-ring calcium decorated for hydrogen storage

Abstract

We computationally investigate the hydrogen storage properties of C12 carbyne structure decorated with one and up to six calcium (Ca) atoms adsorbed to outer surface. The calculations are carried out by density functional theory DFT with the generalized gradient approximation PW91 (Perdew and Wang) as implemented in the modeling and simulation Materials Studio software. Dmol3 is used to calculate, total energies, charge density HOMO-LUMO and Mulliken population analysis. Based on these results, up to six H2 molecules per Ca atom can be physisorbed with an average binding energy of 0.1272 eV per H2 molecule. The study is extended to a system with six calcium atoms, which can adsorb up to 36 H2 molecules. This leads to 15.87 weight percentage (wt %) for the gravimetric hydrogen storage capacity. According to these results, the calcium-coated carbyne C12 structure is a good candidate for hydrogen storage with application to fuel cells.

Carbyne Ring Activated Using ZnCl2 for Hydrogen Adsorption: DFT Study

“… 19 , 20 , 48 where E C 12 is the total energy of the activated carbyne molecule, E Ca is the total energy per calcium atom, and E Ca x C 12 is the total energy of one carbyne molecule with x Ca atoms. For a single Ca atom, we find three optimal positions around the C 12 -ring to be located in front of either single or triple bonds and also at the center of the ring, with binding energies of 2.79 eV (single and triple bonds) and 3.34 eV (center of the ring), which with respect to the pristine CaC 12 complex 21 represent increases of 25.11% and 49.77%, respectively, which means it is strongly chemisorbed. 47 ( Table 1 ).…”

“…To carry out the analysis of this work, we take the pristine C 12 -ring 21 previously investigated and then we activate with zinc dichloride (ZnCl 2 ) in order to grow the surface area and enhance pore size distribution, with the aim of improving its hydrogen storage properties. The C 12 -ring corresponds to a C 4N structure with N = 3; with a D ( n /2) h symmetry.…”

“…Once the CaC 12 activated complex reaches equilibrium, the next step is the adsorption analysis of H 2 molecules on the decorated complex. Using eqs 4 and 5 , 4 , 18 , 20 , 21 we calculate the average binding energy and adsorption energy of n H 2 molecules adsorbed on the doped complex. where E (Ca x C 12 ) and E ( H 2 ) are the total energies of the Ca x C 12 complex and an isolated H 2 molecule, respectively.…”

“…Previous research has shown that pristine carbyne C 12 -ring decorated with Ca atoms might bind up to six H 2 molecules with average binding energies of 0.18 eV per H 2 (PW91) and 0.32 eV per H 2 with the empirical correction scheme of Grimme (DFT-D). 21 Nevertheless, only a single Ca atom might be bound to the carbyne molecule with binding energy ( E b Ca ) higher than 2 eV, reaching 6.16 wt % for the gravimetric hydrogen storage. Even for cluster C 10 -rings 24 in polyyne and cumulenic forms, only a single Ca atom might be chemisorbed with binding energies greater than 2.5 and 2.33 eV for GGA-PW91 and GGA-PBE functionals, respectively.…”

“…32 Two carbyne structures might be defined as cumulene (equal double bonds) and polyyne (alternative single/triple bonds). 25−32 Previous research has shown theoretical estimation of Ca-decorated pristine carbyne for hydrogen storage on linear chains 18 and rings, 21 which meet the U.S. Department of Energy target requirement of 5.5 wt %. 5 Nevertheless, a single calcium atom can bind with binding energy higher than the cohesive energy, which makes cluster formation energetically favorable in these systems.…”