Be, Li and Sc functionalized borane B ₆ H ₆ and carborane C ₂ B ₄ H ₆ for hydrogen storage: A comparison using first principles approach and molecular dynamics simulations

Abstract

Hydrogen adsorption properties of functionalized closo-dicarborane (C 2 B 4 H 6) and boranes (B 6 H 6) are studied and compared using quantum chemical methods. More number of H 2 molecules gets adsorbed on metal functionalized carboranes than metal functionalized boranes considered in this work. One, three and five H 2 molecules get adsorbed on each metal atom in B 6 H 4 Be 2 , B 6 H 4 Li 2 and B 6 H 4 Sc 2 complexes, respectively. One additional H 2 molecule per metal atom gets adsorbed on C 2 B 4 H 4 Be 2 , C 2 B 4 H 4 Li 2 and C 2 B 4 H 4 Sc 2 complexes than B 6 H 4 Be 2 , B 6 H 4 Li 2 and B 6 H 4 Sc 2 complexes, respectively. The H 2 uptake capacity of C 2 B 4 H 4 Be 2 , C 2 B 4 H 4 Li 2 and C 2 B 4 H 4 Sc 2 complexes is found to be 8.28, 15.92 and 13.04 wt%, respectively, whereas that of B 6 H 4 Be 2 , B 6 H 4 Li 2 and B 6 H 4 Sc 2 complexes is found to be 4.43, 12.75 and 11.26 wt%, respectively. Adsorption energy values reveal that though more number H 2 molecules get adsorbed on metal functionalized carboranes H 2 adsorption on metal functionalized carboranes is thermodynamically unfavourable even at very low temperature whereas it is favourable on B 6 H 4 Be 2 , B 6 H 4 Li 2 , and B 6 H 4 Sc 2, below 185, 110 and 170 K respectively. B 6 H 4 Be 2 , B 6 H 4 Li 2 , and B 6 H 4 Sc 2 as well as C 2 B 4 H 4 Be 2 , C 2 B 4 H 4 Li 2 , and C 2 B 4 H 4 Sc 2 complexes are not promising materials for hydrogen storage at room temperature. However, metal doped B 6 H 6 are promising candidate for hydrogen storage at low temperature and 1 atm pressure. For Be, Li and Sc doped B 6 H 6 the H 2 adsorption is thermodynamically favourable below 185, 110 and 170 K, respectively. Zero point energy correction has the larger effect on H 2 adsorption energy for Be, Li and Sc functionalized borane than Be, Li and Sc functionalized carborane.

First-Principles Study of Hydrogen Storage of Sc-Modified Semiconductor Covalent Organic Framework-1

“…The parameters are set to a constant number of atoms, a constant volume, and constant temperatures of 300 and 400 K. We set the MD simulation time to 1.5 ps to have enough time to complete the calculation, which is consistent with the published reports. 56 , 63 , 68 − 70 Figure 9 a,b shows the molecular dynamics simulation results of the adsorption of 24 H 2 molecules by 6Sc-COF-1 at 300 and 400 K, respectively. It can be seen that the COF-1 structure does not undergo significant deformation and the six Sc atoms are still stably adsorbed on the COF-1 layer without aggregation at both 300 and 400 K. One of the four hydrogen molecules adsorbed by each Sc atom escapes at 300 K, and all of the adsorbed H 2 molecules are released when the temperature is 400 K. It is demonstrated that the adsorption and desorption of hydrogen molecules can be achieved within a narrow temperature range of 300–400 K and 6Sc-COF-1 has excellent reversibility as a hydrogen storage material.…”