DFT study of coinage metal-hydrogen associations as hydrogen storage materials stabilized by weakly coordinating anions

摘要

Density Functional Theory (DFT) calculations were employed to study a series of coinage metal-hydrogen associations formulated as [M(H-2)(n)][A] (M = Cu-I, Ag-I or Au-I, n = 1-5). The [M(H-2)(n)][A] salts utilize both their anions and cations for H-2 storage. The [M(H-2)(n)](+) cations could be stabilized in the solid state by voluminous counter-anions, i.e. the [(H3B) (BH2NH2)(5)(NH2)](-), [B(CNBH3)(3)](-) and [B12H12](-) anions. The estimated bond dissociation energies (BDEs) of the M center dot center dot center dot eta(2) -H-2) bonds are 5-17, 4-11 and 1-26 kcal/mol for the [Cu(H-2)(4)](+), [Ag (H-2)(4)](+) and [Au (H-2)(4)](+) cationic species respectively, while the fifth H-2 molecule is estimated to be very loosely associated to the metal center. Four H-2 molecules could be exploited from the [Cu(H-2)(n)][A] and [Ag (H-2)(n)][A] molecules in addition to the amount of H-2 stored in the anion [A](-). Among the [M(H-2)n][A] salts optimal gravimetric, kinetic and thermodynamic properties and relatively low cost, are predicted for [Cu(H-2)(n)][(H3B)(BH2NH2)(5)(NH2)]. (C) 2019 Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC.