The hydrogen storage capacity of Sc atoms decorated porous boron fullerene B40: A DFT study

Abstract

The hydrogen storage capacity of transition metal Sc atoms decorated porous boron fullerene B40 is investigated by the pseudopotential density functional method. The B40 cage contains two B6 cavities (diameter: 3.36 Å) and four B7 holes (diameter: 3.68 Å). It is calculated that the structures with the Sc atom outside the hollow sites of these cavities are the most stable. The calculated binding energy of the Sc atom to the B6 and B7 cavities on the surface of B40 are 4.61 and 5.24 eV, much larger than the experimental cohesive energy of bulk Sc (3.90 eV/atom). Moreover, the distance between the neighboring two Sc atoms (5.61 Å) is considerably larger than that of the Sc2 dimer (3.20 Å), therefore, the problem of Sc atoms aggregative to form the Scn cluster is expected to be overcome. The average adsorption energies and consecutive adsorption energies reveal that each Sc atom can most adsorb five H2 molecules. The calculated average hydrogen adsorption energies per H2 for B40(Sc–nH2)6 (n = 1–5) are in the energy range from 0.33 to 0.58 eV, which is suitable for hydrogen storage under near-ambient conditions. The Dewar–Kubas interaction dominates the adsorption of H2 by B40Sc6. The calculated desorption temperature and molecular dynamic simulation indicate that the B40(Sc–5H2)6 structure is easy to desorb H2 molecules. The HGD of the bulk [B40(Sc–5H2)4]4 is 6.18 wt%, a little smaller than that for B40(Sc–5H2)6 (8.3%), however still exceeding the 5.5 wt% at 2017 specified by the US department of energy (DOE). Therefore, the stable B40 structure decorated by the Sc atoms can be applied as one candidate for hydrogen storage materials under near-ambient conditions.