Strong physisorption site for H2 in K- and Li-doped porous carbons.

Molecular hydrogen adsorption between two Li, K-doped coronene molecules (taken as local environment of carbon microporous materials) is studied by first-principles DFT-B3LYP calculations. These cluster calculations are complemented with periodic DFT-LDA/GGA calculations on extended Li- and K-doped structures. In all cases, energy minimization calculations unravel that there is a stable adsorption site for molecular hydrogen in these Li- and K-doped sp(2) carbon structures with large adsorption energies. This is the direct consequence of the significant charge transfer from the doping agents on neighboring slab carbon atoms, which allows the coupling of the molecular H(2) polarizability with the resulting substrate electric field (polarization interaction) that in turn induces the stabilization of molecular hydrogen. These calculations also give an insight on the atomic configurations of interlayer species (H(2) and LiK) as the interlayer spacing increases. It can be shown that large positional changes correlate with electronic properties of interlayer species. The confined hydrogen molecule does not show any tendency for dissociation and adopts a position in the interlayer void that is deeply related to that of doping ions.