The energies and temperature-dependent dynamics of hydrogen and lithium chemisorption on a silicon nanosheet, called silicene, were studied using density functional theory and molecular-dynamics (MD) simulations. Silicene has a buckled honeycomb structure, and has been fabricated as suspended monolayer sheets and nanoribbons in recent experiments. We calculated the adsorption energies of hydrogen and lithium on silicene for different adsorption ratios between 3.1% and 100%. The studies will clarify the characteristics of these novel and promising nanomaterials, and pave the way for their applications.
For Hydrogen, the adsorption energy had a maximum of 3.01 eV/H for complete hydrogenation, and decreased by 24.5 % to 2.27 eV/H for single atom adsorption on a 32-silicon-atom supercell. It was determined that the preferred hydrogen adsorption patterns were clusters. Molecular dynamics simulations revealed the stability of adsorption configurations at 300K. The electronic structure of these stable configurations could be modified and controlled through partial and complete hydrogenations, and a transformation from zero-gap semiconductor to insulator was observed.
For lithium on silicene, the adsorption energy had a maximum of 2.23 eV/Li for 50% lithiation and decreased by 29.6% to 1.57 eV/Li for 100% lithiation. For partial Lithium adsorptions up to 50%, the preferred adsorption sites were hollow sites on top of silicon hexagons. This preference changed as more lithium atoms were introduced. At a 100 % adsorption ratio, the lithium atoms adsorbed to sites directly above or below the silicon atoms. Unlike hydrogenated silicene, the band structure of each partially lithiated structure was shown to be that of a metal.
Combining hydrogen and lithium adsorptions, it was shown that silicene-Li nanocompounds can be considered for hydrogen storage.