Reversible hydrogen adsorption on Li-decorated T-graphene flake: The effect of electric field.

In the present work, we have studied a new allotrope of graphene, denoted as T-graphene (TG) flake as a versatile material in hydrogen storage. Recently, the metallic character of TG has been revealed. Our results show that the Li-decoration has a significant effect on the electronic properties of TG flake. Our density functional theory (DFT) calculations exhibit that the energy band gap of TG flake is decreased by decorating of the Li atom. Hydrogen adsorption on Li-decorated TG flake (Li/TG) under the influence of different external electric fields (EFs) is also explored by DFT calculations. We found that the hydrogen adsorption on the Li/TG increases when the positive EF is applied. Our results also show that the adsorption energy of the hydrogen on the Li/TG can be gradually enhanced by increasing the applied positive external EF along with the charge transfer direction. Moreover, Li atom in the Li/TG shows the high hydrogen capacity up to six H2 molecules. On the other hand, the H2 adsorption on the Li/TG is remarkably decreased by applying the negative EFs to the Li/TG. Therefore, the H2 adsorption/release procedure on the Li/TG are reversible and can be tuned by applying the appropriate EFs. Our study exhibits that the Li/TG is a promising material for reversible adsorption and release of H2.

Tuning the field emission and electronic properties of silicon nanocones by Al and P doping: DFT studies.

The effect of replacing an Si atom of a silicon nanocone (SiNC) by Al or P atom on its electronic and field emission properties was investigated using density functional theory calculations. Molecular electrostatic potential surface indicates that the electrons do not spread out on the surface of SiNC evenly, and they tend to accumulate more at the apex, facilitating the electron emission from this site. Replacing an Si atom of the apex of nanocone by Al and P atoms is energetically more favorable than that of the wall by about 12.0 and 8.8 kcal/mol, respectively. Both Al- and P-doping processes increase the SiNC electrical conductivity, but the electron emission from the surface of SiNC increases after the P-doping and decreases by Al- doping. The electron emission in the P-doped SiNC is predicted to be about 600 times greater than that of the pristine SiNC at room temperature. The Al- or P-doping makes the SiNC a p-type or n-type semiconductor.