High-capacity hydrogen storage in Al-adsorbed graphene

Abstract

A high-capacity hydrogen storage medium---Al-adsorbed graphene---is proposed based on density-functional theory calculations. We find that a graphene layer with Al adsorbed on both sides can store hydrogen up to $13.79\text{ }\text{wt}\text{ }\mathrm{%}$ with average adsorption energy $\ensuremath{-}0.193\text{ }\text{eV}/{\text{H}}_{2}$. Its hydrogen storage capacity is in excess of $6\text{ }\text{wt}\text{ }\mathrm{%}$, surpassing U. S. Department of Energy (DOE's) target. Based on the binding-energy criterion and molecular-dynamics calculations, we find that hydrogen storage can be recycled at near ambient conditions. This high-capacity hydrogen storage is due to the adsorbed Al atoms that act as bridges to link the electron clouds of the ${\text{H}}_{2}$ molecules and the graphene layer. As a consequence, a two-layer arrangement of ${\text{H}}_{2}$ molecules is formed on each side of the Al-adsorbed graphene layer. The ${\text{H}}_{2}$ concentration in the hydrogen storage medium can be measured by the change in the conductivity of the graphene layer.