Double layers of H2 adsorption on an AlN sheet induced by electric field

The hydrogen storage properties on a single nano-scale AlN sheet with and without an applied electric field are investigated by using first-principles method based on density functional theory. The H2 molecule on top of a N atom is the most stable adsorption state, while the H2 molecule on top of an Al atom is a metastable one in the absence of an applied electric field. The diffusion barrier of the H2 molecule from the metastable state to the most stable state is about 0.002 eV, which can be easily overcome in experiments. It is found that two layers of H2 molecules can be steadily adsorbed on and below (upper H2 molecules on the N atoms and lower H2 molecules on the Al atoms) the sheet, respectively, by applying a suitable electric field. The reliability of H2 adsorption on the AlN sheet is evaluated by investigating the changes of H2 adsorption energy, bond lengths, and density of states. The stored H2 molecules can be controllably released by reducing the strength of the applied electric field, thus making reversible hydrogen storage on the AlN sheet.