Hydrogen storage in Al-N cage based nanostructures

Recent efforts have been devoted to design new materials with exposed metal sites for hydrogen storage. Different from bulk AlN having the wurtzite structure and fourfold coordination, the Al sites in AlN cages are unsaturated and have threefold coordination, resulting in a storage weight percentage of 4.7%, while the adsorption energy of H2 molecules can be controlled by the relative ratio of the unequivalent Al sites. A general expression of the adsorption energy is derived from first-principle calculations, which gives a guideline for tuning the structure to reach the desirable energy range for the storage operation under ambient thermodynamic conditions.