Light metal decorated graphdiyne nanosheets for reversible hydrogen storage.

The sensitive nature of molecular hydrogen (H) interaction with the surfaces of pristine and functionalized nanostructures, especially two-dimensional materials, has been a subject of debate for a while now. An accurate approximation of the H adsorption mechanism has vital significance for fields such as H storage applications. Owing to the importance of this issue, we have performed a comprehensive density functional theory (DFT) study by means of several different approximations to investigate the structural, electronic, charge transfer and energy storage properties of pristine and functionalized graphdiyne (GDY) nanosheets. The dopants considered here include the light metals Li, Na, K, Ca, Sc and Ti, which have a uniform distribution over GDY even at high doping concentration due to their strong binding and charge transfer mechanism. Upon 11% of metal functionalization, GDY changes into a metallic state from being a small band-gap semiconductor. Such situations turn the dopants to a partial positive state, which is favorable for adsorption of H molecules. The adsorption mechanism of H on GDY has been studied and compared by different methods like generalized gradient approximation, van der Waals density functional and DFT-D3 functionals. It has been established that each functionalized system anchors multiple H molecules with adsorption energies that fall into a suitable range regardless of the functional used for approximations. A significantly high H storage capacity would guarantee that light metal-doped GDY nanosheets could serve as efficient and reversible H storage materials.