Exotic Geometrical and Electronic Properties in Hydrogenated Graphyne

Abstract

On the basis of first-principles calculations, we present exotic geometrical and electronic properties in hydrogenated graphyne, a 2D material of sp-sp2 hybrid carbon networks. Hydrogen atoms adsorbed onto sp-bonded carbon atoms can form both sp2-and sp3- hybridized bonds and can exist in three different geometries: in-plane, out-of-plane, and oblique-plane; this is in sharp contrast to hydrogenated graphene, which has only one hydrogenation geometry. The band gaps of hydrogenated graphyne can vary by ∼3 eV as the geometry changes. We also find that change in the hydrogen concentration allows a large band-gap tuning of ∼5 eV. Unlike hydrogenated graphene, in which H atoms show a tendency to cluster, H atoms tend to be dispersed in graphyne, making band-gap tuning feasible. These exotic properties in hydrogenated graphyne indicate that the band gap of hydrogenated graphyne can be tailored for new device applications. Furthermore, the composite of fully hydrogenated graphyne is C1H 1.75, which has a hydrogen-to-carbon ratio greater than that of graphane (C1H1). This large hydrogen capacity (∼13 wt % H) suggests that graphyne also can be used as a high-capacity hydrogen storage material.