Hydrogen sieving from intrinsic defects of benzene-derived single-layer graphene

Single-layer graphene films, crystallized by chemical vapor deposition, host a low density of vacancy defects that are attractive for the size-sieving of molecules. The size and the density of such defects are a function of the growth temperature and the carbon precursor. So far, the studies applying the intrinsic defects of graphene have only used CH₄ as the precursor. Since there are reports claiming the synthesis of graphene from benzene at low temperature (up to 100 °C on Cu foil), we systematically studied the crystallization of benzene-derived graphene and the evolution of intrinsic defects. We demonstrate that graphene cannot grow from benzene below 700 °C on Cu. We attribute the reports on low-temperature growth of graphene to the practice of pre-annealing of the Cu foil at 1000 °C and to the unintentional benzene residues in the reactor if the reactor is not purged carefully. Finally, we report that high-quality single-layer-graphene can be synthesized using benzene above 825 °C. The majority of vacancy defects in benzene-derived graphene (900–1000 °C) are smaller than 0.38 nm, leading to an attractive H₂ sieving (H₂ permeance over 2000 gas permeation units; H₂/C₃H₈ and H₂/SF₆ selectivities of 12 and 50, respectively).