Direct measurement of the amount of dissociated hydrogen atoms attached on graphene

Recently, we reported n-type graphene can be achieved simply using H₂ molecules. It was understood by the attachment of hydrogen atoms dissociated on the surface of graphene. However, the amount of attached hydrogen has not been yet investigated. Here, we show the possibility of the formation of C-H bonds due to the H₂ exposure theoretically and the mass of the attached hydrogen atoms on graphene experimentally. The amount of the attached hydrogen atoms has been measured by a quartz crystal microbalance (QCM). After exposure of a multilayer graphene (MLG) to 20 bar of H₂ pressure at 353 K for 20 h, the resonance frequency (RF) of QCM decreased. It indicates that the mass of the MLG increases. On the basis of the RF variation, we concluded that the hydrogen atoms were bonded to 3.84% of carbon atoms in the MLG. In order to confirm the C-H bonding of MLG, Raman spectroscopy was performed before and after exposure to H₂ pressure. On exposure, the D peak developed and the peak for 2-D graphite in 2D band increased. The experimental results and theoretical calculation demonstrate that the H₂ molecules on the surface of the graphene are dissociated and that some of dissociated H atoms are attached on graphene.