Evidence for Site-Specific Reversible Hydrogen Adsorption on Graphene by Sum-Frequency Generation Spectroscopy and Density Functional Theory

AlSalem, Huda, Just-Baringo, Xavier, Larrosa, Igor, Monteverde, Umberto, Jiang, Xingxing, Feng, Yexin and Koehler, Sven PK (2019) Evidence for Site-Specific Reversible Hydrogen Adsorption on Graphene by Sum-Frequency Generation Spectroscopy and Density Functional Theory. The Journal of Physical Chemistry C, 123 (42). pp. 25883-25889. ISSN 1932-7447

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Abstract

We have characterized the C−H stretching vibrations of hydrogenated graphene on gold substrates using vibrational sum-frequency generation (SFG) spectroscopy. These C−H stretches are red-shifted as compared to aliphatic C−H stretches, and SFG signal intensities of the C−H vibrational features increase with increasing hydrogen coverage. By comparison with density-functional theory (DFT) calculations, we conclude that hydrogen atoms covalently attach to the graphene lattice from above the graphene sheet; preferential binding motifs are dimers in the ortho and para positions. SFG spectroscopy is hence not only able to detect hydrogen atoms on graphene at sub-monolayer coverage but it can also serve to obtain relative information about the surface coverage, and in combination with DFT can reveal information about binding motifs.