Local structure and dynamics of hydrogen in carbon nano-materials: a neutron scattering and DFT approach

The study of the interaction between hydrogen and carbon monolayers has attracted a remarkable interest in different scientific domains, from interstellar chemistry, to nanoelectronics and energy storage just to name a few. The debate about the peculiar state of hydrogen at the graphene surface is still open and active and has important fundamental and technological issues. It is evident that the behavior of a chemically absorbed H atom at the graphene surface depends on different parameters, like the chemical bonds and the local atomic environment. The latter properties are specific to the graphene samples studied, namely to their preparation and further processing, as well as to the hydrogenation stage. Recently, the development of chemical methods, which exploit the thermal exfoliation of graphite oxide for producing gram-scale amount of graphene (TEGO), has opened the routes towards the experimental investigations of graphene using techniques that are usually reserved to bulk systems, like neutron scattering. In this work, macroscopic amount of graphene are studied using neutron scattering (neutron diffraction and spectroscopy). We show that the hydrogen local environment can be efficiently characterized, both qualitatively and quantitatively, thanks to its in influence on the dynamics of the chemisorbed hydrogen atoms. The combination of experimental data and ab-initio DFT calculations allows to identify the spectral fingerprints of the specific C-H configurations located at in-plane defects onto the graphene plane. The temperature dependence of the neutron spectra, coupled to 1H-NMR investigations, reveals an activated evolution of the structure of the in-plane voids, with a surprisingly low activation barrier. Finally, we extend the neutron studies to other type of carbon nanostructures, in particular to Nickel-decorated graphenes and to Lithium-intercalated fullerides, all of them being material relevant to hydrogen storage.