Simple and Binary Hydrogen Clathrate Hydrates: Synthesis and Microscopic Characterization through Neutron and Raman Scattering

The search for efficient hydrogen-storage materials has led to an increasing interest in hydrogen clathrate hydrates, since it has been demonstrated that an appreciable amount of molecular hydrogen can be stored in the water cages and released at melting. Different synthetic routes have been followed to maximize the quantity of trapped hydrogen and to speed up the kinetics of the clathrate formation. Here, we describe two different synthetic routes for the production of hydrogen clathrate hydrates. Then we present the results of inelastic neutron scattering and Raman light scattering experiments on simple (i.e. containing only hydrogen) and binary (i.e. with a second guest molecule) clathrates. For each class of compounds, we have obtained spectroscopic information on the motion of hydrogen inside the cages, on the occupancy of the cages by hydrogens, and on lattice dynamics. Finally, we have investigated the clathrate crystal stability and the hydrogen release as a function of temperature by means of neutron diffraction.