Nanostructured graphite/Li-N-H based composite materials for hydrogen storage

Ball-milled hydrogenated graphite and LiNH2+LiH are considered potential materials for solid state hydrogen storage. This work investigates the structural and dehydrogenation properties of ball-milled graphite and composites of 2graphite+LiNH2, LiNH2+1.2LiH and 2graphite+LiNH2+1.2LiH. Characterization of the as-milled materials showed the formation of a nanocrystalline/amorphous mixture in the composites. A higher ball-milling rotation speed led to a smaller crystallite size for graphite. Decomposition of the as-milled graphite was performed by heating to 950 °C at 2 °C /min. Graphite milled for 10 h released 2.2 wt. % H2 at onset temperature of 350 °C, indicates the presence of C-H bond in the hydrogenated graphite. A large amount of H2 was released during the heating of graphite+LiNH2, as opposed to the release of NH3 during the decomposition of as-received LiNH2. Dehydrogenation of 2graphite+LiNH2+1.2LiH was performed by heating to 500 °C at 2 °C /min. The onset temperature of hydrogen decomposition was reduced to 80 °C-95 °C. In-situ XRD shows the presence of Li2NCN above 350 °C, with no Li2C2 or Li2NH detected. The formation pathway of this new phase is not clear, but it presumably must involve a reaction between graphite and a Li-N-H compound