Thermodynamic and structural properties of ball-milled mixtures composed of nano-structural graphite and alkali(-earth) metal hydride

Hydrogen desorption properties of mechanically milled materials composed of nano-structural hydrogenated-graphite (CnanoHx) and alkali(-earth) metal hydride (MH; M = Na, Mg and Ca) were investigated from the thermodynamic and structural points of view. The hydrogen desorption temperature for all the CnanoHx and MH composites was obviously lower than that of the corresponding each hydride. In addition, the desorption of hydrocarbons from CnanoHx was significantly suppressed by making composite of CnanoHx with MH, even though CnanoHx itself thermally desorbs a considerably large amount of hydrocarbons. These results indicate that an interaction exists between CnanoHx and MH, and hydrogen in both the phases is destabilized by a close contact between polar C-H groups in CnanoHx and the MH solid phase. Moreover, a new type of chemical bonding between the nano-structural carbon (Cnano) and the Li, Ca, or Mg metal atoms may be formed after hydrogen desorption. Thus, the above metal-C-H system would be recognized as a new family of H-storage materials.