High Pressure Synthesis of Novel Hydrides with High Hydrogen Content for Fuel Cell Vehicle

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The purpose of this study is to explore new hydrides of the Mg-RE systems (RE= La, Ce, Pr, Nd) and Mg-TM systems (TM= Ti, Vr, V, Mn, Fe, Co, Ni, Cu, Zn) using the cubic anvil-type apparatus, for the usage for the future fuel cell vehicle.For MgH_2 -x ml% LaH_3, the new hydride was obtained in the range of 25<=x<= 33. The hydrogen content of the new hydride with x=25 was found to be 4.1mass%H, which is corresponding to Mg_3LaH_9, by means of fusion extraction analysis. The crystal structure of newly found hydrides of Mg_3LaH_9, was a primitive tetragonal with a lattice parameter of a=0.8193nm, c=0.5028 nm. The hydrides showed an endothermic peak at around 620K, which decreases with increasing La content.Mg-Ce-H and Mg-Pr-H systems were also explored. Mg_3CeH_9 and Mg_3PrH_9 with a primitive tetragonal structure were synthesized as new compounds under 5GPa. The crystal structures of newly found hydrides of Mg_3CeH_9 and Mg_3PrH_9, was a primitive tetragonal with a lattice parameter of a=0.8118nm, c=0.4979 nm, and of a=0.8118nm, c=0.4979nm, respectively. The hydrogen contents of these hydrides were 3.7 and 3.9mass%, respectively.In Mg-Ni system, Mg_4-Ni compound belonging to space group F-43m was synthesized as a new compound under 6 GPa, which decomposed to the Mg and Mg_2Ni phases at 545 K as exothermic reaction. In Mg-Cu system, two new compounds such as the MgCu compound which has CsCl-type structure and Mg_<51>Cu_<20> compound belonging to space group Immm, were synthesized at 1073 K for 8 h under 6 GPa. The MgCu compound decomposed to the Mg_2Cu and MgCu_2 phases at 500 K and Mg_<51>Cu_<20> compound did to the Mg and Mg_2Cu phases at 430 K, respectively