Synthesis Of Metal Hydrogen Storage Composite

On world, the research on hydrogen storage alloys is relatively ample and perfect, and in some scopes have got certain level applications (such as in Ni-MH battery etc.). But the hydrogen capacity of the metal hydriding is generally low, the reversible circulating performances and reaction conditions are still un-perfect. The research on the carbon-system hydrogen storage materials (such as graphite, carbon nano-tube, carbon nano-fiber etc.) start near though, its hydrogen capacity far exceed to the metal hydriding is accepted by all.This paper is a basic application research of hydrogen storage materials. The research bases on the comparison of hydrogen storage alloys and carbon-system hydrogen storage materials, and combined them together to synthesis a new kind of hydrogen storage composite. And its hydrogen storage characteristics also have been studied in this paper.In this paper, Mg-based hydrogen storage alloys (its hydrogen capacity is one of the highest among the hydrogen storage alloys) were selected to combine with the graphite to synthesis two new serials hydrogen storage composites by mechanical alloying. One is Mg87-xNi12MoGx (x=5, 10, 15, 20, 25. G represents graphite), the other is 2Mg-Ni-xMo-w%G (x=0.1, 0.2; w=5, 10, 20; G represents graphite). Among the two serial composites, Mg62Ni12MoG25 and 2MgNi-0.1Mo-10%G (synthesized under the conditions of 300r.min-1 and 40h grinding time) have been found have the most perfect performances. Compared with the previous hydrogen storage materials, their performances are more perfect in hydrogen capacity, absorption kinetics and thermodynamics. Show mainly in: 1. the reaction temperature dropped to 423K, far lower than other hydrogen storage alloys; 2. can directly absorb hydrogen without activation; the adsorption time is 100 min or so; 3. the hydrogen capacity of some composites reach to 6.22wt%; 4. have ideal platform pressure (about 0.5 MPa) and have ideal platform width. It has been considered that this cause mainly because of the synergetic interactions between magnesium and graphite. Graphite is characterized as having a polycondensed-ring structure whose carbon net is considered as an infinite array of aromatic molecules and accumulates vertically in the three-dimensional framework. During the course of grinding , there forms a new phase similar to the Laves phase between magnesium and graphite under the supplementary role of THF, thus the new composites can absorb hydrogen in large quantities. Ni and Mo in the composites maybe take the mainly roles of catalysis or regulate the adsorption and desorption performances of the composites. Additionally, grinding time and grinding speed have been found greatly affect the performances of the composite. As in the study of 2Mg-Ni-xMo-w%G (x=0.1, 0.2; w=5, 10, 20; G represents graphite), we can find, according to different grinding time and different grinding speed, the hydrogen capacities and P-c-T curves of the 2Mg-Ni-0.1Mo-10%G have been greatly changed. SEM and XRD have been applied to examine the microstructure of the new composites, and the storage principle has been expatiated from its micro-storage mechanism.