| Recently, metal complex hydrides have been widely studied around the world because they have merits of higher gravimetric and volumetric hydrogen storage density compared to traditional hydrogen storage alloys. However, most of metal complex hydrides also have disadvantages of high dehydrogenation temperature, bad dehydrogenation kinetics and difficulties in reversible operations, which limit the application in normal conditions.Based on the review of the research and development on B-based complex hydrides for the hydrogen storage materials in the world, the Li-Mg-B-H composite was selected as the study object of this work. The effects of niobium-based catalysts and different fluorides on the hydrogen storage properties of the composite were studied. The mechanism of dehydrogenation/rehydrogenation process of Li-Mg-B-H composite was investigated by means of XRD, TG/DSC/MS, FTIR, SEM/EDAX. And a new Li-Mg-Fe-B-H composite was first studied in this thesis.For 2LiBH4/MgH2 composite, the experimental results revealed that addition of 5mol.% different Niobium-based catalysts NbF5 had the most eminent effect on the hydrogen storage properties. The results indicated that F~ anion could dissolve in LiBH4 crystal lattice, and improve the dehydogenation kinetics.MgF2, CaF2, CeF3 were added into Li-Mg-B-H composite system as a reactant. The results showed that CeF3 had the best influence on hydrogen storage properties. This was ascribed to the following reasons:(1) CeB6 was formed during dehydrogenation process, and CeB6 and MgB2 alter the dehydrogenation pathway of LiBH4; (2) porous structure was formed for this composite, which enhanced the hydrogen diffusion and then improve the decomposition kinetics of LiBH4.Mg2FeH6 was synthesized by sintering MgH2 and Fe in the mole of 2:1 after ball milling, the maximum hydrogen desorption capacity reached 4.85 wt %. A new hydrogen storage composite was formed by composing Mg2FeH6 and LiBH4, and the maximum hydrogen desertion capacity reached 7.58wt.%. Key words: Hydrogen storage materials, Complex hydride, LiBH4, MgH2, Mg2FeH6... |
