| The classification, features and development situation of hydrogen storage materials were reviewed in this thesis, with emphasis on the research evolution of light metal complex hydrides represented by Li BH4. For the purpose to prompt the development of Li BH4 hydrogen storage material, several composites based on Li BH4, x Li BH4/Mg-Y-Ni hydrides, y Li BH4/Mg-CeNi(Al) hydride and 4Li BH4-Li Al H4-Mg F2, were constructed. The hydrogen storage properties and de-/hydriding reaction mechanism of these composites were characterized by means of Sievert method, X–ray diffraction(XRD), fourier transform infrared spectroscopy(FTIR) and differential scanning calorimetry(DSC).The research of Mg-Y-Ni alloys indicates that the major phase of Mg YNi2.5 alloy is Mg YNi4, and that Mg4 YNi and Mg10 YNi are composed of Mg, Mg2 Ni and Mg Y2Ni2 phases. After full hydriding, the Mg-Y-Ni alloys transformed into Mg H2, Mg2 Ni H4, YH2 and YH3. The results of the hydrogen storage properties for x Li BH4/Mg-Y-Ni hydrides composites prepared by ball-milling show that the ending dehydriding temperatures of 6Li BH4-Mg YNi2.5, 12 Li BH4-2.5Mg4 YNi and 12 Li BH4-2.5Mg10 YNi composites are 510, 470 and 430 oC, respectively. The 12 Li BH4-2.5Mg10 YNi composite has the best dehydriding property with two dehydriding steps. The first step processed in the temperature range of 250~350 oC with 4.0 wt.% of hydrogen desorbed. The second step started around 350 oC and processed almost completely at 430 oC, desorbing 2.6 wt.% of hydrogen. The dehydriding reaction mechanism of 12 Li BH4-2.5Mg10 YNi composite was revealed by XRD and FTIR analysis. Firstly, Mg H2 and Mg2 Ni H4 dehydrogenated to form Mg and Mg2 Ni, and then Mg2 Ni reacted with Li BH4 to form Mg Ni2.5B2, and YH2 or YH3 reacted with Li BH4 to form YB4. The rehydriding amount of 12 Li BH4-2.5Mg10 YNi composite at 450 oC and 9 MPa is 5.3 wt.%. The investigations on the rehydriding mechanism of 12 Li BH4-2.5Mg10 YNi composite show that Mg absorbed hydrogen to generate Mg H2, and Mg Ni2.5B2 and YB4 reacted with Li H to form Li BH4, Mg2 Ni H4 and YH3.The different component of Mg-Ce-Ni(Al) alloys competely hydrogenated and Li BH4 were composited. It is indicated that the 17 Li BH4-2.5Mg11 Ce Ni composite has the best dehydriding property with 6.8 wt.% of hydrogen desorbed. The dehydriding process of 17 Li BH4-2.5Mg11 Ce Ni composite consists of two steps. The first step processed in the temperature range of 250~340 oC with 3.7 wt.% of hydrogen desorbed. The second step started around 340 oC and processed almost completely at 420 oC, desorbing 3.1 wt.% of hydrogen. The research of dehydriding reaction mechanism for 17 Li BH4-2.5Mg11 Ce Ni composite show that Mg H2 and Mg2 Ni H4 dehydrogenated to form Mg and Mg2 Ni, and then Mg2 Ni reacted with Li BH4 to form Mg Ni2.5B2, and Ce H2 reacted with Li BH4 to form YB4. The rehydriding property of 17 Li BH4-2.5Mg11 Ce Ni composite at 350~450 oC were studied. The results show that the composite has the best rehydriding property at 400 oC with 4.0 wt.% of hydrogen absorbed. The results of investigations on the rehydriding mechanism for 17 Li BH4-2.5Mg11 Ce Ni composite show that Mg absorbed hydrogen to generate Mg H2, and Mg Ni2.5B2 and Ce B6 reacted with Li H to form Li BH4, Mg2 Ni H4 and Ce H2.The de-/hydriding properties and reaction mechanism of 4Li BH4-Li Al H4-Mg F2 composite system was investigated. It is indicated that the composite system started to dehydrogenate at 100 oC, and processes almost completely at about 480 oC with a dehydrogenation amount of 9.0 wt.%. The research on the dehydriding mechanism shows that Li Al H4 decomposed to form Li H and Al with the catalysis of Mg F2, and then part of Mg F2 and Al reacted with Li H to form Al3Mg2 and Li F, the generated Al3Mg2 reacted with Li BH4 to form Al Mg B4, Al and Li H, Al continued to react with the residual Mg F2 and finally transformed to Al Mg B4、Li H and Li F competely. The investigations on the hydriding mechanism of 4Li BH4-Li Al H4-Mg F2 composite system show that Al Mg B4, Al and Li H could absorb hydrogen to form Al3Mg2 and Li BH4, and then part of Al3Mg2 absorbed hydrogen to generate Mg H2 and Al, the residual reacted with Li F to form Mg F2 and Al. The third-step dehydrogenation of 4Li BH4-Li Al H4-Mg F2 is 131 k J/mol, which is lower than that of the pristine Li BH4. |
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