| Storage of hydrogen is one of the important factors that restrict the wide utilization of hydrogen. The development of high efficient and safe hydrogen storage technique is necessary.In this thesis, the category and characteristics of solid-state hydrogen storage materials were introduced. Moreover, the research progress and existing problems of complex hydride,especially LiBH4, were reviewed. For the purpose of decreasing dehydrogenation temperature and improving rehydrogenation property of LiBH4, YF3, CaC2 and YbAl hydride were selected to combine with LiBH4 based on the method of reactive destabilization. The hydrogen storage properties of the composite system were characterized by the Sievert's method. In addition, the de-/hydrogenation reaction mechanisms were analyzed by means of X-ray diffraction?XRD?,Fourier transform infrared spectroscopy?FTIR?, scanning electron microscope?SEM?, energy dispersive spectroscope?EDS? and X-ray photoelectron spectroscopy?XPS?.The dehydrogenation mechanism of 3LiBH4/YF3 system was firstly studied. It was found that there are two dehydrogenation plateaus in the pressure-composition-temperature?p-c-T?curve in the range of 010 MPa at 320340 °C. The hydrogen pressures of these two dehydrogenation plateaus are both much higher than that of pristine LiBH4. The dehydrogenation process for the 3LiBH4/YF3 system origins from the derect reaction between LiBH4 and YF3, and can be devided into two stages. The higher-plateau dehydrogention reaction can be indicates as LiBH4 + YF3 ? 3/4Li YF4+ 1/4YB4 + 1/4Li H + 15/8H2, and the lower-plateau dehydrogention reaction can be expressed as 3/4Li YF4+ 1/4Li H + 2LiBH4?1/2YB4 + 1/4YH2 + 3Li F + 31/8H2. In comparison with pristine LiBH4, the increase of thermodynamic driving force and the self-catalyzing effection of dehydrogenation might be the main reasons for the decrease of dehydrogenation temperature for the 3LiBH4/YF3 system.Secondly, the 2LiBH4/Li Al H4/0.5CaC2 and 2LiBH4/Mg H2/0.5CaC2 systems were designed and investigated. The results show that the 2LiBH4/Li Al H4/0.5CaC2 system released hydrogen before 440 °C and the amount of hydrogen desorbed was about 6.6 wt.%. For the2 LiBH4/Mg H2/0.5CaC2 system, it quickly released hydrogen in the tempearature range of350430 °C, desorbing about 6.8 wt.% of hydrogen. The XRD and FTIR analysis show that CaC2 can change the reaction path and make the systems reactive destabilization, thus improving the hydrogen storage properties. The rehydrogenation amounts of2 LiBH4/Li Al H4/0.5CaC2 and 2LiBH4/Mg H2/0.5CaC2 systems at 450 °C and 9 MPa are 5.4 and6.7 wt.%, respectively.In order to obtain the YbAl hydride/4LiBH4 system, the hydrogenation property of YbAl alloy was investigated to completely hydrogenate the YbAl alloy. The results show that theYbAl alloy can not be hydrogenated completely under high temperature and high hydrogen pressure?400 ° C, 8 MPa H2? for about 20 h. The hydrogenation reaction of YbAl2 phase in the YbAl alloy can be expressed as 12 YbAl2 + 5H2 ? 8YbAl3 + 4YbH2.5. But the YbAl alloy can be completely hydrogenated by ball milling under 4 MPa H2 for 10 h, and the hydrogenation reaction for YbAl2 was 4YbAl2+ 5H2 ? 4YbH2.5+ 8Al.The completely hydrogenated YbAl alloy was combined with LiBH4. It was indicated that the YbAl hydride/4LiBH4 system starts to release hydride at about 170 °C, and quickly desorbed hydrogen at about 408 oC. The total dehydrogenation amount is about 4.8 wt.%. The YbAl hydride/4LiBH4 system can reabsorbing 4.2 wt.% of hydrogen at 450 °C and 9 MPa,exhibiting a betten rehydrogenation ability. |
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