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Study on the Hydrogen Storage Properties of Complex Hydrides

Author: LiYongTao
Tutor: SunDaLin
School: Fudan University
Course: Physical Electronics
Keywords: Hydrogen Storage Coordination hydride Ordered Mesoporous Carbon An alkaline earth metal chloride, Nano constraints Catalytic doping Chemically modified
CLC: TG139.7
Type: PhD thesis
Year: 2011
Downloads: 207
Quote: 1
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Abstract

Hydrogen efficient, economic, security, storage / transport is a key link in hydrogen utilization. Chemical hydrogen storage because of its considerable technical advantages in storage density, to the efficiency and security concern. Ligand hydride hydrogen storage density with higher weight is one of the hot spots in the current chemical hydrogen storage materials research, but slow kinetics and poor reversibility restricted its practical application. The review coordinated hydride hydrogen storage materials research progress and its problems on the basis of select NaAlH4 NH3BH3 (AB) as the object of study, and do the work as follows: First, by building nano constraints system to improve NaAlH4 de / hydrogenation characteristics; Second, study the catalytic dehydrogenation of NaAlH4 system performance of nano-carbon materials; Finally, the use of chemically modified to improve AB's heat liberation hydrogen behavior. The specific content and conclusions are as follows: (1) to a pore size of about 4 nm ordered mesoporous carbon MC nano skeleton, melt impregnation prepared by the MC part of the constraint the NaAlH4 system (NaAlH4/MC). Namely the distribution in the the MC the outer surface of the crystalline NaAlH4 large particles with MC nanopore constraint nm or amorphous NaAlH4 coexistence. The thermal analysis results show that compared with the pure NaAlH4 NaAlH4/MC the thermal stability decreased significantly. Initial dehydrogenation temperature decreased from 220 ℃ to 150 ℃ the the full dehydrogenation temperature decreased from 320 ℃ to 210 ℃. De / the hydrogenation performance tests show that NaAlH4/MC reversible hydrogenation performance. 100 ~ 150 ℃ / 3.0 ~ 7.0 MPa H2, under relatively mild conditions can be achieved in the metal catalyst under conditions the further hydrogenation of the dehydrogenation product. The stripper / hydrogenation performance improvement is mainly attributed to a MC of nano constraints and chemical catalytic synergy, wherein nano constraints play a major role. (2) through the melt impregnation, the stripping / hydrogenation method of combining the further construction of the MC fully constrained the the NaAlH4 systems (Space-confined NaAlH4/MC). Part NaAlH4 its dehydrogenation product NaH and Al are fully constrained MC nanopore exist in the form of amorphous or fine crystalline, reversible and hydrogenation at 150 ° C, the 7 MPa milder conditions; while NaAlH4 distribution of another portion in the MC outer surface is removed by stripping / hydrotreating, i.e. its the dehydrogenation product NaHH and Al in the stripper / hydrogenation conditions do not participate in a reversible cycle. De / hydrogenation performance tests show that the MC completely constraints the NaAlH4 of cycling performance significantly enhanced. The capacity retention ratio after 15 cycles greater than 80%, much higher than the pure NaAlH4 by 50% after 5 cycles. EDS analysis further showed that the 2-3μm or of 8μm large particles grow into pure NaAlH4 dehydrogenation product of Al by 5 cycles, Space-confined NaAlH4/MC even after 15 cycles remains relatively uniform distribution of Al element. Analysis of MC nanopore as \barrier, so that NaAlH4 under milder conditions reversible cycle. (3) MC fully constrained NaAlH4 has excellent performance dehydrogenation kinetics. The isothermal dehydrogenation Test show that the dehydrogenation process of the Space-confined NaAlH4/MC no significant incubation period of the dehydrogenation capacity from 180 ° C within 90 min of pure NaAlH4 0.5wt.% To 5.0 wt%, and the reaction activation energy Ea 116 kJ / mol to 46kJ/mol. The dynamic model calculations show that NaAlH4 nano restraint system dehydrogenation process is divided into two stages: the first stage of growing up by the one-dimensional nucleation control, and the second stage by the three-dimensional phase boundary migration and proliferation of jointly controlled. (4) The dissolution - recrystallization prepared nano-carbon material load NaAlH4 system. Scanning electron microscopy revealed the graphene (Graphene) load sample NaAlH4 lamellar continuous body, load samples of fullerene (C60) NaAlH4 the petaloid particles of 5-10μm, whereas the MC load sample NaAlH4 of spherical particles of 1-3μm . Thermal analysis showed pure NaAlH4 220 ℃ dehydrogenation, Graphene, C60 and MC load NaAlH4 initial dehydrogenation temperature reduced to 190,185 and 160 ° C respectively. Further calculated by Kissinger equation shows that the with pure NaAlH4 dehydrogenation generation Na3AlH6, the three-step reaction of Na3AlH6 dehydrogenation to NaH NaH decomposition activation energy compared Graphene, C60 and MC load the NaAlH4 of the first step reaction activation were reduced by 13 19 and 40 kJ / mol, and the second reaction activation energy were reduced by 77,125 and 148 kJ / mol, the third step of the reaction activation energy, respectively, to reduce the 59,122 and 131 kJ / mol. The 27Al NMR spectral analysis showed that Al atoms of the local structure change, confirmed the presence of interactions between the nano-carbon material with NaAlH4, this may be caused NaAlH4 the lower the thermal stability and dynamic performance improvement reasons. The foregoing analysis available, the role of the law of the nano-carbon material on the of NaAlH4 dehydrogenation process MC gt; C60 gt; Graphene. (5) adding an alkaline earth metal chloride by mechanical milling method can significantly improve the AB valence bond liberation characteristics and thermal behavior of hydrogen. Compared with the pure AB, MgCl2/AB samples of BH and NH bond stretching vibration frequency was significantly offset, initial decomposition temperature decreases about 60 ℃ and NH3, B2H6, and N383H6-release. Further studies showed that the alkaline earth metal chloride has a similar role in the pyrolysis behavior of AB, but MgCl2 CaCl2 stronger than inhibit the the NH3 release of role. The analysts believe that the alkaline earth metal chloride AB double chemical modification effect, that Cl substitution H activation BH key and alkaline earth metal with AB molecular interactions activate the NH bond and the underlying causes of the lower dehydrogenation temperature and inhibit the release of impurity gases. The above results of ammonia boron alkyl compounds and boron hydride ammonia complex performance improvement has reference.

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