| Recently, ammonia-borane (NH3BH3, AB) as a typical chemical hydride system has received great attention as a promising hydrogen storage candidate, because of its large hydrogen content of19.6wt.%and relatively low hydrogen desorption temperature. In this thesis, the influence of nanocofinement on the dehydrogenation properties of ammonia-borane was investigated through incorporation of it into nano-scale templates and electrospinning techniques. Furthermore, a series of derivatives of ammonia-borane were synthesized by modifying its structure. The main results are as below:(1) The ammonia-borane (AB, NH3BH3) modified with platinum nanoparticle functionalized carbon nanotubes (CNTs)(Pt@CNTs) was prepared through a new "ammonia-deliquescence" method. It has been demonstrated that the synergetic catalysis of CNTs and platinum nanoparticles, and the nanoconfinement of AB are two crucial factors in enhancing the dehydrogenation of AB. Both CNTs and platinum nanoparticles showed favorable catalytic activities towards the thermolysis of AB, which not only depressed the emission of the poisonous by-product borazine, but also prevented severe material foaming and expansion during the decomposition. Furthermore, the nanoconfinement of AB through the "ammonia-deliquescence" method also led to enhanced dehydrogenation kinetics.(2) According to the results of the nanoconfinement of AB above, we tried to prepare PVP/AB nanofibers through electrospinning techniques, because this kind of method could decrease the size of AB particles to nano-scale. The AB nanofibers prepared shows significant improvements in dehydrogenation kinetics and complete suppression of boracic byproducts. However, the evolution of ammonia can not be suppressed, and which is shifted to low temperature. To depress the evolution of ammonia, MgCl2was doped in the PVP/AB nanofibers system and pure hydrogen release was relized successfully.(3) In order to further understand the mechanism of AB upon thermal decomposition in the presence of polymers, we chose another polymer (polyacrylamide, PAM) to blend with AB. The prepared samples (AB@PAM) showed similar dehydrogenation properties as the PVP/AB nanofibers.It was demonstrated that the enhanced kinetics may owe to the refinement of crystal particles and disruption of the dihydrogen bonding network of AB after blending, while the entire suppress of boracic impurities and the evolution of ammonia may be due to the interaction between O in the carbonyl groups (C=O) of PAM and B in the AB molecules, which weakens the B-N bonds to release NH3and subsequently forms B-O bonds to inhibit the emission of boracic impurities. Finally, metal chlorides (CaCl2, MgCl2and ZnCl2were introduced to the AB@PAM, which leads to a significant depress of NH3evolution, thereby enabling the dehydrogenation of the polymeric composite to occur at low temperature with enhanced hydrogen purity.(4) Finally, we synthesized two novel N, N’-phenyl substituted derivatives of [NH4]+[BH4]-(m/p-BABB) and three linear C-N-B materials (DETAB, TETAB and TEPAB). The m/p-BABB exhibited high stability compared to pure [NH4]+[BH4]-, and they start to release H2at about50℃with the evolution of a small amount of B2H6during their decmposition. Furthermore, the three linear C-N-B materials also exhibited favorable dehydrogenation properties; with the onset H2-release temperature of about60℃, and release of pure H2without any impurities upon their decomposition. The introduction of organic groups is expected to disrupt the dihydrogen bonding network and lower their activation energy for hydrogen release compared to the NH3BH3. |
PDF Full Text Request