Nanostructure confinement of ammonia borane within porous silica and carbon for hydrogen storage

Lu, Tao (2010) Nanostructure confinement of ammonia borane within porous silica and carbon for hydrogen storage. PhD thesis, James Cook University.

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Abstract

The development of hydrogen storage systems remains a grand technical challenge. The key issue is to find and synthesize materials with required physicochemical properties for hydrogen storage. Ammonia borane (AB) is considered to be one of the most promising candidates for a chemical method as it contains remarkable hydrogen content and is stable under normal storage conditions. This thesis focuses on synthesizing porous silica and carbon as nanoporous scaffolds for encapsulating AB and investigating the thermal decomposition performance of AB in the scaffolds with tunable pore structures and compositions.

A systematical investigation has been carried out on the influence of trifluoroacetic acid, acetic acid and their salts on the synthesis of helical mesoporous materials in the presence of a cationic surfactant cetyltrimethylammonium bromide (CTAB) as a template. Results show that helical mesostructures can be successfully synthesized when CF₃COO⁻ anions were used as additives with an additive/CATB molar ratio (R) range of 0.1-0.375 for the CF₃COOH/CTAB templating system and a relatively wider R range of 0.1-0.5 for the CF₃COONa/CTAB templating system. Our synthesis strategy can be used for the fabrication of helical mesostructured porous materials with adjustable pore and helical pitch sizes.

The influence of the time of 1,3,5-trimethylbenzene (TMB) addition on the self-assembled organic/inorganic composite structures in a nonionic block copolymer templating system has been investigated. By controlling the time at which TMB is added to the system, an evolution from multilamellar vesicle to ordered hexagonal mesostructure has been observed, providing a simple and novel approach for the synthesis of self-assembled porous silica materials with adjustable structures and tunable pore sizes.

In the development of porous carbon materials, a sol-gel polymerization induced colloid aggregation method is adopted with the use of a commercial polymeric melamine formaldehyde resin as nitrogen doped carbon precursor. The results show that the microstructure of porous carbon materials can be adjusted by polymerization of precursors and interposition of silica particles as a hard template. Moreover, the nitrogen content and functionality make the surface properties of the porous carbon unique and different from pure carbon materials. The presence of appropriate nitrogen functionalities can improve their behaviours and extend the application of porous carbon materials, such as electrode materials for double layer capacitors and catalytic materials for proton exchange membrane fuel cells.

The thermal decomposition behaviour of AB confined in nanoporous scaffolds with controlled pore structures and wall compositions is investigated. The nanoporous scaffolds tested include Silica-1 with a helical structure and a pore diameter of 1.8nm, Silica-2 with a vesicular structure and a pore diameter of 18 nm, as well as a macroporous N-doped carbon sample synthesized using 250 nm silica particles as a hard template. It is shown that in the case of Silica-1 with a small pore diameter of 1.8 nm, AB cannot be efficiently impregnated into the nanopores and the thermal decomposition of AB is associated with the formation of volatile by-products. For Silica-2 with a large pore diameter of 18 nm, it is a relatively better candidate compared to small pore Silica-1 because the formation of most by-products is suppressed and the first hydrogen desorption peak is lowered by 13 °C compared to neat AB. However, a small amount of released ammonia is still observed. In the case of the macroporous N-doped carbon material, the total amount of hydrogen released is 6 wt%, while the formation of both ammonia and borazine are suppressed. More importantly, the first release peak of hydrogen is 90 °C, about 20 °C lower than that of neat AB, which is better than a pure carbon material CMK-3 and equivalent to a Li-CMK-3 material reported in the literature. Our results have shown that in addition to the influence of pore size, the composition of the host material is another important factor. It is anticipated that highly porous N-doped carbon materials with further optimized pore parameters will be ideal candidates for AB immobilization and hydrogen storage.

Item ID: 39163
Item Type: Thesis (PhD)
Keywords: acetic acid; energy; H2; hydrogen storage; mesoporous materials; nanomaterials; nanostructures; porous material; trifluoroacetic acid
Additional Information:

Publications arising from this thesis are available from the Related URLs field. The publications are:

Lu, Tao, Yao, Xiangdong, Lu, Max Gao Qing, and He, Yinghe (2010) Roles of trifluoroacetic acid, acetic acid and their salts in the synthesis of helical mesoporous materials. Journal of Porous Materials, 17 (1). pp. 123-131.

Lu, Tao, Yao, Xiangdong, Lu, Gao Qing, and He, Yinghe (2009) Controlled evolution from multilamellar vesicles to hexagonal mesostructures through the addition of 1,3,5-trimethylbenzene. Journal of Colloid and Interface Science, 336 (1). pp. 368-373.

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Date Deposited: 05 Aug 2015 23:17
FoR Codes: 09 ENGINEERING > 0912 Materials Engineering > 091205 Functional Materials @ 33%
10 TECHNOLOGY > 1007 Nanotechnology > 100708 Nanomaterials @ 33%
10 TECHNOLOGY > 1007 Nanotechnology > 100712 Nanoscale Characterisation @ 34%
SEO Codes: 85 ENERGY > 8506 Energy Storage, Distribution and Supply > 850606 Hydrogen Storage @ 100%
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