Boron-carbon-nitrogen heterocycles for hydrogen storage: Synthesis and characterizations

The implementation of hydrogen economy is suffering from several unresolved problems with one particular challenge being the storage of appropriate amounts of hydrogen in a safe and efficient manner. Among the current hydrogen carriers, BN based compounds exhibit excellent volumetric and gravimetric storage capacity, but they still suffer from various drawbacks. In my project, I reported the first synthesis and characterization of 1,6;2,3-bis-BN cyclohexane, an isostere of cyclohexane with two adjacent BN pairs. This compound exhibits an appealing hydrogen storage capability of >9.0 wt%, nearly twice as much as the 1,2;4,5-bis-BN cyclohexane. Other cyclic BCN compounds, including BN-substituted decalin and 1,5;2,3-bis-BN cyclopentane, were designed, and efforts were made to prepare and isolate them. Chapter 1 reviews the current development of ammonia borane and boron-carbon-nitrogen containing molecules, especially from the perspective of hydrogen storage application. Existing challenges are put forward at the end of this chapter. Chapter 2 gives an overview of the instruments and technologies applied in my PhD project. Their corresponding parameters and operations are also described. The synthesis of the key compound, 1,6;2,3-bis BN cyclohexane, is described in Chapter 3. Isolation details and identification results such as NMR, single-crystal XRD and elemental analysis, are presented. The basic physical and chemical properties of this new compound are investigated, as well as its reactivities towards HCl and H₂O. Dehydrogenation of 1,6;2,3-bis BN cyclohexane is presented in Chapter 4. The hydrogen liberation methods include catalysed dehydrogenation in solvents and thermal dehydrogenation in solid phase. 1.47 eq. H₂ gas can be liberated from 1 eq. of 1,6;2,3-bis BN cyclohexane in the presence of Pd/C at RT. Under thermal activation, the gravimetric capability is > 9 wt%, which means 4 eq. H₂ is released from 1 eq. 1,6;2,3-bis BN cyclohexane. The thermal dehydrogenation pathway was studied via FTIR and NMR analyses. Finally, regeneration of spent BN materials was achieved via a three-step method. The early research work of preparation and isolation of BN-substituted decalin and 1,5;2,3-bis-BN cyclopentane are discussed in Chapter 5. The desired BN-substituted decalin could be possibly obtained 𝘷𝘪𝘢 a synthesis method starting from 1,6;2,3-bis-BN cyclohexane. A one-pot synthesis method showed possibility for the preparation of 1,5;2,3-bis-BN cyclopentane. They key achievement is summarized in Chapter 6. Covid outbreak has caused major disruption to my research so several interesting questions remained to be solved. Possible solutions to these questions are given in chapter 6.

Author dc:creator

• Dai, Yan

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• info:eu-repo/semantics/embargoedAccess
• The author owns the copyright in this thesis including all reproduction and reuse rights for the work. The work may not be altered without the permission of the copyright owner. Attribution is essential when quoting or paraphrasing from this thesis.
• au.edu.uts.lib/ppc
• © 2022 Yan Dai

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en_US

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http://hdl.handle.net/10453/169968

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oai:opus.lib.uts.edu.au:10453/169968