The research project described in the thesis uses atomic-scale computational modelling to investigate the storage of hydrogen in graphite intercalate compounds (GICs). The work is relevant to the energy economy, as hydrogen is a source of clean energy, and can be used efficiently in fuel cells to generate electricity. Storing hydrogen safely has long been a challenge in materials science and, since the proposal of a hydrogen-based transport economy, has attracted great attention. Graphite intercalate compounds offer the possibility of dense storage, because they contain large absorption pores for hydrogen to bind. The absorption mechanisms and patterns in different intercalate compounds are not well understood, and this is the motivation for this work. Alkali and alkaline-earth metal GICs (A/AE-GICs) were modelled using density func- tional theory (and benchmarked with quantum chemistry) to investigate their hydrogen storage capabilities and their stability against decomposition into the metal hydride and pure graphite upon hydrogenation. Detailed studies of the calcium-GIC were per- formed and also a survey of the other A/AE-GICs. The effect of the commonly modelled MC14 GIC compared with the experimental MC12 stoichiometry has been investigated to bridge the gap between experiment and theory. The calcium-GIC was found to favourably absorb hydrogen within U.S. Department of Energy targets, but was found to be extremely unstable. Our investigations showed that all AE-GICs are unstable. Heavier A-GICs were found to stably absorb hydrogen at reasonable volumetric densities at the cost of gravimetric densities. The theoreti- cally modelled MC14 stoichiometry was found to be fundamentally different from the experimental MC12 stoichiometry, with the latter breaking the simple symmetry of the former and offering many more distinct absorption sites and barriers to diffusion. Pair potentials have been built and parametrised to KC14 to aid simple modelling of KCn GICs in, for example, classical molecular dynamics.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:626284 |
| Date | January 2013 |
| Creators | Wood, C. R. |
| Publisher | University College London (University of London) |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://discovery.ucl.ac.uk/1399843/ |
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