As societies depart from current economic models which are built around affordable and easily accessible fossil fuels to energy systems increasingly based on the use of renewable energies, the need grows for a wide-scale clean and sustainable energy vector. Hydrogen fulfils most of the needed equirements, but implementation and large scale penetration, especially for mobile applications, is precluded by technical issues. Among these, arguably the most complex is how to safely, economically and efficiently store hydrogen. Storage in a porous material offers some attractive features, which include fast kinetics, reversibility and moderate energy penalties. A new methodology to analyse hydrogen adsorption isotherms in microporous materials is presented in this thesis. The methodology is applied to hydrogen adsorption in different classes of high-surface area materials but could in principle be used for any supercritical fluid adsorbed onto a microporous material. To illustrate the application of the methodology, high-pressure hydrogen adsorption isotherms of four different materials were analysed, metal-organic frameworks MIL-101 and NOTT-101 and carbons AX-21 and TE7. The analysis extracts important information on the adsorptive capacities of the materials and compares them with conventional storage methods, which include compression, liquefaction and cryogenic compression. The methodology also aids in the calculation of the thermodynamics of adsorption,providing a more accurate calculation method than currently reported techniques, demonstrated with the calculation of the differential isosteric enthalpies for metal-organic framework NOTT-101.NMR and INS are used in a novel way at the same operating conditions of sorption experiments to validate the findings of the analysis. Both methods provide a qualitative validation for the analysis. Remarkably, the INS reveals that the adsorbed hydrogen in TE7 is in a solid-like state. GCMC simulations were also used to compare with the application and findings of the methodology, using silicalite-1 as a test material.
|Date of Award||26 Jun 2013|
|Sponsors||Engineering and Physical Sciences Research Council|
|Supervisor||Tim Mays (Supervisor)|
- hydrogen storage
- porous materials