• Holyfield, Leighton
• Diaz, Antonio Jose Noguera
• Bennet, Jack
• Burrows, Andrew D.
• Mays, Timothy J.
• Weatherby, Nick
• Dawson, Robert

Abstract

Due to its ability to be synthesised and used in a manner that does not produce CO2, hydrogen has gathered much attention as a sustainable energy vector. However, because elemental hydrogen has a very low volumetric energy density at standard temperature and pressure, it must be densified in order to be stored effectively, which has proven to be a difficult technical challenge. The current industrial state of the art for hydrogen storage is compression, whereby hydrogen is pressurised up to 70 MPa and stored in a carbon fibre reinforced polymer tank with an interior liner, made either of aluminium or a polymer. Compression has a number of flaws, including: a high energy penalty of compression; the high cost of the materials required to contain the pressure whilst maintaining a low tank mass; and an inherent safety risk. An alternative solution is the use of adsorption, a technique that uses the physical interaction between gas molecules and the solid surfaces of nanoporous materials to densify the hydrogen molecules.<br/>This work focuses mainly on two microporous adsorbents: the polymer of intrinsic microporosity PIM-1; and metal organic framework MOF-5. PIMs are polymeric materials composed of molecular chains that feature regular spiro-centres and rigid linkers, which cannot pack efficiently and leave free volume within their structures. PIM-1 is a bright yellow polymer that is soluble in polar aprotic solvents such as chloroform and THF, and forms robust, flexible films upon solvent casting, making it a highly attractive adsorbent [1]. However, PIM-1 films often show relatively disappointing BET surface areas of ~ 600 m2 g-1 in 77 K nitrogen isotherm tests [1], and this needs to be raised if the material could possibly be used to create a system that meets the United States Department of Energy targets for hydrogen storage [2]. This can be done by combining PIM-1 with another material, in this case the high surface area (~3000 m2 g-1) MOF-5, which has been the subject of industrial attention for solid-state hydrogen storage systems [3].<br/>This work aims to synthesise both PIM-1 and MOF-5 separately, before combining them into composite materials. Characterisation is performed on all the aforementioned materials, mainly through adsorption isotherms of nitrogen (77 K, 0 – 0.1 MPa), CO2 (273 K, 0 – 2 MPa) and H2 (77 K, 0 – 20 MPa). He pycnometry and thermogravimetric analysis is also performed. The materials made are compared using this data, and any relationships noted are presented.<br/>References:<br/> [1] Budd PM, Elabas ES, Ghanem BS, Makhseed S, McKeown NB, Msayib KJ, et al. Solution-Processed, Organophilic Membrane Derived from a Polymer of Intrinsic Microporosity. Adv Mater 2004;16:456–9.<br/>[2] U.S. Department of Energy. Target Explanation Document: Onboard Hydrogen Storage for Light-Duty Fuel Cell Vehicles, U.S. DRIVE; 2015.<br/>[3] Veenstra M, Yang J, Xu C, Purewal J, Gaab M, Arnold L, et al. Ford/BASF-SE/UM Activities in Support of the Hydrogen Storage Engineering Center of Excellence. 2015 DOE Annual Merit Review Proceedings, 2015<br/>

Topics

• density
• impedance spectroscopy
• surface
• polymer
• Carbon
• energy density
• aluminium
• Nitrogen
• composite
• Hydrogen
• thermogravimetry
• solvent casting
• casting