Polymer-based hydrogen storage materials.

Lead Research Organisation: University of Manchester
Department Name: Chemistry


This multidisciplinary research programme seeks to overcome one of the most urgent and difficult challenges in materials science: hydrogen storage. In the context of climate change and dwindling oil reserves, hydrogen could be the perfect zero-carbon fuel for a car as it only gives water as a by-product. Although the method of production of hydrogen has yet to be optimised for sustainability, the greatest obstacle to the development of hydrogen-powered cars is the lack of a system for safe, efficient and convenient on-board storage of hydrogen. The physisorption of hydrogen on the large and accessible surface of a microporous material offers the attractive possibility of safe hydrogen storage with an energy efficient release for consumption. However, physisorption relies on the very weak interactions between the microporous material and hydrogen molecules, therefore, the mass loadings are generally low. The International Energy Authority (IEA) has set a target of 5% reversible mass loading for a realistic storage system. Thus, the challenge is set to make a microporous material of appropriate structure and chemical composition to help reach this ambitious target. Previously, polymers have not been investigated as materials for the storage of hydrogen because most polymers have enough conformational and rotational freedom to pack space efficiently and are therefore not microporous. However, our recently developed polymers of intrinsic microporosity (PIMs) do possess significant microporosity and preliminary hydrogen sorption results are encouraging with significant quantities adsorbed. Most importantly, the chemical composition of PIMs can be tailored via synthetic chemistry. Therefore, the adventurous primary objective of this proposal is to prepare novel PIMs in a form that demonstrate hydrogen loadings equal to or in excess of the IEA 5% benchmark at moderate pressures and 77 K.


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Description The main focus of the research was the synthesis, characterization and assessment of triptycene-based network Polymers of Intrinsic Microporosity (Trip-PIMs). It was found that the hydrogen adsorption of these materials can be controlled by the length and branching of the alkyl chains attached to the bridgehead position of the triptycene units so that the apparent BET surface area of the materials can be tuned within the range 618-1760 m2/g. Shorter (e.g. methyl) or branched (e.g. i-propyl) alkyl chains provide the materials of greatest microporosity, whereas longer alkyl chains appear to block the microporosity created by the rigid organic framework. The enhanced microporosity, in comparison to other PIMs, originates from the macromolecular shape of the framework, as dictated by the triptycene units, which helps to reduce intermolecular contact between the extended planar struts of the rigid framework and thus reduces the efficiency of packing within the solid. The hydrogen adsorption capacities of the triptycene-based PIMs with either methyl or i-propyl substituents are amongst the highest for purely organic materials at low or moderate pressures (1.83% by mass at 1 bar/77K; 3.4% by mass at 18 bar/77 K, saturation estimated at 5.2%). The impressive hydrogen adsorption capacity of these materials is related to a high concentration of sub-nanometre micropores, as suggested in the original grant application. The challenge still remains to enhance the microporosity of PIMs whilst retaining the sub-nanometre pore structure and increasing the heat of adsorption so that greater hydrogen storage at higher temperatures becomes feasible.
Exploitation Route Since this grant was completed, PIMs technology has been licensed to an international company in another application area.
Sectors Chemicals,Energy,Transport

Description This research has contributed indirectly to our efforts to develop commercial applications of polymers of intrinsic microporosity (PIMs). The first commercial product utilising a PIM, under license from the University of Manchester, is a 3M service life indicator for organic vapour cartridges, used in personal protection.
First Year Of Impact 2014
Sector Chemicals
Impact Types Economic