Post-synthetic modifications of metal-organic frameworks for H2 storage
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  • Post-synthetic modifications of metal-organic frameworks for H2 storage

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With increasing demands on fossil fuels, many industrialised nations are turning towards alternative sources of energy. The “hydrogen economy”, in which hydrogen is used as a “green” feedstock in fuel cells to power motor vehicles, homes, etc. has been highlighted as a potential solution to the energy problem. Challenges to be faced before this becomes a reality include the development of sustainable and fossil-free methods of hydrogen production, the safe and reversible storage and transport of hydrogen, development of affordable hydrogen fuel cell, as well as the development of efficient and reliable hydrogen sensors. [1]

Among these issues hydrogen storage is arguably the biggest challenge in developing a hydrogen economy. While different types of materials are being explored as hydrogen carriers, porous materials have the advantage of offering fast kinetics for hydrogen sorption as well as reversibility over multiple cycles. Among them, metal-organic frameworks (MOFs) are being increasingly considered as promising materials for non-dissociative hydrogen adsorption. They are organic-inorganic hybrid materials displaying high crystallinity as well as high and regular porosity. In addition, their syntheses can be carried out under mild conditions, allowing for their rational design and facile pre- or post-synthetic modification. [2]

While some MOFs display extraordinarily high hydrogen uptake, this, due to the low enthalpy of adsorption, occurs at cryogenic temperatures and high pressures; a serious drawback for application. Several ways have been identified leading to enhanced hydrogen-storage properties in metal-organic frameworks, via two major mechanisms: i) increase of the isosteric heat of adsorption or ii) increase of the surface area and pore volume. [3]

In this talk I will present our recent advances on post-synthetic modification of selected MOFs in order to enhance their hydrogen-storage properties. The modifications involve a number of strategies, such as solvent-assisted linker exchange, surface modification, addition of metal ions on the linker side and addition of metal nanoparticles. Although in some cases we obtained an impressive hydrogen-uptake enhancement at ambient temperature (up to 100%), this beneficial effect was not observed at high loadings (cryogenic temperatures). Possible reasons for the hydrogen-uptake enhancement as well as the potential benefits will also be discussed.

 

[1] D. P. Broom, Hydrogen Storage Materials, The Characterisation of Their Storage Properties, Springer Verlag (2011)

[2] J. Sculley, D. Yuan and H.-C. Zhou, Energy Environ Sci. 2011, 4, 2721

[3] M. P. Suh, H. J. Park, T. K. Prasad and D.-W. Lim, Chem. Rev. 2012, 112, 782