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The holey grail of hydrogen storage

已有 4583 次阅读 2007-12-4 21:38 |个人分类:能源环保导读

The holey grail of hydrogen storage


04 December 2007

A polymer riddled with tiny pores could lead to a novel hydrogen fuel tank, say chemists in the US.

The porous polymer material

Frantisek Svec of the Lawrence Berkeley National Laboratory and colleagues at the University of California, Berkeley, made the highly porous materials from polyaniline. Svec used hypercrosslinking to give a mesh-like material with a strong affinity for hydrogen, and a high surface area.

'Using hydrogen as a CO<sub>2</sub>-free fuel is a nice idea,' said Svec. But storing the gas is complicated as the gas is 'very difficult to compress or liquefy. One alternative is to store it in materials with a very high surface area.'

The Berkeley team made the new material by adding small molecular crosslinkers to polyaniline that had been swelled in solvent. These short, rigid crosslinks hold the polymer chains apart even when the solvent is removed, leaving a material full of nanometre-scale pores. The resulting mesh had a surface area eight times higher than the best previous porous polyaniline, and a high affinity for hydrogen.


"These short, rigid crosslinks hold the polymer chains apart even when the solvent is removed."
'The key advance with this work is the new approach to make porous polymers,' said Andrew Cooper, who studies hydrogen storage polymers at the University of Liverpool, UK. The materials are still far from practical hydrogen stores, Cooper added: 'With what you'd have to change in structure to achieve room temperature hydrogen storage, it's arguable whether you could still call it the same material.'

Svec agreed there is still a lot of work ahead. 'We need polyanilines with a much higher surface area - we need small pores, and a lot of them,' he said. The Berkeley team is currently trying different crosslinkers, and different reaction conditions, to increase the material's proportion of 1-2 nm pores.

James Mitchell Crow


Link to journal article

Hypercrosslinked polyanilines with nanoporous structure and high surface area: potential adsorbents for hydrogen storage
Jonathan Germain, Jean M. J. Fréchet and Frantisek Svec, J. Mater. Chem., 2007, 17, 4989
DOI: 10.1039/b711509a


Paper

J. Mater. Chem., 2007, 17, 4989 - 4997, DOI: 10.1039/b711509a


Hypercrosslinked polyanilines with nanoporous structure and high surface area: potential adsorbents for hydrogen storage

Jonathan Germain, Jean M. J. Fréchet and Frantisek Svec


A method for the preparation of an entirely new type of nanoporous material, hypercrosslinked polyaniline, with permanent porous structure and specific surface areas exceeding 630 m2 g–1 has been developed. The hypercrosslinking reaction was carried out with commercial polyaniline and diiodoalkanes or paraformaldehyde using both conventional and microwave assisted processes. Polyaniline swollen in an organic solvent was hypercrosslinked to form a rigid, mesh-like structure with permanent porosity and a high surface area. The resulting materials were characterized using infrared spectroscopy and elemental analysis. Porous properties were determined by means of scanning electron microscopy as well as nitrogen and hydrogen adsorption. Short crosslinks such as those formed using paraformaldehyde and diiodomethane led to materials with the highest surface areas. Surface area also increased with the concentration of polyaniline in solution used during preparation. The hydrogen storage capacities of these materials were also tested and a capacity of 2.2 wt% at 77 K and 3.0 MPa was found for the best adsorbent. Hypercrosslinked polyanilines exhibit a remarkably high affinity for hydrogen, which results in enthalpies of adsorption as high as 9.3 kJ mol–1 (exothermic), in sharp contrast with hypercrosslinked polystyrenes and metal–organic frameworks for which significantly lower enthalpies of adsorption, typically in the range of 4–7 kJ mol–1, are measured.

Graphical abstract image for this article  (ID: b711509a)


Fig. 1 Schematic representation of the hypercrosslinking process. First, distance is created between polymer chains via swelling or dissolution in a solvent. Second, the polymer is crosslinked in its swollen state. Finally, the solvent is removed while rigid crosslinks keep the polymer chains separated, resulting in a material with permanent porosity.
Scheme 1 Simplified reaction schemes showing the preparation of hypercrosslinked polyaniline using single step crosslinking with diiodoalkanes (A), dimethylsulfoxide-assisted two-step crosslinking with diiodomethane (B) and crosslinking with paraformaldehyde (C).

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来自http://www.rsc.org


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