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DFT study of 1,3-dimethylimidazolium tetrafluoroborate on Al and Cu(111) surfaces

Journal of Physical Chemistry C, ISSN: 1932-7447, Vol: 115, Issue: 30, Page: 14718-14730
2011
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Metrics Details

  • Citations
    17
    • Citation Indexes
      17
  • Captures
    26

Article Description

We present density functional theory results of the ionic liquid 1,3-dimethylimidazolium tetrafluoroborate ([mmim][BF]) adsorbed on Al and Cu(111) surfaces. Results comprise both relaxed configurations and constrained ab initio molecular dynamics simulations of up to 444 atoms for 19 ps. Relaxation results show that for submonolayer coverage many aspects of adsorption energies, electron transfer, and bond length variation can be explained from a simple bond saturation picture. The ions have a relatively weak energetic preference to interact with each other over interacting with the surface. Electron density accumulation and bond length changes in the [mmim ] ion are mostly independent of what the ion interacts with. In many cases, the shape of the surface on which a [mmim][BF] pair is situated is also of little importance. At submonolayer coverage, [BF ] ions have a stronger interaction with Al and Cu surfaces than [mmim] ions do, and as a result the latter have greater mobility on the surface. When [mmim][BF] pairs move across an Al surface, the migration energy is determined mainly by how close the [BF] ion can nestle itself against the surface. On Cu this is not the case because [BF] interacts less strongly with the surface than on Al. Both on Al and Cu, the energy required to move a [mmim][BF] pair across the surface is low. Molecular dynamics results show that while relaxation results can be useful in understanding some aspects of the behavior of ionic liquids on surfaces there are clear limitations to their usefulness. Even in low-temperature dynamics simulations, [mmim ] ions on Al spend much of their time in positions very different from their energy minima. At low coverage, this leads to a relative [BF ] enrichment that suggests some degree of anion-cation layering at the Al surface. Simulations with more [mmim][BF] pairs did not provide extra evidence for layering, as at greater coverage the [mmim][BF] dewetted from the surface to form a tiny droplet. The dewetting and layering results from molecular dynamics simulations provide possibilities for experimental verification. © 2011 American Chemical Society.

Bibliographic Details

T. P. C. Klaver; M. Luppi; M. H. F. Sluiter; M. C. Kroon; B. J. Thijsse

American Chemical Society (ACS)

Materials Science; Energy; Chemistry

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