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Shyue Ping Ong Gerbrand Ceder

Effect of Functional Groups on the Electron Affinities and Ionization Energies of Ionic Liquid Ions Using Quantum Chemistry Techniques. Shyue Ping Ong Gerbrand Ceder. Electrochemical Applications of Ionic Liquids. Large Space of Ion Structures. Base Ions. Functional Groups.

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Shyue Ping Ong Gerbrand Ceder

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  1. Effect of Functional Groups on the Electron Affinities and Ionization Energies of Ionic Liquid Ions Using Quantum Chemistry Techniques Shyue Ping Ong GerbrandCeder

  2. Electrochemical Applications of Ionic Liquids

  3. Large Space of Ion Structures Base Ions Functional Groups Over 200unique ions structures explored.

  4. Substitution Algorithm

  5. Electrochemical Windows of ILs Same cation, different anion, slightly different ECL Different cations, same anion, very different ECL Current density EW = EAL – ECL ECL (Cathodic Limit) Potential (V) vs Reference EAL (Anodic Limit) Ohno, H., (2005), Electrochemical Aspects of Ionic Liquids, Wiley-Interscience.

  6. Calculating Electrochemical Stability • True redox stability ??? Kroon, M. C.; Buijs, W.; Peters, C. J. & Witkamp, G. J. (2006), Green Chemistry 8(3), 241—245.

  7. Proxy Measures for True Redox Stability Koch, V. R.; Dominey, L. A.; Nanjundiah, C.; Ondrechen, M. J. J. Electrochem. Soc.1996, 143, 798–803. • Hypothesis : Vred & Vox correlated with electron affinity (EA) and ionization energy (IE) respectively • EAs and IEs can be computed efficiently and accurately using simple computational methods at relatively low cost

  8. Computational Methodology • Gaussian 03 Quantum Chemistry Package • Model Chemistry: B3LYP/6-311+G(2d,p)//B3LYP/6-31+G(D) • Thermal Gibbs Free Energy corrections obtained via Frequency Calculation (scaling factor : 0.9806) Scott, A. & Radom, L. (1996), JOURNAL OF PHYSICAL CHEMISTRY 100(41), 16502-16513.

  9. Vertical versus Adiabatic IE/EA Anions in general undergo a greater amount of geometric relaxation than cations Some cations, especially Imidazolium-based cations undergo a greater degree of geometric relaxation

  10. Relative Redox Stability of Cation Types Ohno, H. (2005), Electrochemical Aspects of Ionic Liquids, Wiley-Interscience.

  11. Effect of Alkylation on Cations Alkyl groups are electron-donating PYR1n3 -> PYR1n7 : −3.73V -> −3.89V Appetecchi, G. B.; Montanino, M.; Zane, D.; Carewska, M.; Alessandrini, F. & Passerini, S. (2009), ELECTROCHIMICA ACTA 54(4), 1325-1332.

  12. Effect of Substitution Position P. Bonhote, A. Dias, N. Papageorgiou, K. Kalyanasundaram and M. Gratzel, Inorg. Chem. 1996, 35, 1168-1178 Greatest of lowering of EA occurs for alkylation at C2 position - In agreement with experiments!

  13. Effect of Fluoroalkylation on Anions • No monotonic decreasing trend in IE with fluoroalkylation observed • Fluorine is the most electronegative element => great inductive stabilization effect • Initial substitution do not result in significantly increased stabilization. • Relative oxidative stability of common anions agrees with recent work by Ue et al. • PF6 > BF4 > TFSI

  14. Func. Group Substitutions on 1,2,3-trimethylimidazolium EW by Res. EW by Ind. EW by Ind. ED by Res. ED by Ind. EW by Ind. ED by Res.

  15. Position of Substitution ED Resonance Effect Dominates Over EW Inductive Effect EW Inductive Effect Dominates Over ED Resonance Effect

  16. Func. Group Substitutions on PF5CF3 anion

  17. Conclusions • Trends in EAs of cations and IEs of Anions are generally consistent with relative experimental redox stability • Efficient computational methods can be used to quickly screen candidate IL structures to maximize electrochemical windows • Effect on redox stability due to combination of inductive and resonance effects, relative strength of which depends on substitution position

  18. Acknowledgements • Advisor: Prof. GerbrandCeder • Collaborators • Prof. Nicola Marzari • OlivieroAndreussi • Sponsors : under the Dupont-MIT Alliance

  19. Thank you

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