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Experimental measurement and prediction of ionic liquid ionisation energies

DOI: 10.1039/D1CP02441H DOI Help

Authors: Jake Seymour (University of Reading) , Ekaterina Gousseva (University of Reading) , Alex Large (University of Reading) , Coby J. Clarke (University of Nottingham) , Peter Licence (University of Nottingham) , Richard M. Fogarty (Imperial College London) , David A. Duncan (Diamond Light Source) , Pilar Ferrer (Diamond Light Source) , Federica Venturini (Diamond Light Source) , Roger A. Bennett (University of Reading) , Robert G. Palgrave (University College London) , Kevin R. J. Lovelock (University of Reading)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Physical Chemistry Chemical Physics

State: Published (Approved)
Published: September 2021
Diamond Proposal Number(s): 20463 , 24304 , 25929

Open Access Open Access

Abstract: Ionic liquid (IL) valence electronic structure provides key descriptors for understanding and predicting IL properties. The ionisation energies of 60 ILs are measured and the most readily ionised valence state of each IL (the highest occupied molecular orbital, HOMO) is identified using a combination of X-ray photoelectron spectroscopy (XPS) and synchrotron resonant XPS. A structurally diverse range of cations and anions were studied. The cation gave rise to the HOMO for nine of the 60 ILs presented here, meaning it is energetically more favourable to remove an electron from the cation than the anion. The influence of the cation on the anion electronic structure (and vice versa) were established; the electrostatic effects are well understood and demonstrated to be consistently predictable. We used this knowledge to make predictions of both ionisation energy and HOMO identity for a further 516 ILs, providing a very valuable dataset for benchmarking electronic structure calculations and enabling the development of models linking experimental valence electronic structure descriptors to other IL properties, e.g. electrochemical stability. Furthermore, we provide design rules for the prediction of the electronic structure of ILs.

Subject Areas: Chemistry

Instruments: B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS , I09-Surface and Interface Structural Analysis

Added On: 18/09/2021 10:04


Discipline Tags:

Physical Chemistry Chemistry

Technical Tags:

Spectroscopy X-ray Photoelectron Spectroscopy (XPS)