title: A Neutron Diffraction Study of the Electrochemical Double Layer Capacitor Electrolyte Tetrapropylammonium Bromide in Acetonitrile.
abstract: Neutron diffraction with isotopic substitution has been used to characterize the bulk liquid structure of the technologically relevant electrolyte solution, 1 M tetrapropylammonium bromide (TPA Br) in acetonitrile (acn), and of pure deuterated acetonitrile. Empirical potential structure refinement modeling procedures have been used to extract detailed structural information about solvent-solvent, solvent-ion, and ion-ion correlations. Analysis of the refined data shows the expected local dipolar conformation of acn in the pure solvent. This short-range dipolar ordering is also present within the solutions of TPA Br in acn, and it affects how the solvent orders itself around the ions. The solvation numbers of the TPA cations and the bromide anions are deduced, 8 and 5, respectively, as are the orientations of the solvent molecules that surround the ions. Evidence for ion association is also presented, with nearly two-thirds of the ions in the system being in associated pairs or clusters.
authors.affiliation: Department of Chemistry, University of Cambridge , Lensfield Road, Cambridge CB2 1EW, United Kingdom.
authors.forename: Elizabeth K
authors.initials: EK
authors.lastname: Humphreys
authors.affiliation: Department of Chemistry, University of Cambridge , Lensfield Road, Cambridge CB2 1EW, United Kingdom.|Gonville and Caius College , Trinity Street, Cambridge CB2 1TA, United Kingdom.
authors.forename: Phoebe K
authors.initials: PK
authors.lastname: Allan
authors.affiliation: Department of Chemistry, University of Cambridge , Lensfield Road, Cambridge CB2 1EW, United Kingdom.|BP Institute, University of Cambridge , Madingley Road, Cambridge CB3 0EZ, United Kingdom.
authors.forename: Rebecca J L
authors.initials: RJ
authors.lastname: Welbourn
authors.affiliation: ISIS Facility, STFC Rutherford Appleton Laboratory , Harwell Oxford, Didcot, OX11 0QX, United Kingdom.
authors.forename: Tristan G A
authors.initials: TG
authors.lastname: Youngs
authors.affiliation: ISIS Facility, STFC Rutherford Appleton Laboratory , Harwell Oxford, Didcot, OX11 0QX, United Kingdom.
authors.forename: Alan K
authors.initials: AK
authors.lastname: Soper
authors.affiliation: Department of Chemistry, University of Cambridge , Lensfield Road, Cambridge CB2 1EW, United Kingdom.
authors.forename: Clare P
authors.initials: CP
authors.lastname: Grey
authors.affiliation: Department of Chemistry, University of Cambridge , Lensfield Road, Cambridge CB2 1EW, United Kingdom.|BP Institute, University of Cambridge , Madingley Road, Cambridge CB3 0EZ, United Kingdom.
authors.forename: Stuart M
authors.initials: SM
authors.lastname: Clarke