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Title: Crowding and Anomalous Capacitance at an Electrode-Ionic Liquid Interface Observed Using Operando X-ray Scattering

Room temperature ionic liquids are widely recognized as novel electrolytes with properties very different from those of aqueous solutions, and thus with many potential applications, but observing how they actually behave at electrolytic interfaces has proved to be challenging. We have studied the voltage-dependent structure of [TDTHP]+[NTF2]- near its interface with an electrode, using in situ synchrotron X-ray reflectivity. An anion-rich layer develops at the interface above a threshold voltage of +1.75 V, and the layer thickness increases rapidly with voltage, reaching ~6 nm (much larger that the anion dimensions) at +2.64 V. Our results provide direct confirmation of the theoretical prediction of “crowding” of ions near the interface. The interfacial layer is not purely anionic but a mixture of up to ~80% anions and the rest cations. Moreover, the static differential capacitance calculated from X-ray measurements shows an increase at higher voltages, consistent with a recent zero-frequency capacitance measurement but inconsistent with ac capacitance measurements.
Authors:
 [1] ;  [1] ;  [1]
  1. Northwestern Univ., Evanston, IL (United States)
Publication Date:
OSTI Identifier:
1243121
Resource Type:
Journal Article
Resource Relation:
Journal Name: ACS Central Science; Journal Volume: 2; Journal Issue: (3) ; 03, 2016
Research Org:
Advanced Photon Source (APS), Argonne National Laboratory (ANL), Argonne, IL (US)
Sponsoring Org:
National Science Foundation, Arlington, VA (United States)
Country of Publication:
United States
Language:
ENGLISH
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS