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Title: Interfacial ionic ‘liquids’: connecting static and dynamic structures

It is well known that room temperature ionic liquids (RTILs) often adopt a charge-separated layered structure, i.e. with alternating cation- and anion-rich layers, at electrified interfaces. However, the dynamic response of the layered structure to temporal variations in applied potential is not well understood. In this study, we used in situ, real-time x-ray reflectivity to study the potential-dependent electric double layer (EDL) structure of an imidazolium-based RTIL on charged epitaxial graphene during potential cycling as a function of temperature. The results suggest that the graphene–RTIL interfacial structure is bistable in which the EDL structure at any intermediate potential can be described by the combination of two extreme-potential structures whose proportions vary depending on the polarity and magnitude of the applied potential. This picture is supported by the EDL structures obtained by fully atomistic molecular dynamics simulations at various static potentials. The potential-driven transition between the two structures is characterized by an increasing width but with an approximately fixed hysteresis magnitude as a function of temperature. Finally, the results are consistent with the coexistence of distinct anion- and cation-adsorbed structures separated by an energy barrier (~0.15 eV).
Authors:
 [1] ;  [2] ;  [3] ;  [1] ;  [3] ;  [3] ;  [4] ;  [4] ;  [5] ;  [5] ;  [1]
  1. Argonne National Lab. (ANL), Argonne, IL (United States). Chemical Science and Engineering Division
  2. Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source
  3. Vanderbilt Univ., Nashville, TN (United States). Dept. of Chemical and Biomolecular Engineering
  4. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Chemical Sciences Division
  5. Drexel Univ., Philadelphia, PA (United States). Dept. of Materials Science and Engineering. AJ Drexel Nanomaterials Inst.
Publication Date:
OSTI Identifier:
1302908
Grant/Contract Number:
AC02-06CH11357; AC02-05CH11231
Type:
Accepted Manuscript
Journal Name:
Journal of Physics. Condensed Matter
Additional Journal Information:
Journal Volume: 27; Journal Issue: 3; Journal ID: ISSN 0953-8984
Publisher:
IOP Publishing
Research Org:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Contributing Orgs:
Vanderbilt Univ., Nashville, TN (United States); Drexel Univ., Philadelphia, PA (United States)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY ionic liquid; supercapacitor; electric double layer; epitaxial graphene; x-ray reflectivity; RTIL; interfacial structure