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Title: In situ XANES and EXAFS Analysis of Redox Active Fe Center Ionic Liquids

We apply in situ X-Ray Absorption Near Edge Spectroscopy (XANES) and Extended X-Ray Absorption Fine Structure (EXAFS) techniques to a metal center ionic liquid undergoing oxidation and reduction in a three electrode spectroscopic cell. Furthermore, the determination of the extent of reduction under negative bias on the working electrode and the extent of oxidation are determined after pulse voltammetry to quiescence. While the ionic liquid undergoes full oxidation, it undergoes only partial reduction, likely due to transport issues on the timescale of the experiment. Nearest neighbor Fe-O distances in the fully oxidized state match well to expected values for similarly coordinated solids, but reduction does not result in an extension of the Fe-O bond length, as would be expected from comparisons to the solid phase. Instead, little change in bond length is observed. Finally, we suggest that this may be due to a more complex interaction between the monodentate ligands of the metal center anion and the surrounding charge cloud, rather than straightforward electrostatics between the metal center and the nearest neighbor grouping.
Authors:
ORCiD logo [1] ;  [2] ;  [2] ;  [2] ;  [3] ;  [3] ;  [2]
  1. Joint Center for Energy Storage Reseach, Albuquerque, NM (United States); Sandia National Lab. (SNL-NM), Albuquerque, NM (United States). Power Sources Technology Group
  2. Univ. of Maine, Orono, ME (United States). Dept. of Physics and Astronomy
  3. Sandia National Lab. (SNL-NM), Albuquerque, NM (United States). Power Sources Technology Group
Publication Date:
Report Number(s):
SAND2016-12355J
Journal ID: ISSN 0013-4686; 649726
Grant/Contract Number:
AC04-94AL85000; AC02-98CH10886
Type:
Accepted Manuscript
Journal Name:
Electrochimica Acta
Additional Journal Information:
Journal Volume: 185; Journal Issue: C; Journal ID: ISSN 0013-4686
Publisher:
Elsevier
Research Org:
Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); USDOE Office of Electricity Delivery and Energy Reliability (OE)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; 25 ENERGY STORAGE; Electrochemistry; in situ XANES; in situ EXAFS; Redox active Ionic Liquids; Flow Batteries
OSTI Identifier:
1338380
Alternate Identifier(s):
OSTI ID: 1359034