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This content will become publicly available on September 21, 2018

Title: Effects of electrolytes on redox potentials through ion pairing

Here, reduction potentials have been determined for two molecules, benzophenone (BzPh) and perylene (Per), effectively in the complete absence of electrolyte as well as in the presence of three different supporting electrolytes in the moderately polar solvent THF. A description of how this can be so, and qualifications, are described in the discussion section. The primary tool in this work, pulse radiolysis, measures electron transfer (ET) equilibria in solution to obtain differences in redox potentials. Voltammetry measures redox potentials by establishing ET equilibria at electrodes, but electrolytes are needed for current flow. Results here show that without electrolyte the redox potentials were 100–451 mV more negative than those with 100 mM electrolyte. These changes depended both on the molecule and the electrolyte. In THF the dominant contributor to stabilization of radical anions by electrolyte was ion pairing. An equation was derived to give changes in redox potentials when electrolyte is added in terms of ion pair dissociation constants and activity coefficients. Definite values were determined for energetics, ΔG d°, of ion pairing. Values of ΔG d° for pairs with TBA + give some doubt that it is a “weakly-coordinating cation.” Computations with DFT methods were moderately successful at describing themore » ion paring energies.« less
Authors:
 [1] ;  [2] ;  [1] ;  [1] ;  [1] ; ORCiD logo [1]
  1. Brookhaven National Lab. (BNL), Upton, NY (United States)
  2. Doshisha Univ., Nara (Japan)
Publication Date:
Report Number(s):
BNL-114474-2017-JA
Journal ID: ISSN 1572-6657; R&D Project: CO037; KC0304030
Grant/Contract Number:
SC0012704
Type:
Accepted Manuscript
Journal Name:
Journal of Electroanalytical Chemistry
Additional Journal Information:
Journal Volume: 804; Journal Issue: C; Journal ID: ISSN 1572-6657
Publisher:
Elsevier
Research Org:
Brookhaven National Laboratory (BNL), Upton, NY (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Redox potentials; Ion pair; Electrolyte; Voltammetry
OSTI Identifier:
1405940