skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Effects of electrolytes on redox potentials through ion pairing

Abstract

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:
Research Org.:
Brookhaven National Laboratory (BNL), Upton, NY (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1405940
Report Number(s):
BNL-114474-2017-JA
Journal ID: ISSN 1572-6657; R&D Project: CO037; KC0304030
Grant/Contract Number:
SC0012704
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Journal of Electroanalytical Chemistry
Additional Journal Information:
Journal Volume: 804; Journal Issue: C; Journal ID: ISSN 1572-6657
Publisher:
Elsevier
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Redox potentials; Ion pair; Electrolyte; Voltammetry

Citation Formats

Bird, Matthew J., Iyoda, Tomokazu, Bonura, Nicholas, Bakalis, Jin, Ledbetter, Abram J., and Miller, John R. Effects of electrolytes on redox potentials through ion pairing. United States: N. p., 2017. Web. doi:10.1016/j.jelechem.2017.09.030.
Bird, Matthew J., Iyoda, Tomokazu, Bonura, Nicholas, Bakalis, Jin, Ledbetter, Abram J., & Miller, John R. Effects of electrolytes on redox potentials through ion pairing. United States. doi:10.1016/j.jelechem.2017.09.030.
Bird, Matthew J., Iyoda, Tomokazu, Bonura, Nicholas, Bakalis, Jin, Ledbetter, Abram J., and Miller, John R. 2017. "Effects of electrolytes on redox potentials through ion pairing". United States. doi:10.1016/j.jelechem.2017.09.030.
@article{osti_1405940,
title = {Effects of electrolytes on redox potentials through ion pairing},
author = {Bird, Matthew J. and Iyoda, Tomokazu and Bonura, Nicholas and Bakalis, Jin and Ledbetter, Abram J. and Miller, John R.},
abstractNote = {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, ΔGd°, of ion pairing. Values of ΔGd° for pairs with TBA+ give some doubt that it is a “weakly-coordinating cation.” Computations with DFT methods were moderately successful at describing the ion paring energies.},
doi = {10.1016/j.jelechem.2017.09.030},
journal = {Journal of Electroanalytical Chemistry},
number = C,
volume = 804,
place = {United States},
year = 2017,
month = 9
}

Journal Article:
Free Publicly Available Full Text
This content will become publicly available on September 21, 2018
Publisher's Version of Record

Save / Share:
  • Redox flow battery (RFB) is a promising candidate for energy storage component in designing resilient grid scale power supply due to the advantage of the separation of power and energy. However, poorly understood chemical and thermal stability issues of electrolytes currently limit the performance of RFB. Designing of high performance stable electrolytes requires comprehensive knowledge about the molecular level solvation structure and dynamics of their redox active species. The molecular level understanding of detrimental V2O5 precipitation process led to successful designing of mixed acid based electrolytes for vanadium redox flow batteries (VRFB). The higher stability of mixed acid based electrolytesmore » is attributed to the choice of hydrochloric acid as optimal co-solvent, which provides chloride anions for ligand exchange process in vanadium solvation structure. The role of chloride counter anion on solvation structure and dynamics of vanadium species were studied using combined magnetic resonance spectroscopy and DFT based theoretical methods. Finally, the solvation phenomenon of multiple vanadium species and their impact on VRFB electrolyte chemical stability were discussed.« less
  • Precise measurements of viscosity and conductivity have been made of the solutions of sodium triflate and lithium perchlorate in poly(propylene oxide) of MW 4000 (PPG(4000)) studied spectroscopically by Torella and co-workers for the extent of ion association. Viscosity, but not conductivity, data conform very well to the VTF equation and yield ideal glass transition temperatures the track the measured glass transition temperatures as closely as in the case of glass-forming aqueous solutions. The differences in temperature dependences of the two processes are demonstrated by using Walden rule plots. Using the data of Torell et al. at ambient temperature as amore » calibration point, the authors show that the deviations of conductivity from viscosity-dictated behavior predict almost quantitatively the strong temperature dependence of the free ion concentration found by Torell et al. up to the high temperature limit of their measurements.« less
  • The stability of the electrolytes for all-vanadium redox flow battery was investigated with ex-situ heating/cooling treatment and in-situ flow-battery testing methods. The effects of inorganic and organic additives have been studied. The additives containing the ions of potassium, phosphate, and polyphosphate are not suitable stabilizing agents because of their reactions with V(V) ions, forming precipitates of KVSO6 or VOPO4. Of the chemicals studied, polyacrylic acid and its mixture with CH3SO3H are the most promising stabilizing candidates which can stabilize all the four vanadium ions (V2+, V3+, VO2+, and VO2+) in electrolyte solutions up to 1.8 M. However, further effort ismore » needed to obtain a stable electrolyte solution with >1.8 M V5+ at temperatures higher than 40 °C.« less
  • A recently-developed instrument for time-resolved infrared detection following pulse radiolysis has been used to measure the ν(C≡N) IR band of the radical anion of a CN-substituted fluorene in tetrahydrofuran. Specific vibrational frequencies can exhibit distinct frequency shifts due to ion-pairing, which can be explained in the framework of the vibrational Stark effect. Measurements of the ratio of free ions and ion-pairs in different electrolyte concentrations allowed us to obtain an association constant and free energy change for ion-pairing. As a result, this new method has the potential to probe the geometry of ion-pairing and allows the reduction potentials of moleculesmore » to be determined in the absence of electrolyte in an environment of low dielectric constant.« less