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

Title: Experimental Insight into the Thermodynamics of the Dissolution of Electrolytes in Room-Temperature Ionic Liquids: From the Mass Action Law to the Absolute Standard Chemical Potential of a Proton

Journal Article · · ACS Omega
 [1]; ORCiD logo [2];  [1]
  1. Department of Material and Life Chemistry, Kanagawa University, 3-27-1 Rokkakubashi, Kanagawa-ku, Yokohama 221-8686, Japan
  2. Chemistry Division, Brookhaven National Laboratory, P.O. Box 5000, Upton, New York 11973-5000, United States

Room-temperature ionic liquids (ILs) are a class of nonaqueous solvents that have expanded the realm of modern chemistry, drawing increasing interest over the last few decades, not only in terms of their own unique physical chemistry but also in many applications including organic synthesis, electrochemistry, and biological systems, wherein charged solutes (i.e., electrolytes) often play vital roles. But, our fundamental understanding of the dissolution of an electrolyte in an IL is still rather limited. For example, the activity of a charged species has frequently been assumed to be unity without a clear experimental basis. In this study, we have discussed a standard component-based scheme for the dissolution of an electrolyte in an IL, supported by our observation of ideal Nernstian responses for the reduction of silver and ferrocenium salts in a representative IL, 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([emim+][NTf2-] or [emim+][TFSI-]). Using this scheme, which was also supported by temperature-dependent measurements with ILs having longer alkyl chains in the imidazolium ring, and the solubility of the IL in water, we established the concept of Gibbs transfer energies of “pseudo-single ions” from the IL to conventional neutral molecular solvents (water, acetonitrile, and methanol). This concept, which bridges component- and constituent-based energetics, utilizes an extrathermodynamic assumption, which itself was justified by experimental observations. Furthermore, these energies enable us to eliminate inner potential differences between the IL and molecular solvents (solvent-solvent interactions), that is, on a practical level, conditional liquid junction potential differences, so that we can discuss ion-solvent interactions independently. Specifically, we have examined the standard electrode potential of the ferrocenium/ferrocene redox couple, Fc+/Fc, and the absolute intrinsic standard chemical potential of a proton in [emim+][NTf2-], finding that the proton is more acidic in the IL than in water by 6.5 ± 0.6 units on the unified pH scale. Finally, our results strengthen the progress on the physical chemistry of ions in IL solvent systems on the basis of their activities, providing a rigorous thermodynamic framework.

Research Organization:
Brookhaven National Laboratory (BNL), Upton, NY (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Basic Energy Sciences (BES)
Grant/Contract Number:
SC0012704; SC00112704
OSTI ID:
1337583
Alternate ID(s):
OSTI ID: 1339945; OSTI ID: 1341613
Report Number(s):
BNL-113339-2016-JA
Journal Information:
ACS Omega, Journal Name: ACS Omega Vol. 1 Journal Issue: 6; ISSN 2470-1343
Publisher:
American Chemical SocietyCopyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 14 works
Citation information provided by
Web of Science

References (167)

Ionic liquids: perspectives for organic and catalytic reactions journal May 2002
Single-Ion Solvation Free Energies and the Normal Hydrogen Electrode Potential in Methanol, Acetonitrile, and Dimethyl Sulfoxide journal January 2007
A Facile High-Yield Synthesis and Purification of Tetrabutylammonium Tetrabutylborate journal January 1998
Toward Understanding the Origin of Positive Effects of Ionic Liquids on Catalysis: Formation of More Reactive Catalysts and Stabilization of Reactive Intermediates and Transition States in Ionic Liquids journal July 2010
Thermodynamic and Kinetic Hydricity of Ruthenium(II) Hydride Complexes journal September 2012
Fundamental Experimental Problems book January 2011
Ionic Liquids:  First Direct Determination of their Cohesive Energy
  • Santos, Luís M. N. B. F.; Canongia Lopes, José N.; Coutinho, João A. P.
  • Journal of the American Chemical Society, Vol. 129, Issue 2 https://doi.org/10.1021/ja067427b
journal January 2007
Electrophilic Addition and Substitution Reactions of Bis((trifluoromethyl)sulfonyl)amide and Its N-Chloro Derivative journal July 1994
Standard p K a Scales of Carbon-Centered Indicator Acids in Ionic Liquids: Effect of Media and Structural Implication journal August 2012
Determining the Gibbs Energy of Ion Transfer Across Water-Organic Liquid Interfaces with Three-Phase Electrodes journal January 2005
Critical study involving water, methanol, acetonitrile, N,N-dimethylformamide, and dimethyl sulfoxide of medium ion activity coefficients, .gamma., on the basis of the .gamma.AsPh4+ = .gamma.BPh4- assumption journal July 1972
Gibbs Energies of Transfer of Anions from Water to Mixed Aqueous Organic Solvents journal August 2007
Toward Prediction of the Chemistry in Ionic Liquids: An Accurate Computation of Absolute p K a Values of Benzoic Acids and Benzenethiols journal August 2015
Subnanoscale hydrophobic modulation of salt bridges in aqueous media journal April 2015
Quantum design of ionic liquids for extreme chemical inertness and a new theory of the glass transition journal January 2013
Biocatalysis in Ionic Liquids journal June 2007
Molecular Solutes in Ionic Liquids: A Structural Perspective journal November 2007
The hydrogen evolution reaction in a room temperature ionic liquid: mechanism and electrocatalyst trends journal January 2012
Solid–Liquid Equilibria Measurements of Mixtures of Lithium Bis(trifluoromethanesulfonyl)imide with Varying Alkyl Chain Length Ammonium Bis(trifluoromethanesulfonyl)imide Ionic Liquids journal January 2016
Excess Magnitudes for Ionic Liquid Binary Mixtures with a Common Ion journal June 2007
Standard Electrode Potentials and Temperature Coefficients in Water at 298.15 K journal January 1989
Toward a p K a Scale of N-base Amines in Ionic Liquids journal April 2014
Metallocenium Ionic Liquids journal June 2010
The formal potentials and electrode kinetics of the proton/hydrogen couple in various room temperature ionic liquids journal January 2012
Ionic liquids behave as dilute electrolyte solutions journal May 2013
Selective Oxidation and Reduction of Trinuclear Titanium(II) Hexaazatrinaphthylene ComplexesSynthesis, Structure, and Electrochemical Investigations journal July 2007
Direct Determination of Equilibrium Potentials for Hydrogen Oxidation/Production by Open Circuit Potential Measurements in Acetonitrile journal June 2012
Electrochemical Proton Reduction and Equilibrium Acidity (p K a ) in Aprotic Ionic Liquids: Phenols, Carboxylic Acids, and Sulfonic Acids journal September 2015
Electrochemical Proton Reduction and Equilibrium Acidity (p K a ) in Aprotic Ionic Liquids: Protonated Amines and Sulfonamide Acids journal September 2015
Scope and limitations of imidazolium-based ionic liquids as room temperature glycosylation promoters journal January 2010
Phase-boundary potential across the nonpolarized interface between the room-temperature molten salt and water journal February 2003
Concepts and Definitions book January 2011
Solvation of ions. XVI. Solvent activity coefficients of single ions. Recommended extrathermodynamic assumption journal February 1972
Reply to Perkin et al.: Experimental observations demonstrate that ionic liquids form both bound (Stern) and diffuse electric double layers journal October 2013
Amperometric Ion-Selective Electrode for Alkali Metal Cations Based on a Room-Temperature Ionic Liquid Membrane journal September 2009
Is Amine a Stronger Base in Ionic Liquid Than in Common Molecular Solvent? An Accurate Basicity Scale of Amines journal August 2015
Why Are Ionic Liquids Liquid? A Simple Explanation Based on Lattice and Solvation Energies journal October 2006
Charged ligands for catalyst immobilisation and analysis journal January 2008
Electrode Potentials in Acetonitrile. Estimation of the Liquid Junction Potential between Acetonitrile Solutions and the Aqueous Saturated Calomel Electrode 1 journal September 1965
Solvation of ions. XIV. Protic-dipolar aprotic solvent effects on rates of bimolecular reactions. Solvent activity coefficients of reactants and transition states at 25°. journal September 1968
Thermodynamic Aspects of Electrocatalytic CO 2 Reduction in Acetonitrile and with an Ionic Liquid as Solvent or Electrolyte journal October 2015
Electrochemistry in Room Temperature Ionic Liquids: A Review and Some Possible Applications journal October 2006
The Ionic Basis of Electrical Activity in Nerve and Muscle journal November 1951
Unified pH Values of Liquid Chromatography Mobile Phases journal February 2015
Mixing ionic liquids – “simple mixtures” or “double salts”? journal January 2014
Single ion free energies of some ions and the hydrophobic interactions of Ph4AsBPh4 and Ph4SbBPh4 in mixed ethanol-water solvents journal December 1989
First Examples of α-(1→4)-Glycosylation Reactions on Ionic Liquid Supports journal October 2010
The synthesis and thermolysis of imidazole quaternary salts journal January 1977
Ionic Liquid-Mediated Selective Conversion of CO2 to CO at Low Overpotentials journal September 2011
Influence of the Cation on the Solubility of CO2 and H2 in Ionic Liquids Based on the Bis(trifluoromethylsulfonyl)imide Anion journal June 2007
Room-Temperature Ionic Liquids. Solvents for Synthesis and Catalysis journal August 1999
Studies on the liquid junction potential corrections of electrolytes at aqueous + mixed solvent boundaries journal November 1987
Medium effects for single ions in acetonitrile and ethanol-water solvents based on reference-electrolyte assumption journal April 1972
Ionic liquids form ideal solutions journal January 2011
Dielectric constant of water from 0 to 100 C journal January 1956
Approach for Predicting the Standard Free Energy Solvation of H + and Acidity Constant in Nonaqueous Organic Solvents journal August 2014
Nanoscale Segregation in Room Temperature Ionic Liquids journal May 2007
Mixing Enthalpy for Binary Mixtures Containing Ionic Liquids journal May 2016
Solubilities and medium effects of tetraphenylgermane, tetraphenylmethane, and tetraphenylsilane in acetonitrile, methanol, and some ethanol-water solvents journal April 1972
Ionic liquids based on (fluorosulfonyl)(pentafluoroethanesulfonyl)imide with various oniums journal September 2010
Voltammetry in Room Temperature Ionic Liquids: Comparisons and Contrasts with Conventional Electrochemical Solvents. journal February 2010
Resonance Raman spectroscopy of the lowest excited state of derivatives of tris(2,2'-bipyridine)ruthenium(II): substituent effects on electron localization in mixed-ligand complexes journal February 1986
Electronic and Steric Effects: How Do They Work in Ionic Liquids? The Case of Benzoic Acid Dissociation journal June 2010
Modern Electrochemistry 1 book January 1998
A Unified pH Scale for All Phases journal August 2010
Protic Ionic Liquids:  Properties and Applications journal January 2008
Solubility products of tetraphenylarsonium and tetraphenylphosphonium picrates in ethanol-water solvents at 25.deg. journal April 1972
Metal Triflimidates: Better than Metal Triflates as Catalysts in Organic Synthesis-The Effect of a Highly Delocalized Counteranion journal August 2010
A New Salt Bridge Based on the Hydrophobic Room-Temperature Molten Salt journal July 2006
Thermodynamics of cellulose dissolution in an imidazolium acetate ionic liquid journal January 2015
Are Room-Temperature Ionic Liquids Dilute Electrolytes? journal December 2014
Mass Transport Studies and Hydrogen Evolution at a Platinum Electrode Using Bis(trifluoromethanesulfonyl)imide as the Proton Source in Ionic Liquids and Conventional Solvents journal December 2014
Electrochemical Determination of p K a of N-Bases in Ionic Liquid Media journal December 2011
Cyclic voltammetry of ion transfer across a room temperature ionic liquid membrane supported by a microporous filter journal October 2007
Response of PVC membrane ion-selective electrodes to alkylmethylimidazolium ionic liquid cations journal September 2013
Dilute or Concentrated Electrolyte Solutions? Insight from Ionic Liquid/Water Electrolytes journal August 2015
Solvation Structure and Transport of Acidic Protons in Ionic Liquids:  A First-principles Simulation Study journal May 2006
Catalysts with ionic tag and their use in ionic liquids journal January 2008
Mutual Solubilities of Water and the [C n mim][Tf 2 N] Hydrophobic Ionic Liquids journal February 2008
Comparison of the Conductivity Properties of the Tetrabutylammonium Salt of Tetrakis(pentafluorophenyl)borate Anion with Those of Traditional Supporting Electrolyte Anions in Nonaqueous Solvents journal November 2004
Room-Temperature Ionic Liquids: Solvents for Synthesis and Catalysis. 2 journal May 2011
Measuring and predicting ΔvapH298 values of ionic liquids journal January 2009
Understanding Ionic Liquids at the Molecular Level: Facts, Problems, and Controversies journal January 2008
Ionic Liquid (Molten Salt) Phase Organometallic Catalysis journal October 2002
Oligomannan Synthesis Using Ionic Liquid Supported Glycosylation journal December 2007
The absolute electrode potential: an explanatory note (Recommendations 1986) journal January 1986
Lanthanides and Actinides in Ionic Liquids journal June 2007
Absolute Potential of the Standard Hydrogen Electrode and the Problem of Interconversion of Potentials in Different Solvents journal June 2010
Weakly Polar Aprotic Ionic Liquids Acting as Strong Dissociating Solvent: A Typical “Ionic Liquid Effect” Revealed by Accurate Measurement of Absolute p K a of Ylide Precursor Salts journal April 2016
Is a Stern and diffuse layer model appropriate to ionic liquids at surfaces? journal October 2013
A pH Scale for the Protic Ionic Liquid Ethylammonium Nitrate journal April 2016
Ionic Liquids at Electrified Interfaces journal March 2014
Solubilities of Potassium, Triisoamylbutylammonium, and Tetrabutylammonium Tetraphenylborides and Picrates in Water and Methanol and Their Medium Effects at 25° journal May 1966
Long-range electrostatic screening in ionic liquids journal May 2015
The Protoelectric Potential Map (PPM): An Absolute Two-Dimensional Chemical Potential Scale for a Global Understanding of Chemistry journal March 2014
Isothermogravimetric Determination of the Enthalpies of Vaporization of 1-Alkyl-3-methylimidazolium Ionic Liquids journal July 2008
Dielectric Constants of the Methanol-Water System from 5 to 55° 1 journal June 1946
Electrochemical Reactivity in Room-Temperature Ionic Liquids journal July 2008
Mixtures of ionic liquids journal January 2012
Electrocatalytic CO 2 Reduction with a Homogeneous Catalyst in Ionic Liquid: High Catalytic Activity at Low Overpotential journal May 2014
Gas Solubility in Ionic Liquids journal November 2013
Static Dielectric Constants of Acetonitrile/Water Mixtures at Different Temperatures and Debye−Hückel A and a 0 B Parameters for Activity Coefficients journal May 2007
Modern Room Temperature Ionic Liquids, a Simple Guide to Understanding Their Structure and How It May Relate to Dynamics journal August 2015
Potentiometry in Nonaqueous Solutions book September 2009
Densities and Viscosities of the Binary Mixtures of 1-Ethyl-3-methylimidazolium Bis(trifluoromethylsulfonyl)imide with N -Methyl-2-pyrrolidone or Ethanol at T = (293.15 to 323.15) K journal February 2012
Self-diffusion of a molecule in porous Vycor glass journal January 1986
Voltammetric Studies of Gold, Protons, and [HCl 2 ] - in Ionic Liquids journal June 2007
Standard and Absolute p K a Scales of Substituted Benzoic Acids in Room Temperature Ionic Liquids journal December 2013
Measurement of real free energies of transfer of individual ions from water to other solvents with the jet cell journal October 1991
The measurement of the diffusion coefficients of ferrocene and ferrocenium and their temperature dependence in acetonitrile using double potential step microdisk electrode chronoamperometry journal September 2010
Meaning and Measurability of Single-Ion Activities, the Thermodynamic Foundations of pH, and the Gibbs Free Energy for the Transfer of Ions between Dissimilar Materials journal April 2015
Ionic Liquids of Cationic Sandwich Complexes journal April 2012
Ionic Liquids: The Link to High-Temperature Molten Salts? journal May 2007
Transfer activity coefficients of ions in methanol-water solvents based on the tetraphenylborate assumption journal August 1984
Ferrocene as a Reference Redox Couple for Aprotic Ionic Liquids journal October 2009
Nanostructural Organization in Ionic Liquids journal February 2006
Going Full Circle: Phase‐Transition Thermodynamics of Ionic Liquids journal April 2011
A Versatile Ruthenium Precursor for Biphasic Catalysis and Its Application in Ionic Liquid Biphasic Transfer Hydrogenation:  Conventional vs Task-Specific Catalysts journal June 2004
Vapourisation of ionic liquids journal January 2007
Development of Molecular Electrocatalysts for Energy Storage journal February 2014
Salts dissolved in salts: ionic liquid mixtures journal January 2011
Ionophilic Phosphines:  Versatile Ligands for Ionic Liquid Biphasic Catalysis journal December 2007
Simple Ion Transfer at Liquid|Liquid Interfaces journal January 2012
Ionic Liquids: Science and Applications book January 2012
How ideal are binary mixtures of room-temperature ionic liquids? journal April 2010
Ionic Liquids: New Targets and Media for α-Amino Acid and Peptide Chemistry journal December 2008
Controlling Hydrolysis Reaction Rates with Binary Ionic Liquid Mixtures by Tuning Hydrogen-Bonding Interactions journal February 2012
Ionic Liquids in Heterocyclic Synthesis journal June 2008
Relative molar Gibbs energies of cation transfer from a molecular liquid to ionic liquids at 298.15 K journal January 2003
Copper(I) and Silver(I) Bis(trifluoromethanesulfonyl)imide and Their Interaction with an Arene, Diverse Olefins, and an NTf 2 -Based Ionic Liquid journal November 2012
Effect of Water on the Electrochemical Window and Potential Limits of Room-Temperature Ionic Liquids journal December 2008
Correlation between the standard Gibbs energies of an anion transfer from water to highly hydrophobic ionic liquids and to 1,2-dichloroethane journal February 2014
Pure H- conduction in oxyhydrides journal March 2016
Structure and Solvation in Ionic Liquids journal November 2007
Predictive Molecular Thermodynamic Models for Liquid Solvents, Solid Salts, Polymers, and Ionic Liquids journal March 2008
Solution Thermodynamics of Imidazolium-Based Ionic Liquids and Water journal November 2001
Volumetric Properties of Binary Mixtures Containing Ionic Liquids and Some Aprotic Solvents journal September 2010
Energy applications of ionic liquids journal January 2009
The Acidity of the HBr/AlBr 3 System: Stabilization of Crystalline Protonated Arenes and Their Acidity in Bromoaluminate Ionic Liquids journal March 2015
Solubility product of silver tetraphenylborate in water and methanol journal January 1972
Catalysis in Ionic Liquids journal June 2007
Tetraoctylphosphonium Tetrakis(pentafluorophenyl)borate Room Temperature Ionic Liquid toward Enhanced Physicochemical Properties for Electrochemistry journal October 2012
Ionic Liquids and Their Interaction with Cellulose journal December 2009
Single-ion gibbs energies, enthalpies and entropies of transfer from water to aqueous methanol based on the (Ph4P+, Ph4As+)= Ph4B– assumption
  • Abraham, Michael H.; Hill, Tony; Ling, How Chiong
  • Journal of the Chemical Society, Faraday Transactions 1: Physical Chemistry in Condensed Phases, Vol. 80, Issue 2 https://doi.org/10.1039/f19848000489
journal January 1984
Anchor Points for the Unified Brønsted Acidity Scale: The rCCC Model for the Calculation of Standard Gibbs Energies of Proton Solvation in Eleven Representative Liquid Media journal May 2011
Charge-transfer processes at the interface between hydrophobic ionic liquid and water journal July 2009
Gibbs Energies of Transfer of Cations from Water to Mixed Aqueous Organic Solvents journal March 2000
Evaluation of a Ag∣Ag+ reference electrode for use in room temperature ionic liquids journal September 2006
An oxyhydride of BaTiO3 exhibiting hydride exchange and electronic conductivity journal April 2012
A Cryptate Reference Electrode for Ionic Liquids journal September 2008
Experimental Vapor Pressures of 1-Alkyl-3-methylimidazolium Bis(trifluoromethylsulfonyl)imides and a Correlation Scheme for Estimation of Vaporization Enthalpies of Ionic Liquids journal June 2006
Ionic liquids as electrolytes journal August 2006
Aqueous Solvation Free Energies of Ions and Ion−Water Clusters Based on an Accurate Value for the Absolute Aqueous Solvation Free Energy of the Proton journal August 2006
Preparation And [2+2] Cycloaddition of 1-Triisopropylsiloxy-1-Hexyne With Methyl Crotonate: 3-Butyl-4-Methyl-2-Triisopropylsiloxy-Cyclobut-2-Enecarboxylic Acid Methyl Ester journal January 2010
Determination of Gibbs free energy of transfer for some univalent ions from water to methanol, acetonitrile, dimethylsulfoxide, pyridine, tetrahydrothiophene and liquid ammonia; standard electrode potentials of some couples in these solvents journal February 1987
Ionic liquids enhance the electrochemical CO 2 reduction catalyzed by MoO 2 journal January 2015
Solubility products and transfer activity coefficients of potassium picrate, potassium tetraphenylborate, and tetraphenylphosphonium picrate in methanol-water mixtures at 25.degree.C journal July 1979
Ionic liquids as electrolytes for Li-ion batteries—An overview of electrochemical studies journal December 2009
Thermodynamic functions of transfer of single ions from water to nonaqueous and mixed solvents: Part 4 - The selection of extra thermodynamic assumptions journal January 1986
Theory of Stationary Electrode Polarography. Single Scan and Cyclic Methods Applied to Reversible, Irreversible, and Kinetic Systems. journal April 1964
Ionic Liquids-Based Extraction: A Promising Strategy for the Advanced Nuclear Fuel Cycle journal December 2011
The “absolute” electrode potential—the end of the story journal January 1990
Deviations from Ideality in Mixtures of Two Ionic Liquids Containing a Common Ion journal March 2005
Absolute Brønsted Acidities and pH Scales in Ionic Liquids journal April 2015
High pressure phase behaviour of mixtures of hydrogen and the ionic liquid family [cnmim][Tf2N] journal January 2013
Voltammetric Characterization of the Ferrocene|Ferrocenium and Cobaltocenium|Cobaltocene Redox Couples in RTILs journal February 2008
Chronoamperometric current at finite disk electrodes journal November 1982