2022

Dynamics of Glyceline and Interactions of Constituents: A Multitechnique NMR Study

Carla C. Fraenza, Ramez A. Elgammal, Mounesha N. Garaga, Sahana Bhattacharyya, Thomas A. Zawodzinski, and Steven G. Greenbaum

Journal of Physical Chemistry B, 126, 4, 890–905, 2022; https://doi.org/10.1021/acs.jpcb.1c09227

The dynamics of the organic components of the deep eutectic solvent glyceline were analyzed using an array of complementary nuclear magnetic resonance (NMR) methods. The results showed that the translational and rotational motions of all species become faster with increasing ChCl concentration up to the eutectic point (33mol% ChCl). This suggests that the glycerol H- bonding network is disrupted as choline is added, but primarily in regions where there is intimate mixing of the two components. Thus, the local dynamics of most of the glycerol resembles that of pure glycerol until substantial choline chloride is present. Moreover, a relatively slow hydroxyl H-exchange process between glycerol and choline protons was deduced from the data.

Evolution of microscopic heterogeneity and dynamics in choline chloride-based deep eutectic solvents

Stephanie Spittle, Derrick Poe, Brian Doherty, Charles Kolodziej, Luke Heroux, Md Ashraful Haque, Henry Squire, Tyler Cosby, Yong Zhang, Carla Fraenza, Sahana Bhattacharyya, Madhusudan Tyagi, Jing Peng, Ramez A Elgammal, Thomas Zawodzinski, Mark Tuckerman, Steve Greenbaum, Burcu Gurkan, Clemens Burda, Mark Dadmun, Edward J Maginn, Joshua Sangoro

Nature Communications, 13, 219, 2022; https://doi.org/10.1038/s41467-021-27842-z

Refined Classical Force Field for Choline Chloride and Ethylene Glycol Mixtures over Wide Composition Range

Yong Zhang, Henry Squire, Burcu Gurkan, and Edward J. Maginn

Journal of Chemical Engineering Data, 2022

https://doi.org/10.1021/acs.jced.1c00841

Studies carried out by BEES and other researchers realized recently that what was believed to be the deep eutectic mixture sometimes is not. For example, it has been accepted that the 1:2 molar ratio of choline chloride (ChCl) and ethylene glycol (EG) is the eutectic point. However, new studies revealed that the eutectic mixture forms at the 1:4 ratio. On the other hand, there is no guarantee that a mixture at the eutectic point has the best properties for optimum electrochemical performance in battery applications. These discoveries clearly demonstrated the urgent need for systematic studies of eutectic solvent mixtures over a wide composition range. Unfortunately, reliable force field for such study is not available. In the current work, the widely used general Amber force field (GAFF) was refined for ChCl and EG mixtures by scaling the atomic partial charges and vdW parameters to fit experimental density and viscosity at multiple compositions. The performance of the refined force field is significantly improved compared to the original model and the calculated density, viscosity, self-diffusion coefficient, and ionic conductivity agree with experiments quantitatively even beyond the fitting compositions and temperatures. This makes it possible to systematically study the liquid properties of the ChCl and EG mixtures as a function of ChCl fraction over a wide composition range. In addition, the procedure used in the current work to refine the ChCl and EG force field can be easily applied to other eutectic liquid mixture systems.

Using the new model, the ionic conductivity of the ChCl and EG mixtures as a function of ChCl mole fraction was studied. It was found that the dynamics in these mixtures with ChCl mole fraction equal to or greater than 20% are similar to that of ionic liquids, high temperature molten salts, and highly concentrated water-in-salt electrolytes. These findings provide new insights of the ion conduction mechanism in these mixtures.

2021

Solvation Dynamics of Wet Ethaline: Water is the Magic Component

Ibrahim Alfurayj, Carla Cecilia Fraenza, Yong Zhang, Rathiesh Pandian, Stephanie Spittle, Bryce Hansen, William Dean, Burcu Gurkan, Robert Savinell, Steve Greenbaum, Edward Maginn, Joshua Sangoro, Clemens Burda

Journal of Physical  Chemistry B, 125, 31, 8888–8901, 2021; https://doi.org/10.1021/acs.jpcb.1c04629

Do Deep Eutectic Solvents Behave Like Ionic Liquid Electrolytes? A Perspective from the Electrode-Electrolyte Interface

William Dean, Jeffrey Klein, Burcu Gurkan

Journal of Electrochemical Society, 168, 026503, 2021; https://doi.org/10.1149/1945-7111/abde83

This study discusses the electrical double layer of choline chloride and ethylene glycol based mixtures (1:2, 1:4, 1:6 molar ratios) including the deep eutectic solvent (DES) ethaline as well as glyceline (1:2 choline chloride:glycerol). Based on the electrochemical impedance spectroscopy (EIS) performed both on gold, platinum and glassy carbon surfaces, the electrode-electrolyte interfaces of DESs is found to be best described by a modified Gouy-Chapman model where only a diffuse layer is assumed with an ion-interaction parameter. The large ion size and the existing H-bonding network in these mixtures prevents the rapid rise in capacitance typical of the classical Gouy-Chapman model, resulting in a shallower U-shaped differential capacitance. This behavior is quite different than ionic liquids (ILs) which are extremely concentrated electrolytes with no neutral solvent molecules. Furthermore, the capacitive behavior of Cl-based DESs present specific ion adsorption on metal surfaces, specifically on gold, Au-Cl complexes form. This work represents one of the earliest srtudies in the field in regards to the theory development for the electrical double layer in DESs which is pertinent to electrochemical kinetics, morphology in electrodeposition processes as well as energy storage.

A Nitroxide Containing Organic Molecule in a Deep Eutectic Solvent for Flow Battery Applications

Nicholas S Sinclair, Derrick Poe, Robert F Savinell, Edward J Maginn, Jesse S Wainright

Journal of Electrochemical Society, 168 020527, 2021; https://doi.org/10.1149/1945-7111/abe28a

The nitroxide radical redox organic molecule, 2-phenyl-4,4,5,5-tetrame- thylimidazoline-1-oxyl-3-oxide (PTIO), was investigated for the first time in a deep eutectic solvent (DES)-like system consisting of a 1:4 molar ratio of choline chloride and ethylene glycol (Ch1EG4) as a redox flow battery electrolyte. PTIO is an attractive redox organic as it is a single molecule with three oxidation states, and can provide both positive and negative redox couples for a flow battery. A flow battery using the PTIO/Ch1EG4 electrolyte demonstrated nearly 50% round trip efficiency with an approximately 1 V open circuit potential. Inefficiencies were primarily due to membrane resistance which can be significantly lowered with increased temperature. While PTIO appears stable over short periods (hours), the oxidized form is not stable in the DES-like electrolyte over longer times. Molecular modeling was performed to investigate the relative stability of PTIO in DES as compared to the previously studied 4-hydroxy-TEMPO (4HT). It was found that the oxoammonium cation 4HT+ exhibits a noticeably larger nucleophilic reactive cloud as compared to PTIO+, indicating a higher reactivity. This method to predict stability of the oxoammonium cation shows promise to inform the design and synthesis of promising redox systems based on nitroxide radicals in DES electrolytes to identify new chemistries for large scale energy storage.

Benworth B Hansen, Stephanie Spittle, Brian Chen, Derrick Poe, Yong Zhang, Jeffrey M Klein, Alexandre Horton, Laxmi Adhikari, Tamar Zelovich, Brian W Doherty, Burcu Gurkan, Edward J Maginn, Arthur Ragauskas, Mark Dadmun, Thomas A Zawodzinski, Gary A Baker, Mark E Tuckerman, Robert F Savinell, Joshua R Sangoro

Chemical Reviews, 121, 3, 1232–1285, 2021; https://doi.org/10.1021/acs.chemrev.0c00385