Reline Deep Eutectic Solvent Research Articles

Probing the influence of Zn and water on solvation and dynamics in ethaline and reline deep eutectic solvents by 1H nuclear magnetic resonance.

A range of ethaline and reline deep eutectic solvents (DESs) have been investigated in the absence and presence of Zn (0-0.3 M) and water (0-29 wt%) by one-dimensional 1H NMR spectroscopy, two-dimensional 1H-1H nuclear Overhauser effect and exchange spectroscopy, 1H T1 NMR relaxation times and 1H NMR diffusion. The role of zinc and water in controlling solvation and microstructure in reline and ethaline were investigated. We show that in ethaline there is proton exchange between hydroxyl groups in ethaline glycol and choline chloride. The rate of exchange between these protons is found to significantly increase in the presence of Zn, but decreases with increasing water content. In the case of reline, no proton exchange is observed between the amide protons in urea and hydroxyl protons in choline chloride. However, the addition of water decreases the viscosity of the system, as well as changes the distance between amide and hydroxyl protons in urea and choline chloride, respectively. The addition of Zn does not appear to change the interactions between urea and choline chloride species, but does reduce the rate of exchange between water and hydroxyl protons in reline formulations containing water.

How Pure and Hydrated Reline Deep Eutectic Solvents Affect the Conformation and Stability of Lysozyme: Insights from Atomistic Molecular Dynamics Simulations.

Factors governing the stability and activity of proteins and enzymes in nonaqueous solvents have just been started to be explored. Because of their benign and economically viable nature, deep eutectic solvents (DESs) are being seen as an alternative media in many biotransformation processes. The present study exploits the changes in the conformation and stability of hen egg white lysozyme (HEWL) in the presence of reline (a eutectic mixture of choline chloride and urea) and reline/water mixtures using atomistic molecular dynamics simulations. The lysozyme structure was found to be partially folded in both reline and reline/water mixtures. Root-mean-square deviation (RMSD) of the positions of Cα atoms of lysozyme indicate that 50/50 reline/water solvent induces more destabilization in the conformation of HEWL than that by pure reline and 75/25 reline/water mixture. From the root-mean-square fluctuation (RMSF) analysis, it is found that the lysozyme active site (Glu35-Asp52) is quite stable in the presence of pure reline but it is least stable in the presence of 50/50 reline/water mixture. Our results show that the secondary structure of the lysozyme is significantly affected in the presence of reline. Our further analysis reveals that the hydrogen bonding interaction between HEWL-[Ch]+ dominates over HEWL-urea and HEWL-Cl- in pure reline than in reline/water mixtures.

Effect of temperature on the mechanisms and kinetics of cobalt electronucleation and growth onto glassy carbon electrode using reline deep eutectic solvent

This paper presents insights on the thermodynamics and kinetics of the cobalt electronucleation and growth mechanisms onto glassy carbon electrode from a eutectic mixture of choline chloride and urea. The behavior of the current density transients can be described by a model capable of considering the cobalt three-dimensional nucleation and diffusion-controlled growth from metallic nuclei and the induction-time. Using the proposed model, typical kinetic parameters such as nucleation frequency A, number density of nuclei, N0, and diffusion coefficient, D, were determined at different temperatures and applied potentials. It was found that the residual water has some effects on the early stage of the Co electrodeposition, especially on the nucleation types. Thus, at low temperature it is predominant by progressive nucleation, while at high temperature it is governed by instantaneous nucleation mechanism. Furthermore, from the temperature-dependent relationship of the diffusion coefficient, the Gibbs free energy for cobalt nucleation in DES was able to be estimated.

Molecular dynamics investigation of wetting-dewetting behavior of reline DES nanodroplet at model carbon material.

Deep eutectic solvents (DESs) have emerged as a promising class of solvents for application in nanotechnology, particularly for designing new functional nanomaterials based on carbon. Here, we have employed molecular dynamics simulations to understand the structuring of choline chloride and urea-based DES, reline, nanodroplets on carbon sheets with varying strength of the DES-sheet interaction potentials. The wetting-dewetting nature of reline has been investigated by analyzing simulated contact angles formed by its nanodroplets on the carbon sheets. Through this investigation, we find that at the lowest DES-sheet interaction strength, the contact angle formed by the reline nanodroplet on the carbon surface exceeds 150°, indicating that the surface is supersolvophobic. On the other hand, at the higher interaction potentials, reline DES wets the surface of the sheets, forming an adlayer primarily consisting of urea molecules. The choline cation and urea molecules are observed to exhibit stronger interactions with the carbon surface as compared to that of chloride anions. At the supersolvophobic carbon surface, the urea molecules have relatively higher density in the bulk of the nanodroplet, whereas the choline cation and chloride have major contributions to the outer layers of the droplets. Moreover, at the solvophilic surfaces, urea molecules are present in the adlayer, as well as in the bulk of the droplets, whereas the reline-vapor interface majorly consists of choline and chloride ions.

Electropolymerization of pyrrole from a deep eutectic solvent for supercapacitor applications

In this study, polypyrrole was electroplated onto graphite surface electrochemically from a urea and choline chloride mixture of deep eutectic solvent as the deposition solution. SEM, Raman and FTIR analysis showed that pyrrole was electrochemically polymerized homogeneously as the polypyrrole (PPy) on the graphite surface. Surface morphology of PPy/graphite composite electrode synthesized from the deep eutectic solvent electrolyte medium resembled blistered structures. Electroplated PPy-based composite electrodes were transferred to water containing LiClO4, acetonitrile containing LiClO4 and pure Reline deep eutectic solvent electrolytes to examine their electrochemical properties in different electrolytes. PPy displayed capacitance behavior in all these cycling electrolytes. PPy/graphite composite electrode was reached to 535 F g−1 in aqueous and organic electrolyte. Rate limiting reaction of PPy modified electrodes in three different electrolyte baths is between surface and diffusional controlled mechanism. Electropolymerization of pyrrole from deep eutectic solvent electrolyte media was electrochemically active in three different electrolyte media and is a promising material for supercapacitor applications.

Electrochemical Deposition of Pd@Pd(OH)2 Core-Shell Nanoparticles onto Glassy Carbon from a Deep Eutectic Solvent (Reline) and their Use as Electrocatalyst for the Methanol Oxidation Reaction

Pd@Pd(OH)2 core–shell nanoparticles were potentiostatically electrodeposited onto a glassy carbon electrode, GCE, from Pd(II) ions dissolved in the reline deep eutectic solvent. It is shown that the GCE/Pd@Pd(OH)2-modified electrode displays a high catalytic activity towards the methanol electrochemical oxidation reaction (MOR) in alkaline solution, revealing a mass activity of (2370 ± 450) mA mgPd−1 at the peak potential (for CVs recorded at 0.1 V s−1), much greater than those reported to date for other nanoparticles, namely: Pd, Cu1Pd2, Pd4Ag1, PdFe, PtPdPt, Pt or Pt2Ru1, synthesized by means of technically complicated, expensive and time-consuming methods or electrodeposited from aqueous media. In particular, the steady-state current reported for PdNPs electrodeposited from aqueous media towards MOR depicted values around 3 mA mgPd−1, while those from DES (this work) reached values around 42 mA mgPd−1. Furthermore, it is shown that the Pd@Pd(OH)2 nanoparticles displayed excellent poisoning tolerances, from 2 to 8, depending on the applied potential scan rate and anodic switching potential, which remains practically constant after 200 voltammetric cycles.

Redox characteristics of iron ions in different deep eutectic solvents

Deep eutectic solvents (DESs) have been used as electrolytes in the redox flow battery due to their unique advantages including non-toxicity, biodegradability, and low cost. The most commonly used DESs are the reline DES system (a DES formed from a molar 1:2 mixture of choline chloride and urea) and the ethaline DES system (a DES formed from a molar 1:2 mixture of choline chloride and ethylene glycol). The difference in the component of DES will result in different electrochemical characteristics of the redox couples dissolved therein. In this work, the electrochemical properties of iron ions in ethaline and reline DESs, as well as those of iron ions with FeCl3 and FeCl3·6H2O dissolved in ethaline DES, were experimentally studied. The cyclic voltammetry (CV) results showed that the diffusion coefficient of iron ions in the ethaline DES is greater than that of the reline DES; the redox reversibility of iron ions with FeCl3·6H2O dissolved in ethaline is higher than that of FeCl3 in the same DES, and the reaction rate constant is larger than that of the former, while the diffusion coefficient of the former is slightly smaller than that of the latter. These differences stem from the intrinsic valence discrepancy of FeCl3·6H2O and FeCl3, which is confirmed by the FT-IR spectra analysis. Electrochemical impedance spectroscopy (EIS) also showed that the total resistance in the ethaline solution with FeCl3·6H2O was significantly lower than that with FeCl3. The results of this work can provide key parameters for electrochemical process research and numerical simulation studies on DES.

Influence of Hydration on the Structure of Reline Deep Eutectic Solvent: A Molecular Dynamics Study.

In this article, we have performed an all-atom molecular dynamics simulation study to investigate the influence of water on the molecular level arrangement of reline deep eutectic solvent for different hydration levels ranging from 3.4 to 58.1 wt % of water and complemented the observations of recently measured neutron scattering experimental data. This study is particularly important because water is being introduced as a second hydrogen bond donor/acceptor in reline, wherein the structure is primarily governed by hydrogen bonding and electrostatic interactions. We have analyzed the simulated X-ray scattering structure functions, their partial components, and hydrogen bonding interactions to understand the effects of water on various intermolecular interactions in reline–water mixtures. It is observed that at lower hydration level, reline structure is qualitatively retained. At higher hydration level, most water molecules preferentially solvate chloride anions and ammonium group of choline cations mostly impacting choline–choline, choline–chloride, and chloride–chloride interactions. The present study reveals that at and above 41 wt % of water, the molecular arrangement of reline drastically changes and set to transition from reline to an aqueous solution of reline components with further increase in the hydration level. Hydrogen bond analysis reveals the presence of strong chloride–water H-bonding interaction, which gradually replaces choline–chloride and urea–chloride hydrogen bondings as the hydration level in the mixture increases.

A deep eutectic solvent (DES) electrolyte-based vanadium-iron redox flow battery enabling higher specific capacity and improved thermal stability

Compared with conventional aqueous electrolyte, due to unique merits of deep eutectic solvents including a wide electrochemical window, ease in preparation, low vapor pressure and low cost, they have been used as electrolyte in the non-aqueous flow battery. This work reports a reline deep eutectic solvent, which is prepared as the anolyte and catholyte of a vanadium-iron redox flow battery. Since the solubility of the vanadium and iron species in deep eutectic solvent has been improved, an increased specific capacity can be obtained, up to 54.6% compared with the aqueous electrolyte one. However, the viscosity of this electrolyte is much larger than that of aqueous electrolyte, which causes more pumping losses. With the increase of operating temperature, the viscosity experiences a huge drop. The open-circuit voltage of such an non-aqueous system begins near 0.9 V with a decrease rate of 0.005 V h−1, suggesting a better capacity retention ability than does the aqueous flow battery. The cycling performance of this redox flow battery is evaluated at a current density of 2.0 mA cm−2 under the temperature of 30 °C. The coulombic efficiency is up to 94.8%, while voltage efficiency and energy efficiency are just 68.3% and 64.7%, respectively. The low voltage efficiency stems from the sluggish redox kinetics of the vanadium ions, and large internal ohmic resistance. With an improved thermal stability, this vanadium-iron redox flow battery is preferred to be operated at elevated temperature, which helps to greatly reduce the ohmic loss and pumping loss, such that to increase the system energy efficiency.

Bulk and interfacial structures of reline deep eutectic solvent: A molecular dynamics study.

We apply all-atom molecular dynamics simulations to describe the bulk morphology and interfacial structure of reline, a deep eutectic solvent comprising choline chloride and urea in 1:2 molar ratio, near neutral and charged graphene electrodes. For the bulk phase structural investigation, we analyze the simulated real-space radial distribution functions, X-ray/neutron scattering structure functions, and their partial components. Our study shows that both hydrogen-bonding and long-range correlations between different constituents of reline play a crucial role to lay out the bulk structure of reline. Further, we examine the variation of number density profiles, orientational order parameters, and electrostatic potentials near the neutral and charged graphene electrodes with varying electrode charge density. The present study reveals the presence of profound structural layering of not only the ionic components of reline but also urea near the electrodes. In addition, depending on the electrode charge density, the choline ions and urea molecules render different orientations near the electrodes. The simulated number density and electrostatic potential profiles for reline clearly show the presence of multilayer structures up to a distance of 1.2 nm from the respective electrodes. The observation of positive values of the surface potential at zero charge indicates the presence of significant nonelectrostatic attraction between the choline cation and graphene electrode. The computed differential capacitance (Cd) for reline exhibits an asymmetric bell-shaped curve, signifying different variation of Cd with positive and negative surface potentials.

Synthesis of CuS by elemental-direct-reaction in a reline deep eutectic solvent and its catalytic activity in the thermal decomposition of ammonium perchlorate

Micro-sized copper sulfide (CuS) has been successfully synthesized via an elemental-direct-reaction route in a reline deep eutectic solvent at a low temperature condition (50 °C). The copper sulfide was characterized by X-ray diffraction pattern, scanning electron microscopy images, energy-dispersive X-ray spectroscopy, and transmission electron microscopy. The as-synthesized copper sulfide was pure hexagonal phase microspheres (about 4.0–4.3 μm in diameter), which were assembled with randomly oriented thin slices (about 18 nm in thickness). Moreover, the CuS samples showed high catalytic activity for the thermal decomposition of ammonium perchlorate.

Electrochemical characteristics and transport properties of Fe(II)/Fe(III) redox couple in a non-aqueous reline deep eutectic solvent

Deep eutectic solvent (DES) is a promising electrolyte for non-aqueous redox flow batteries as it offers unique advantages including a wide electrochemical window, low vapor pressure and ease in preparation. In this work, the electrochemical characteristics of the Fe(II)/Fe(III) redox couple and the transport properties of ferric ions in the reline DES are studied. The cyclic voltammetry (CV) curves show that the redox reaction is quasi-reversible with the charge transfer coefficient of 0.44 at room temperature. The diffusivity, viscosity, conductivity of ferric ions in the reline DES are measured at different temperatures. The results indicate that the transport properties are similar to those for conventional ionic liquids. The high solubility of ferric ions in the reline DES is attributed to the formation of hydrogen bond donors, which is confirmed by the FT-IR absorption spectra analysis.