Solvent Species Research Articles

A Systematic Study on the Effects of Solvating Solvents and Additives in Localized High-Concentration Electrolytes over Electrochemical Performance of Lithium-Ion Batteries.

Localized high-concentration electrolytes (LHCEs) based on five different types of solvents were systematically studied and compared in lithium (Li)-ion batteries (LIBs). The unique solvation structure of LHCEs promotes the participation of Li salt in forming solid electrolyte interphase (SEI) on graphite (Gr) anode, which enables solvents previously considered incompatible with Gr to achieve reversible lithiation/delithiation. However, the long cyclability of LIBs is still subject to the intrinsic properties of the solvent species in LHCEs. Such issue can be readily resolved by introducing a small amount of additive into LHCEs. The synergetic decompositions of Li salt, solvating solvent and additive yield effective SEIs and cathode electrolyte interphases (CEIs) in most of the studied LHCEs. This study reveals that both the structure and the composition of solvation sheaths in LHCEs have significant effect on SEI and CEI, and consequently, the cycle life of energetically dense LIBs.

Quantitative characterization of liquids flowing in geometrically controlled sub-100nm nanofluidic channels.

With development of nanotechnologies, applications exploiting nanospaces such as single-molecule analysis and high-efficiency separation have been reported, and understanding properties of fluid flows in 101nm to 102nm scale spaces becomes important. Nanofluidics has provided a platform of nanochannels with defined size and geometry, and revealed various unique liquid properties including higher water viscosity with dominant surface effects in 102nm spaces. However, experimental investigation of fluid flows in 101nm spaces is still difficult owing to lack of fabrication procedure for 101nm nanochannels with smooth walls and precisely controlled geometry. In the present study, we established a top-down fabrication process to realize fused-silica nanochannels with 101nm scale size, 100nm roughness and rectangular cross-sectional shape with an aspect ratio of 1. Utilizing a method of mass flowmetry developed by our group, accurate measurements of ultra-low flow rates in sub-100nm nanochannels with sizes of 70nm and 100nm were demonstrated. The results suggested that the viscosity of water in these sub-100nm nanochannels was approximately 5 times higher than that in the bulk, while that of dimethyl sulfoxide was similar to the bulk value. The obtained liquid permeability in the nanochannels can be explained by a hypothesis of loosely structured liquid phase near the wall generated by interactions between the surface silanol groups and protic solvent molecules. The present results suggest the importance of considering the species of solvent, the surface chemical groups, and the size and geometry of nanospaces when designing nanofluidic devices and membranes.

Negative and Positive Energetic Elasticity of Polydimethylsiloxane Gels.

We investigated the thermoelasticity of polydimethylsiloxane (PDMS) gels containing six types of solvents with different solubilities. The contribution of energetic elasticity to the total stress (σE/σ) ranges from +0.20 to -0.20 depending on the solvent species. The σE/σ values are positive for the solvents with low molecular mass. By contrast, it is negative for oligodimethylsiloxane (ODMS) or PDMS solvents acting as athermal solvents, each of which has the same chemical structure as the network strands. The investigation using a PDMS rubber without a solvent and the PDMS gels with various ODMS contents reveal a crossover of the σE/σ value from positive to negative with increasing ODMS content. The pronounced dependence of σE/σ on the solvent species and the negative energetic elasticity specific to the high contents of ODMS and PDMS unveil previously unknown aspects of thermoelasticity of polymer gels. The orientation coupling between the segments of the free polymeric chains and network strands is one of the possible scenarios to explain the negative energetic elasticity specific to the ODMS and PDMS solvents, because it stabilizes the aligned state, reducing the elastic energy.

Carbon-Supported and Shape-Controlled PtPd Nanocrystal Synthesis in Flowing Deep Eutectic Solvents for the Methanol Oxidation Reaction

Practical applications of advanced nanocrystals are limited by the lack of low-cost, scalable, and environmentally friendly manufacturing methods with consistent shape and size control. To address this challenge, we demonstrate here the use of continuous-flow reactors and environmentally benign deep eutectic solvents for the shape-controlled synthesis of intermetallic PtPd nanocrystals with almost exclusive octahedral shape and an average size of 12.8 nm within only 6 min of reaction time, much faster than conventional methods. The critical roles of solvent species were elucidated using a family of deep eutectic solvent combinations. We further demonstrate the direct growth of these shaped nanocrystals on carbon using a one-step process by harnessing their strong interactions with a Co- and N-codoped carbon surface, thus avoiding the mandatory additional catalyst separation and loading steps with conventional methods. The produced PtPd nanocrystals exhibited outstanding performance toward the electrooxidation of methanol and reached an activity of 201 mA mg–1 along with improved stability, confirming the promise of our method for scalable and low-cost manufacturing of shape-controlled electrocatalyst materials.

Non-polar ether-based electrolyte solutions for stable high-voltage non-aqueous lithium metal batteries

The electrochemical instability of ether-based electrolyte solutions hinders their practical applications in high-voltage Li metal batteries. To circumvent this issue, here, we propose a dilution strategy to lose the Li+/solvent interaction and use the dilute non-aqueous electrolyte solution in high-voltage lithium metal batteries. We demonstrate that in a non-polar dipropyl ether (DPE)-based electrolyte solution with lithium bis(fluorosulfonyl) imide salt, the decomposition order of solvated species can be adjusted to promote the Li+/salt-derived anion clusters decomposition over free ether solvent molecules. This selective mechanism favors the formation of a robust cathode electrolyte interphase (CEI) and a solvent-deficient electric double-layer structure at the positive electrode interface. When the DPE-based electrolyte is tested in combination with a Li metal negative electrode (50 μm thick) and a LiNi0.8Co0.1Mn0.1O2-based positive electrode (3.3 mAh/cm2) in pouch cell configuration at 25 °C, a specific discharge capacity retention of about 74% after 150 cycles (0.33 and 1 mA/cm2 charge and discharge, respectively) is obtained.

Weak Temperature Dependence of the Relative Rates of Chlorination and Hydrolysis of N2O5 in NaCl–Water Solutions

We have measured the temperature dependence of the ClNO2 product yield in competition with hydrolysis following N2O5 uptake to aqueous NaCl solutions. For NaCl-D2O solutions spanning 0.0054-0.21 M, the ClNO2 product yield decreases on average by only 4 ± 3% from 5 to 25 °C. Less reproducible measurements at 0.54-2.4 M NaCl also fall within this range. The ratio of the rate constants for chlorination and hydrolysis of N2O5 in D2O is determined on average to be 1150 ± 90 at 25 °C up to 0.21 M NaCl, favoring chlorination. This ratio is observed to decrease significantly at the two highest concentrations. An Arrhenius analysis reveals that the activation energy for hydrolysis is just 3.0 ± 1.5 kJ/mol larger than for chlorination up to 0.21 M, indicating that Cl- and D2O attack on N2O5 has similar energetic barriers despite the differences in charge and complexity of these reactants. In combination with the measured preexponential ratio favoring chlorination of 300-200+400, we conclude that the strong preference of N2O5 to undergo chlorination over hydrolysis is driven by dynamic and entropic, rather than enthalpic, factors. Molecular dynamics simulations elucidate the distinct solvation between strongly hydrated Cl- and the hydrophobically solvated N2O5. Combining this molecular picture with the Arrhenius analysis implicates the role of water in mediating interactions between such distinctly solvated species and suggests a role for diffusion limitations on the chlorination reaction.

Interface Engineering with Nonsacrificial Perfluorinated-Anion Additives for Boosting the Kinetics of Lithium-Ion Batteries.

Though lithium-ion batteries (LIBs) have seen a meteoric rise in worldwide deployment over the last decade, they should be further advanced in constant demand of higher rate capability and wider temperature adaptability. A solid electrolyte interphase (SEI) is the essential part of LIBs, determining the charge-discharge performance and degradation behavior. Herein, improvement of the SEI properties is achieved by regulating the electrochemical double layer structure with a nonsacrificial electrolyte additive, that is, lithium nonafluoro-1-butanesulfonate. The anion adsorption of the additive affects the decomposition behavior of other additive and solvent species, and the generated SEI at the graphite electrode becomes thinner and more uniform, leading to decreased impedance and finally resulting in improved energy efficiency, power capability, and fast charging performance of the graphite/NCM811 cell. Furthermore, the low-temperature cycleability at -20 °C is considerably enhanced with no dendritic Li metal deposition at the negative electrode surface. A mechanistic study on the interfacial phenomena and the effect is carried out by using various theoretical and experimental methods, such as density functional theory calculations, electrochemical quartz crystal microbalance, and transmission electron microscopy. Consequently, the approach of SEI modification with the nonsacrificial electrolyte additive can be one of the effective ways to advance LIB technology in future.

Measurement and correlation of diffusion coefficients of vitamin K3 in a fluid mixture of carbon dioxide and decane at 313–343 K and 10–30 MPa

The diffusion coefficients D1m of vitamin K3 in a dense fluid mixture of carbon dioxide and decane were measured by the Taylor dispersion method at temperatures from (313.2–343.2) K and pressures from (10−30) MPa, over the entire range of decane composition. The D1m values of vitamin K3 increased with increasing temperature and decreasing pressure under isocratic conditions. In addition, the measured D1m values were found to be correlated with the hydrodynamic (HD) equation based on the Stokes–Einstein equation, with an average relative deviation of 4.9% for 110 conditions over a wide range of fluid viscosities ranging from that of supercritical carbon dioxide to that of compressed liquid decane, apparently irrespective of the decane composition and solvent species.

Coordination-Dependent Chemical Reactivity of TFSI Anions at a Mg Metal Interface

Charge transfer across the electrode-electrolyte interface is a highly complex and convoluted process involving diverse solvated species with varying structures and compositions. Despite recent advances in in situ and operando interfacial analysis, molecular specific reactivity of solvated species is inaccessible due to a lack of precise control over the interfacial constituents and/or an unclear understanding of their spectroscopic fingerprints. However, such molecular-specific understanding is critical to the rational design of energy-efficient solid-electrolyte interphase layers. We have employed ion soft landing, a versatile and highly controlled method, to prepare well-defined interfaces assembled with selected ions, either as solvated species or as bare ions, with distinguishing molecular precision. Equipped with precise control over interfacial composition, we employed in situ multimodal spectroscopic characterization to unravel the molecular specific reactivity of Mg solvated species comprising (i.e., bis(trifluoromethanesulfonyl)imide, TFSI-) anions and solvent molecules (i.e., dimethoxyethane, DME/G1) on a Mg metal surface relevant to multivalent Mg batteries. In situ multimodal spectroscopic characterization revealed higher reactivity of the undercoordinated solvated species [Mg-TFSI-G1]+ compared to the fully coordinated [Mg-TFSI-(G1)2]+ species or even the bare TFSI-. These results were corroborated by the computed reaction pathways and energy barriers for decomposition of the TFSI- within Mg solvated species relative to bare TFSI-. Finally, we evaluated the TFSI reactivity under electrochemical conditions using Mg(TFSI)2-DME-based phase-separated electrolytes representing different solvated constituents. Based on our multimodal study, we report a detailed understanding of TFSI- decomposition processes as part of coordinated solvated species at a Mg-metal anode that will aid the rational design of improved sustainable electrochemical energy technologies.

Impact of Hydrophobic Chains in Five-Coordinate Glucoconjugate Pt(II) Anticancer Agents.

This study describes new platinum(II) cationic five-coordinate complexes (1-R,R') of the formula [PtR(NHC)(dmphen)(ethene)]CF3SO3 (dmphen = 2,9-dimethyl-1,10-phenanthroline), containing in their axial positions an alkyl group R (methyl or octyl) and an imidazole-based NHC-carbene ligand with a substituent R' of variable length (methyl or octyl) on one nitrogen atom. The Pt-carbene bond is stable both in DMSO and in aqueous solvents. In DMSO, a gradual substitution of dmphen and ethene is observed, with the formation of a square planar solvated species. Octanol/water partitioning studies have revealed the order of hydrophobicity of the complexes (1-Oct,Me > 1-Oct,Oct > 1-Me,Oct > 1-Me,Me). Their biological activity was investigated against two pairs of cancer and non-cancer cell lines. The tested drugs were internalized in cancer cells and able to activate the apoptotic pathway. The reactivity of 1-Me,Me with DNA and protein model systems was also studied using UV-vis absorption spectroscopy, fluorescence, and X-ray crystallography. The compound binds DNA and interacts in various ways with the model protein lysozyme. Remarkably, structural data revealed that the complex can bind lysozyme via non-covalent interactions, retaining its five-coordinate geometry.

Size-modified Poisson–Nernst–Planck approach for modeling a local electrode environment in CO2electrolysis

A continuum-scale model for CO2ER is presented, including steric effects of both solute and solvent species along with Frumkin-corrected kinetics. The model gives accurate concentration profiles and experimentally verifiable current density results.

Direct thermal catalytic synthesis of hydrogen peroxide by using microchip reactor

Direct synthesis of hydrogen peroxide (H2O2) from hydrogen and oxygen (DSHP) represents a promising alternative route to the current widely used anthraquinone process, as the latter has been much criticized for not-environmentally friendly issue. However, most DHSP reaction systems encounter with the challenge of explosion risk and low-selective for production of H2O2. Herein, we report a new continuous DSHP process by constructing a feasible microreactor upon microfluidic chip under ambient condition. By examining the effects of temperature, liquid flow rate, gas flow rate, H2/O2 ratio and solvent species on the production rate of H2O2, we demonstrated that the methanol is the most favorable solvent for promoting the DSHP process, and further identified the optimal reaction condition under which continuous production of H2O2 with the concentration of 0.388 wt% is achieved. Additionally, the DFT calculations were performed, which unraveled the solvent effect and showed that the methanol molecule can efficiently stabilize the O2 molecule and co-catalyze the DSHP reaction. Finally, the economic analysis of the proposed process is carried and compared with the commercial ones. This work provides a promising on-site route to produce H2O2 in a green, safe yet ready-to-use process.

Ursolic Acid and Oleanolic Acid Dissolved in Methanol/Acetone + Water Blends: Thermodynamic Solubility, Intermolecular Interactions, and Solvation Behavior

With the purpose of qualitative characterization of the electrostatic properties of the acidity and basicity of ursolic acid (UA) and oleanolic acid (OA), quantitative analyses of the molecular surface were employed in this contribution. The −OH and −COOH groups on the molecules of OA and UA took precedence over establishing hydrogen bonds with the solvents acetone/methanol/water. In addition, the intermolecular interactions of OA and UA with acetone/methanol/water were investigated using an independent gradient model based on the Hirshfeld partition of molecular density. In solutions of OA/UA dissolved in methanol/acetone/water, attractive interactions, including the hydrogen-bond force and van der Waals (vdW) force, occur. The shake-flask technique was applied to evaluate the equilibrium solubility of UA and OA in acetone + water and methanol + water at 101.2 kPa and elevated temperatures covering from 278.15 to 323.15 K. Solvent–solvent interactions accounted by the solubility parameter of solutions had a significant domination in the variability of solubility magnitudes. The van’t Hoff–Jouyban–Acree, Apelblat, and Jouyban–Acree models revealed a good correlation for the measured solubility, with a relative mean deviation of no more than 7.73%. The Kirkwood–Buff integral approach was utilized to determine the preferred solvation of UA and OA by solvent species. In both the rich- and intermediate-composition regions of methanol/acetone, UA or OA is preferentially solvated with positive preferential solvation parameters by methanol/acetone.

Spectroscopic investigations of solvent assisted Li-ion transport decoupled from polymer in a gel polymer electrolyte

We present here a gel polymer electrolyte, where the Li+-ion transport is completely decoupled from the polymer host solvation and dynamics. A free-standing gel polymer electrolyte with a high volume content (nearly 60%) of xM LiTFSI in G4 (tetraglyme) (x = 1–7; Li+:G4 = 0.2–1.5) liquid electrolyte confined inside the PAN (polyacrylonitrile)-PEGMEMA [poly (ethylene glycol) methyl ether methacrylate oligomer] based polymer matrix is synthesized using a one-pot free radical polymerization process. For LiTFSI concentrations, x = 1–7 (Li+:G4 = 0.2–1.5), Raman and vibrational spectroscopies reveal that like in the liquid electrolyte, the designed gel polymer electrolytes (GPEs) also show direct coordination of Li+-ions with the tetraglyme leading to the formation of [Li(G4)]+. Coupled with the spectroscopic studies, impedance and nuclear magnetic resonance investigations also show that the ion transport is independent of the polymer segmental motion and is governed by the solvated species {[Li(G4)]+}, very similar to the scenario in ionic liquids. As a result, the magnitude of ionic conductivity and activation energies of the gel polymer electrolyte are very similar to that of the liquid electrolyte. The Li+-ion transport number for the GPE varied from 0.44 (x = 1) to 0.5 (x = 7) with the maximum being 0.52 at x = 5.

Ultra-fast microwave-assisted synthesis of photoluminescent carbon dots with an ultra-high quantum yield for H2O2 detection

The conventional hydrothermal bottom-up synthesis for preparing carbon dots (CDs) usually requires stringent conditions and high energy consumption, whereas the quantum yield (QY) of CDs remains at a relatively low level. Herein, CDs exhibiting strong blue photoluminescence (PL) with an ultra-high QY (up to 94.4%) were prepared via a simple one-step microwave-assisted route using citric acid (CA) and o-phenylenediamine (o-PD) as precursors. The operating conditions, including reaction time, solvent species, amount of solvent, and precursor molar ratio, were optimized. The CDs synthesized within 3.5 min of microwave heating in ethylene glycol (EG) at a CA-to-PD molar ratio of 5:1 exhibited the highest QY (94.4%). A synergistic PL mechanism of the molecule state and carbon core state emissive centers was proposed according to the characterization results of CDs. Moreover, the proof-to-concept H2O2 fluorescent detection performances of the prepared CDs confirmed their great application potential as probe materials. Through directly mixing the CD products and H2O2, a strong PL response could be rapidly detected after merely 1 min, and the detection limit was calculated to be as low as 8.6 nM. Besides, the CDs exhibited high biocompatibility, making them suitable for in-vivo detection of H2O2. Therefore, this work provides a novel and efficient approach for synthesis of ultra-high QY CDs that can be directly applied in biological detection.

Photophysical evaluation on the electronic properties of synthesized biologically significant pyrido fused imidazo[4,5-c]quinolines

A single pot microwave assisted method was employed to synthesize a series of novel pyrido fused imidazo[4,5-c]quinolines. The electronic properties of these derivatives were investigated by following their photophysical behaviour under isolated and solvated conditions via computational and experimental approaches. The solvatochromic effect of these derivatives was investigated in the ground and excited singlet states by following the absorption and fluorescence emission and excitation spectra. Further the effect of general and specific solvent effects were also investigated by plotting Stokes shift against Lippert-Mataga, ET(30) and Kamlet-Taft polarity parameters respectively. The deviation from linearity in ET(30) plot indicates that formation of different species in polar protic solvents. The biological applications of these derivatives as potential drug candidates were evaluated by in silico computational methods followed by pharmacokinetic properties predictions. The ability of these derivatives to inhibit human casein kinase 2 (CK2) was evaluated. The structure activity relationships were correlated by evaluating the electronic properties through experimental photophysical investigations including solvatochromic effect and computational electronic structure calculations. Of the various derivatives, p-nitro phenyl substituted pyrido fused imidazo[4,5-c]quinoline exhibited good inhibitory activity against CK2 enzyme and hence could serve as a promising drug candidate.

Effect of TBP on the Coordination Process of Eu(III) with T2EHDGA: A Luminescence Spectroscopy Investigation

AbstractIn this report, we explore the precise responsibility of a phase modifier along with the prime ligand in the coordination process of Ln(III) ions using luminescence spectroscopic technique by taking Eu(III) as the probeing metal ion. A well accepted diglyoclamide (DGA) ligand: N,N,N’,N’‐ tetra(ethylhexyl)diglycolamide(T2EHDGA) was used as the prime extractant along with tri‐n‐butylphosphate (TBP) as the phase modifier. Meticulous investigations on Eu(III) complexation with T2EHDGA‐TBP binary mixture was pursued by employing luminescence spectroscopy with the systematic variation of the concentration of TBP in the ligating phase and initial concentration of Eu(III) in the feed phase. The dominancy of the LMCT band over that of the metal centered band signifies the structural difference in the ligands used in the study. The presence of TBP in the organic phase enhances the intensity of 5D0→7F2 and 5D0→7F0 transition. The excitation and emission patterns of the Eu(III)‐solvate species formed in the organic phase both in unirraditaed and irradiated conditions were found to be entirely different, which effectively corroborates the efficacy of the extracting phase. The asymmetry ratio (AR) and the life time data at each experimental conditions were ascertained to realize the coordination behavior of the Eu(III) complex in the organic phase.

Linear orthobaric-density approach to the Krichevskii parameter of a solute from its vapor-liquid distribution coefficient: What can we learn about its accuracy from systems whose precise behavior is known?

We invoke the thermodynamic description of the solvation behavior of two limiting-case model solutes in highly-compressible environments of a real solvent to address the issue identified in the subtitle of this manuscript. We probe the effect of small experimental uncertainties in the vapor-liquid distribution constant of a dilute solute on the regressed limiting orthobaric-density slope by interrogating how this slope deviates from the theoretically-expected known values. The approach becomes feasible because we have developed the solvation thermodynamics of two limiting-case solute-solvent intermolecular asymmetries, i.e., the ideal gas solute and the solute behaving as another real solvent species, whose exact results provide unambiguous answers. We also uncover the non-monotonic dependence of the orthobaric-density slope of the vapor-liquid distribution constant involving the ideal gas solute in either light- or heavy-water solutions, a behavior that conspires against the key hypothesis behind the linear regression approach and the accuracy of the resulting Krichevskii parameters. Moreover, we reveal the significant water H/D−substitution effect on the orthobaric-density range of validity of the linear density representation for the vapor-liquid distribution constant of a solute.

Shifting the Triangle-Square Equilibrium of Self-Assembled Metallocycles by Guest Binding with Enhanced Photosensitization.

Shifting a triangle-square equilibrium in one direction is an important problem in supramolecular self-assembly. Reaction of a benzothiadiazole-based diimidazole donor with a cis-Pt(II) acceptor yielded an equilibrium mixture of a triangle ([C18H24N10O6S1Pt1]3≡ PtMCT) and a square ([C18H24N10O6S1Pt1]4≡ PtMCS). We report here the shifting of such equilibrium toward a triangle using a guest (pyrene aldehyde, G1). While both benzothiadiazole and pyrene aldehyde can form reactive oxygen species (ROS) in organic solvents, their therapeutic use in water is restricted due to aqueous insolubility. The enhanced water solubility of the benzothiadiazole unit and G1 by macrocycle formation and host-guest complexation, respectively, enabled enhanced ROS generation by the host-guest complex (G1' ⊂ PtMCT) in water (G1' = hydrated form of G1). The guest-encapsulated metallacycle (G1' ⊂ PtMCT) has shown synergistic antibacterial activity compared to the mixture of macrocycles upon white-light irradiation due to enhanced ROS generation. The mechanism for such enhanced activity was established by measuring the oxidative stress and relative internalization of PtMCs and G1' ⊂ PtMCT.

Ion Solvation Free Energy Calculation Based on Ab Initio Molecular Dynamics Using a Hybrid Solvent Model.

Free energy calculation of small molecules or ion species in aqueous solvent is one of the most important problems in electrochemistry study. Although there are many previous approaches to calculate such free energies, they are based on ab initio methods and suffer from various limitations and approximations. In the current work, we developed a hybrid approach based on ab initio molecular dynamics (AIMD) simulations to calculate the ion solvation energy. In this approach, a small water cluster surrounding the central ion is used, and implicit solvent model is applied outside the water cluster. A dynamic potential well is used during AIMD to keep the water cluster together. Quasi-harmonic approximation is used to calculate the entropy contribution, while the total energy average is used to calculate the enthalpy term. The obtained solvation voltages of the bulk metal agree with experiments within 0.3 eV, and the simulation results for the solvation energies of gaseous ions are close to the experimental observations. Besides the free energies, radial pair distribution functions and coordination numbers of hydrated cations are also obtained. The remaining challenges of this method are also discussed.