High Dielectric Medium Research Articles

Improving the optoelectronic properties of monolayer MoS2 field effect transistor through dielectric engineering

The reduced dielectric screening in atomically thin two-dimensional materials makes them very sensitive to the surrounding environment, which can be modulated to tune their optoelectronic properties. In this study, we significantly improved the optoelectronic properties of monolayer MoS2 by varying the surrounding environment using different liquid dielectrics, each with a specific dielectric constant ranging from 1.89 to 18. Liquid mediums offer the possibility of environment tunability on the same device. For a back-gated field effect transistor, the field effect mobility exhibited more than two-order enhancement when exposed to a high dielectric constant medium. Further investigation into the effect of the dielectric environment on the optoelectronic properties demonstrated a variation in photoresponse relaxation time with the dielectric medium. The rise and decay times were observed to increase and decrease, respectively, with an increase in the dielectric constant of the medium. These results can be attributed to the dielectric screening provided by the surrounding medium, which strongly modifies the charged impurity scattering, the band gap, and defect levels of monolayer MoS2. These findings have important implications for the design of biological and chemical sensors, particularly those operating in a liquid environment. By leveraging the tunability of the dielectric medium, we can optimize the performance of such sensors and enhance their detection capabilities.

Exploring the Microscopic Aspects of 1-Methyl-3-octylimidazolium Tetrafluoroborate Mixtures with Formamide, N-Methylformamide, and N,N-Dimethylformamide by Multiple Spectroscopic Techniques and Computations.

The microscopic aspects of 1-methyl-3-octylimidazolium tetrafluoroborate ([MOIm][BF4]) mixtures with formamide (FA), N-methylformamide (NMF), and N,N-dimethylformamide (DMF) were investigated using spectroscopic techniques of femtosecond Raman-induced Kerr effect spectroscopy (fs-RIKES), FT-IR, and NMR. Molecular dynamics simulations and quantum chemistry calculations were also performed. According to fs-RIKES, the first moment of the low-frequency spectrum bands mainly originating from the intermolecular vibrations in the [MOIm][BF4]/FA and [MOIm][BF4]/DMF systems changed gradually with the molecular liquid mole fraction XML but that in the [MOIm][BF4]/NMF system was constant up to XNMF = 0.7 and then gradually increased in the range of XNMF ≥ 0.7. Excluding the contribution of the 2D hydrogen-bonding network due to the presence of FA in the low-frequency spectrum band, the XML dependence of the normalized first moment of the low-frequency band in the [MOIm][BF4]/FA and [MOIm][BF4]/NMF systems revealed that the normalized first moment did not remarkably change in the range of XML < 0.7 but drastically increased in XML ≥ 0.7. FT-IR results indicated that the amide C═O band shifted to the low-frequency side with increasing XML for the three mixtures due to the hydrogen bonds. The imidazolium ring C-H band also showed a similar tendency to the amide C═O band. 19F NMR probed the microenvironment of [BF4]- in the mixtures. The [MOIm][BF4]/NMF and [MOIm][BF4]/DMF systems showed an up-field shift of the F atoms of the anion with increasing XML, and the [MOIm][BF4]/FA system exhibited a down-field shift. Steep changes in the chemical shifts were confirmed in the region of XML > 0.8. On the basis of the quantum chemistry calculations, the observed chemical shifts with increasing XML were mainly attributed to the many-body interactions of ions and amides for the [MOIm][BF4]/FA and [MOIm][BF4]/DMF systems. Meanwhile, the long distance between the cation and the anion was due to the high dielectric medium for the [MOIm][BF4]/NMF system, which led to an up-field shift.

Effect of polyol type on the structure and properties of lecithin liposomes prepared using the polyol dilution method

The polyol dilution (PD) method is an approach for preparing liposomes by pre-mixing a lipid/polyol binary mixture, followed by hydration, and is widely used in the cosmetics industry. In this method, polyols play an important role in the formulation design and application, however, the effect of the polyol type on liposomes (PD-liposomes) is yet to be understood. In this study, we investigated the effect of three types of polyols—glycerol (Gly), propylene glycol (PG), and 1,3-butylene glycol (BG)—on the physicochemical properties of PD-liposomes composed of hydrogenated egg yolk lecithin (EL). The particle size of PD-liposomes was controlled by adjusting the type and concentration of the polyols. Furthermore, the addition of polyols improved the dispersion stability, indicating that PD-liposomes are suitable for industrial applications. The morphology of lipid/polyol binary mixture was the determining factor of the liposome structure, and the formation region of unilamellar vesicles (ULVs) and multilamellar vesicles (MLVs) was closely related to the dielectric constant of the dispersion medium. ULVs were formed using a high dielectric constant dispersion medium, such as Gly, and MLVs were formed using a low dielectric constant dispersion medium, such as PG and BG at high concentrations. This study showed that the addition of polyols improves the phase homogeneity of the bilayer and that PG or BG is more effective than Gly. The control of the homogeneity of the bilayer phase is an effective technique to prevent leakage and control the sustained release of the active ingredient; thus, this method enhances the efficacy of the active ingredient. This study is the first to systematically elucidate the control mechanisms of the physicochemical properties of PD-liposomes, including the particle size, dispersion stability, shape, and phase state of the bilayer. Our findings will contribute to the wide range of applications of PD-liposomes.

Probing Electrolyte Influence on CO2 Reduction in Aprotic Solvents

Selective CO2 capture and electrochemical conversion are important tools in the fight against climate change. Industrially, CO2 is captured using a variety of aprotic solvents due to their high CO2 solubility. However, most research efforts on electrochemical CO2 conversion use aqueous media and are plagued by competing hydrogen evolution reaction (HER) from water breakdown. Fortunately, aprotic solvents can circumvent HER, making it important to develop strategies that enable integrated CO2 capture and conversion. However, the influence of ion solvation and solvent selection within nonaqueous electrolytes for efficient and selective CO2 reduction is unclear. In this work, we show that the bulk solvation behavior within the nonaqueous electrolyte can control the CO2 reduction reaction and product distribution occurring at the catalyst–electrolyte interface. We study different tetrabutylammonium (TBA) salts in two electrolyte systems with glyme ethers (e.g., 1,2 dimethoxyethane or DME) and dimethyl sulfoxide (DMSO) as a low and high dielectric constant medium, respectively. Using spectroscopic tools, we quantify the fraction of ion pairs that forms within the electrolyte. Also, we show how ion pair formation is prevalent in DME and is dependent on the anion type. More importantly, we show that as ion pair formation decreases within the electrolyte, CO2 current densities increase, and a higher CO Faradaic efficiency is observed at low overpotentials. Meanwhile, in an electrolyte medium where the ion pair fraction does not change with the anion type (such as in DMSO), a smaller influence of solvation is observed on CO2 current densities and product distribution. By directly coupling bulk solvation to interfacial reactions and product distribution, we showcase the importance and utility of controlling the reaction microenvironment in tuning the electrocatalytic reaction pathways. Insights gained from this work will enable novel electrolyte designs for efficient and selective CO2 conversion to desired fuels and chemicals.

A compact and miniaturized implantable antenna for ISM band in wireless cardiac pacemaker system

A tiny and compact implantable antenna for wireless cardiac pacemaker systems is designed. The antenna works in the Industrial Scientific Medical (ISM) frequency band (2.4–2.48 GHz). The size of the antenna is greatly reduced with the adoption of a high dielectric constant medium and a folded meander structure. The volume of the antenna is 4.5 mm3, and the size is only 3 mm × 3 mm × 0.5 mm. Based on the literature research, it was found that the design was the smallest among the same type of implanted antenna. The antenna is optimized and loaded with a defective slotted structure, which improves the efficiency of the overall performance of the antenna and thus the gain thereof. The antenna maintains good impedance matching in the ISM frequency band, covering the entire ISM frequency band. The actual bandwidth of the antenna is 22%, with the peak gain of − 24.9 dBi. The antenna is processed and manufactured in such a manner that the simulation keeps consistent with the actual measurement. In addition, the specific absorption rate of the antenna is also evaluated and analyzed. The result shows that this kind of antenna is the best choice to realize the wireless biological telemetry communication in the extremely compact space of the wireless cardiac pacemaker system.

Computing Protein pKas Using the TABI Poisson–Boltzmann Solver

A common approach to computing protein pKas uses a continuum dielectric model in which the protein is a low dielectric medium with embedded atomic point charges, the solvent is a high dielectric medium with a Boltzmann distribution of ionic charges, and the pKa is related to the electrostatic free energy which is obtained by solving the Poisson–Boltzmann equation. Starting from the model pKa for a titrating residue, the method obtains the intrinsic pKa and then computes the protonation probability for a given pH including site–site interactions. This approach assumes that acid dissociation does not affect protein conformation aside from adding or deleting charges at titratable sites. In this work, we demonstrate our treecode-accelerated boundary integral (TABI) solver for the relevant electrostatic calculations. The pKa computing procedure is enclosed in a convenient Python wrapper which is publicly available at the corresponding author’s website. Predicted results are compared with experimental pKas for several proteins. Among ongoing efforts to improve protein pKa calculations, the advantage of TABI is that it reduces the numerical errors in the electrostatic calculations so that attention can be focused on modeling assumptions.

Effects of Ion Size and Dielectric Constant on Ion Transport and Transference Number in Polymer Electrolytes

Salt-doped polymers without added solvents have the potential to be nonflammable, robust electrolytes for batteries but suffer from low ion conductivity. Using bulky anions with delocalized charge may reduce ion agglomeration and increase conduction. However, size asymmetry between ions may increase preferential solvation of cations versus the larger anions, lowering the transference number t+ (fraction of conductivity contributed by the cation, relevant to battery performance). We use coarse-grained molecular dynamics simulations, including a 1/r4 potential to capture size-dependent solvation effects, to relate polymer and ion chemistry to t+ and overall conductivity. At low ion size disparity, increasing dielectric constant improves cation conduction due to the mitigation of ion aggregation and correlated cation–anion motion. However, at high ion size disparity, high dielectric medium results in strong preferential solvation of cations, reducing cation mobility and t+. The trade-off between better cation–anion separation and cation preferential solvation suggests that the strategy of developing high dielectric polymers may enhance performance only at low ion size disparity.

Controllable Filtering Structure Using Magnetic Coupling Between Spoof Plasmonic Waveguide and Solid Dielectric Resonators

The structure and electrical characteristics of a dielectric resonator (abbreviated as DR hereafter) loaded plasmonic waveguide with controllable bandwidth are investigated in the present research. By loading the high permittivity dielectric medium on a spoof surface plasmonic waveguide, the working bandwidth of the filtering structure can be regulated flexibly due to the resonant effect of the loaded cylindrical DR. The DR is home-made and possesses the permittivity of 25.66, tanδ of 5.3 × 10 -5 and stable temperature coefficient of -6.3 ppm/°C in microwave region. After the DR is loaded, the filtering structure can form the transmission zero on the edge of the pass band, regulating the bandwidth as well as increasing the out-of-band rejection. By controlling the height between the loaded DR and the substrate, or adjusting the inter-distance between the DRs, the relative bandwidth of the filtering structure can be effectively tailored.

A Passive UHF RFID Dielectric Sensor for Aqueous Electrolytes

The one-step modification of a commercial RFID sensing tag is demonstrated using polydimethylsiloxane-based thin-film chemistry to construct reusable passive RFID sensors for changes in the dielectric properties of electrolyte solutions as a function of concentration. The effects of PDMS film thickness were characterized as a function of RFID sensor code value. The output sensor code of the RFMicron RFM2100-AER wireless flexible moisture sensor (taken between 800 and 860 MHz) was compared with the readings taken when the tag was dry and when the tag had a water deposition on the sensor area. The effect of the direct application of liquid water on the tag was to alter the capacitance presented to the integrated chip which auto-tunes to correct for the reactance. By varying the thickness of the PDMS film between the interdigitated sensor and deposited liquid, the sensitivity of the tag to a high dielectric medium could be controlled. Aqueous salt solutions were tested on a 500-μm-thick film. It was found that the sensing platform could be used as a means of measuring the concentration of various salt solutions within the range 0–2 M and in turn could be used as a passive UHF RFID dielectric measuring tool. The measurement capability of the platform was subsequently demonstrated using a reduced frequency range (845–865 MHz).

Conformational Equilibria of Multimodal Chromatography Ligands in Water and Bound to Protein Surfaces.

Multimodal chromatography uses small ligands with multiple modes of interaction, e.g., charged, hydrophobic or hydrogen bonding, to separate proteins from complex mixtures. The mechanism by which multimodal ligands interact with proteins is expected to be affected by ligand conformations, among other factors. Here, we study conformational equilibria of two commercially used multimodal cation exchange ligands, Capto MMC and Nuvia cPrime, in a range of solvents, a Lennard-Jones (LJ) liquid, ethanol, and water, using molecular dynamics (MD) simulations. By mapping ligand conformations onto two key torsion angles, ω and φ, in these solvents and in low and high dielectric media, we quantify the relative importance of intramolecular and solvent-mediated interactions. In a high dielectric medium, Capto MMC preferentially samples three conformations, which are stabilized by a combination of an intramolecular torsion potential (on ω) and LJ interactions. In an LJ liquid, solvent molecules compete with intramolecular interactions while simultaneously providing an osmotic force, stabilizing both closer and farther distances between ligand sites. This has the overall effect of "flattening out" the conformational landscape. Interestingly, in ethanol and water, hydrogen bonding between the amide hydrogen and solvent molecules stabilizes two additional conformations of Capto MMC in which ω takes on less favorable cis-like configurations. MD simulations of ligands in free solution with three therapeutic antibody fragments show that ligand conformational equilibria remain effectively unchanged upon binding to proteins. Although, there is 20-30% dehydration of the overall ligand upon binding, the hydrogen-bonding sites are dehydrated to a much smaller extent, particularly in cis-like configurations. Conformational preferences of Nuvia cPrime are similar to that of Capto MMC, except for the effect of symmetry arising from the absence of an alkyl thiol tail. Characterizing the conformational equilibria of these two ligands in free solution and bound to a protein provides a foundation for developing a mechanistic understanding of protein-multimodal ligand interactions.

Determining the Regimes of Dielectric Mismatch and Ionic Correlation Effects in Ionomer Blends

We examine the effects of ionic correlations and dielectric mismatch on the miscibility of ionomer blends with a hybrid ionomer blend thermodynamic liquid state theory approach. The ionomer (A) has a dielectric constant ϵA and low charge fraction (<10%). First, explicit ions coarse-grained molecular dynamics simulations with no dielectric mismatch verify that ionic correlations lead to segregation, in agreement with the theory, which includes nonlinear and many-body effects. Then, the extended theory that incorporates dielectric mismatch shows that strong ionic correlations dominate the phase behavior when the dielectric mismatch is low. However, solvation effects dominate when the mismatch is high (ϵA ≫ ϵB), where the preference of the ions to be solvated in a higher dielectric medium is balanced by the entropic driving force for a uniform dielectric constant throughout the system. When salt is added as a third component, dielectric mismatch is significant only at low salt concentrations.

Multinuclear magnetic resonance investigation of cation-anion and anion-solvent interactions in carbonate electrolytes

The investigation of ion-solvent interaction in electrolytes is crucial for basic understanding of ion transport through the bulk electrolyte as well as interphase formation processes on both electrodes, which dictate performances of lithium ion batteries (LIBs). In this report, nuclear magnetic resonance (NMR) was used to study the solvation behaviors of two typical lithium salts (lithium hexafluorophosphate, or LiPF6, and lithium tetrafluoroborate, or LiBF4) dissolved in ethylene carbonate (EC)/dimethyl carbonate (DMC) mixtures. With increasing salt concentration and DMC percentage in both systems, 19F NMR experiences an upfield shift along with decreasing J31P−19F and J11B−19F, which evidence the stronger interaction between the Li+ and F− in an environment with diminishing presence of high dielectric medium. The quadrupolar relaxation of 11B dominates the 19F relaxation mechanism and demonstrates that LiBF4 mainly exists as ion pairs in solution either at high salt concentration or in a medium of low polarity. 7Li, 19F, 1H NMR diffusion measurements were conducted to characterize the relative mobility of cation, anion and solvent molecules, the results of which support the conclusion above. Salt concentration and solution polarity have a much stronger effect on cation-anion aggregation and solvation in the LiBF4 system than in the LiPF6 system.

(Invited) Polymer Simulations Under External Fields

In order to design next generation functional polymers, not only the structure but the dynamics under external field should be understood. In this paper we report our simulation approach to investigate the structure and dynamics. Polymer brush is used for the model system of very low friction such as synovial joints. Recently, polymer brush is focused as a functional binder of sodium ion secondary battery. Since sodium ions are hard to make passive film, or SEI (solid electrolyte interphase) layer on the negative electrode, functional polymer binder help to stabilize the atmosphere around the electrode. We simulate the ionic conductivity of polyelectrolyte binder system under external electric field. The conductivity depend on the polymer structure, such as hardness and linear charge density of the polymer chain. The other important function of polymers are the fluid dynamics effect of polymers under external fluid field. As a model system of VII (viscosity index improver) polymers, we simulate the dynamics under shear filed. The dynamics of polymers are studied for bulk system and the confined system. We made simulation algorithm. The Brownian motion of polymer segments are treated by Langevin Dynamics, and the solvent flow is treated by Lattice Boltzmann Method, in order to obtain both high computational efficiency and precise dynamics. We succeed to reproduce the flow dynamics of polymers under shear. Moreover, the model is extended to include long-range interactions of functional groups. In low dielectric constant medium such as lubricant oils, the functional groups interact as ionic groups in high dielectric constant medium such as waters. The specific results shows that the colloidal science in oils have many problems to be solved.

Cavallo's multiplier for in situ generation of high voltage

A classic electrostatic induction machine, Cavallo's multiplier, is suggested for in situ production of very high voltage in cryogenic environments. The device is suitable for generating a large electrostatic field under conditions of very small load current. Operation of the Cavallo multiplier is analyzed, with quantitative description in terms of mutual capacitances between electrodes in the system. A demonstration apparatus was constructed, and measured voltages are compared to predictions based on measured capacitances in the system. The simplicity of the Cavallo multiplier makes it amenable to electrostatic analysis using finite element software, and electrode shapes can be optimized to take advantage of a high dielectric strength medium such as liquid helium. A design study is presented for a Cavallo multiplier in a large-scale, cryogenic experiment to measure the neutron electric dipole moment.

A Hybrid Quantum-Classical Model of Electrostatics in Multiply Charged Quantum Dots

We present a general model for describing the properties of excess electrons in multiply charged quantum dots (QDs). Key factors governing Fermi-level energies and electron density distributions are investigated by treating carrier densities, charge compensation, and various material and dielectric medium properties as independently tunable parameters. Electronic interactions are described using a mean-field electrostatic potential calculable through Gauss's Law by treating the quantum dot as a sphere of uniform charge density. This classical approximation modifies the Particle in a Sphere'' Schrodinger equation for a square well potential and reproduces the broken degeneracy and Fermi-level energies expected from experiment and first-principles methods. Several important implications emerge from this model: (i) Excess electron density drifts substantially towards the QD surfaces with high electron densities and large radii, and when solvated by a high dielectric medium. (ii) The maximum density of condu...

Dihedral Angle-Based Sampling of Natural Product Polyketide Conformations: Application to Permeability Prediction.

Macrocycles pose challenges for computer-aided drug design due to their conformational complexity. One fundamental challenge is identifying all low-energy conformations of the macrocyclic ring, which is important for modeling target binding, passive membrane permeation, and other conformation-dependent properties. Macrocyclic polyketides are medically and biologically important natural products characterized by structural and functional diversity. Advances in synthetic biology and semisynthetic methods may enable creation of an even more diverse set of non-natural product polyketides for drug discovery and other applications. However, the conformational sampling of these flexible compounds remains demanding. We developed and optimized a dihedral angle-based macrocycle conformational sampling method for macrocycles of arbitrary structure, and here we apply it to diverse polyketide natural products. First, we evaluated its performance using a data set of 37 polyketides with available crystal structures, with 9-22 rotatable bonds in the macrocyclic ring. Our optimized protocol was able to reproduce the crystal structure of polyketides' aglycone backbone within 0.50 Å RMSD for 31 out of 37 polyketides. Consistent with prior structural studies, our analysis suggests that polyketides tend to have multiple distinct low-energy structures, including the bioactive (target-bound) conformation as well as others of unknown significance. For this reason, we also introduce a strategy to improve both efficiency and accuracy of the conformational search by utilizing torsional restraints derived from NMR vicinal proton couplings to restrict the conformational search. Finally, as a first application of the method, we made blinded predictions of the passive membrane permeability of a diverse set of polyketides, based on their predicted structures in low- and high-dielectric media.

Modifications of spheroid plasmonic particle geometry for enhancement of ultrathin semiconductor infrared detectors

We consider the enhancement of the specific detectivity of semiconductor infrared detectors utilizing a redshifted plasmonic light concentrator. To this purpose submicrometer-sized doped transparent conductive oxide particles with different shapes were used, embedded within high dielectric permittivity medium. The whole structure was topped with a graded antireflective layer. Localized surface plasmon resonance ensures high field localization around the plasmonic particles and directly beneath them, which translates into high density of optical energy within the detector active region. We investigate the possibilities to tune the particle shape and size in order to maximize the photodetector optical energy input, i.e. to maximize the detector external quantum efficiency. We perform ab initio simulation of the optical response utilizing the finite element method, starting with spherical particles and then extending this to include spheroids and sub-micrometric plates. As an illustrative example, we analyze a mercury cadmium telluride infrared detector with an ultrathin active epitaxial active layer. An increase in external quantum efficiency is obtained for non-spherical particles compared to the spherical ones. This can be used to offset a decrease in the optical path/internal quantum efficiency. Plasmonic localization is convenient for this since optical energy density is strongly localized close to the illuminated surface, thus ensuring a large decrease of the total detector volume and therefore suppressing the generation-recombination noise levels which are proportional to the device volume. Our results show that it is possible by this approach to realize an uncooled semiconductor detector for mid-wavelength infrared range with its specific detectivity strongly increased compared to the conventional devices.

Protonation and Deprotonation Reaction of Aspartic Acid Side Chain Modulated by the Surrounding Dielectric Medium - AB Initio Quantum Chemical Studies on Aspartic Acid in Sixteen Different Solvents and Two Protein Structures

Side chain of aspartic acid constitutes of carboxylate group, pKa equals to 3.7, in aqueous solution. However, large pKa shifts are often observed in protein structures. Several aspartic acid side chains are found in protonated form in protein NMR structures, for example, Asp26 in human thioredoxin, Asp96 in bacteriorhodopsin etc. Local micro-environment plays a crucial role in pKa shift of this amino acid side chain. Question asked in this study - how variation in the local dielectric medium influence protonation of aspartic acid side chain? To answer this question, we have performed Density Functional Theory (DFT) and Möller-Plesset second order perturbation theory (MP2) calculations on aspartic acid side chain in 16 different implicit solvents with varying dielectric constants. These calculations show that bond order of carboxylic-OH group decreases steeply in low dielectric range (ε between 1 to 9). Change in bond order within high dielectric range (ε > 20) is small. This calculation suggests that carboxylic-OH bond order in aspartic acid side chain should be high in protein hydrophobic region (low dielectric medium) compared to protein hydrophilic region (high dielectric medium). This fact was verified from bond order, electron densities on aspartic acids in two different proteins, ASP96 for bacteriorhodopsin and ASP52 for hen-egg-white-lysozyme, using hybrid quantum mechanics/molecular mechanics (QM/MM) approaches. The aspartic acids and the surrounding hydrophobic region was treated quantum chemically and the remaining part of the proteins were treated with classical mechanics. The details of the QM/MM analyses will be discussed.

Generalized Born and Explicit Solvent Models for Free Energy Calculations in Organic Solvents: Cyclodextrin Dimerization.

Evaluation of solvation (binding) free energies with implicit solvent models in different dielectric environments for biological simulations as well as high throughput ligand screening remain challenging endeavors. In order to address how well implicit solvent models approximate explicit ones we examined four generalized Born models (GB(Still), GB(HCT), GB(OBC)I, and GB(OBC)II) for determining the dimerization free energy (ΔG(0)) of β-cyclodextrin monomers in 17 implicit solvents with dielectric constants (D) ranging from 5 to 80 and compared the results to previous free energy calculations with explicit solvents ( Zhang et al. J. Phys. Chem. B 2012 , 116 , 12684 - 12693 ). The comparison indicates that neglecting the environmental dependence of Born radii appears acceptable for such calculations involving cyclodextrin and that the GB(Still) and GB(OBC)I models yield a reasonable estimation of ΔG(0), although the details of binding are quite different from explicit solvents. Large discrepancies between implicit and explicit solvent models occur in high-dielectric media with strong hydrogen bond (HB) interruption properties. ΔG(0) with the GB models is shown to correlate strongly to 2(D-1)/(2D+1) (R(2) ∼ 0.90) in line with the Onsager reaction field ( Onsager J. Am. Chem. Soc. 1936 , 58 , 1486 - 1493 ) but to be very sensitive to D (D < 10) as well. Both high-dielectric environments where hydrogen bonds are of interest and low-dielectric media such as protein binding pockets and membrane interiors therefore need to be considered with caution in GB-based calculations. Finally, a literature analysis of Gibbs energy of solvation of small molecules in organic liquids shows that the Onsager relation does not hold for real molecules since the correlation between ΔG(0) and 2(D-1)/(2D+1) is low for most solutes. Interestingly, explicit solvent calculations of the solvation free energy ( Zhang et al. J. Chem. Inf. Model . 2015 , 55 , 1192 - 1201 ) reproduce the weak experimental correlations with 2(D-1)/(2D+1) very well.

Toward a Lithium-‘air’ Battery: The Effect of CO2 on the Chemistry of a Lithium-Oxygen Cell

Lithium-oxygen chemistry offers the highest energy density for a rechargeable system; such a system is known as a “lithium-air battery”. Most studies of lithium-air batteries have focused on demonstrating battery operations in an environment of pure oxygen; such a battery should technically be described as a “lithium-dioxygen (O2) battery”. Consequently, the next step for the lithium-“air” battery is to understand how the reaction chemistry is affected by the constituents of ambient air. Among the components of air, CO2 is of particular interest because its solubility in organic solvents is about fifty times higher than that of O2, and it can react actively with O2 - ·, which is the key intermediate species in Li-O2 battery reactions. In this work, we investigated the reaction mechanisms in the Li-O2/CO2 cell under various electrolyte conditions using quantum mechanical simulations combined with experimental verification. Our most important finding is that the subtle balance among various reaction pathways influencing the potential energy surfaces can be modified by the electrolyte solvation effect. Thus, a low dielectric electrolyte tends to primarily form Li2O2, while a high dielectric electrolyte is effective in electrochemically activating CO2, yielding only Li2CO3. Most surprisingly, we further discovered that a high dielectric medium such as DMSO can result in the reversible reaction of Li2CO3 within a Li-air cell (contrary to conventional belief) over multiple cycles. We believe that the current mechanistic understanding of the chemistry of CO2 in a Li-air cell and the interplay of CO2 with electrolyte solvation will provide an important guideline for developing Li-air batteries. Furthermore, the newly discovered possibility for a rechargeable Li-O2/CO2 battery based on Li2CO3 formation chemistry may have merits in enhancing cyclability by minimizing side reactions.