Non-aqueous Systems Research Articles

“Wine-Dark Sea” in an Organic Flow Battery: Storing Negative Charge in 2,1,3-Benzothiadiazole Radicals Leads to Improved Cyclability

Redox-active organic materials (ROMs) have shown great promise for redox flow battery applications but generally encounter limited cycling efficiency and stability at relevant redox material concentrations in nonaqueous systems. Here we report a new heterocyclic organic anolyte molecule, 2,1,3-benzothiadiazole, that has high solubility, a low redox potential, and fast electrochemical kinetics. Coupling it with a benchmark catholyte ROM, the nonaqueous organic flow battery demonstrated significant improvement in cyclable redox material concentrations and cell efficiencies compared to the state-of-the-art nonaqueous systems. Especially, this system produced exceeding cyclability with relatively stable efficiencies and capacities at high ROM concentrations (>0.5 M), which is ascribed to the highly delocalized charge densities in the radical anions of 2,1,3-benzothiadiazole, leading to good chemical stability. This material development represents significant progress toward promising next-generation energy st...

Investigation of Ionic Conductivity, Uptake and Cation Diffusion of Perfluorsulfonate and Sulfonated Block Copolymer Ion Exchange Membrane in Non-Aqueous Solvents

The characterization of perfluorsulfonate and sulfonated block copolymer ion exchange membranes is well established in aqueous systems. While many of these membranes have been proved to have favorable conductivity and stability in multiple applications(1,2), similar studies are hardly found for membranes in non-aqueous systems. Although some characterization results on non-aqueous system have been published(3), a complete understanding how sulfonated ion exchange membranes behave in organic solvents is lacking. The largest range of existing methods is mostly dedicated to probing aqueous systems. In light of emerging applications, especially in nonaqueous redox flow batteries (NARFBs), it is certainly desirable to combine various techniques beyond simply conductivity in hope of elucidating some of the membrane properties in non-aqueous system. A series of protocols is being developed to characterize some fundamental membrane properties. A four-point cell conductivity configuration was adopted to minimize artifacts (4). Swelling behavior was studied to complement conductivity data. In Figure 1, while the 3Mion-825EW membranes in TEA+ form overall showed higher conductivity than the Li+ form membranes. Acetonitrile soaked-TEA form membranes exhibited a 9-fold boost. This is consistent with relatively high performance of NARFBs using this electrolyte. To reveal fundamental aspects of this performance, other means of characterization are certainly necessary to look into cation/membrane/solvent matches. Fourier transform infrared spectroscopy (FTIR) was utilized to examine membranes exchanged with different cations (li+, Na+, TEA+ ,etc) so the interaction between the cation and membrane, as well as between the solvent and the membrane can be better understood. Measuring the relaxation time (T1) of cations and solvents by NMR has been an effective way to unravel the local diffusion kinetics for cation exchange membranes(5). Cation pulsed gradient diffusion experiments by NMR were carried out to further clarify the long-range transport. These data will help us explicate the correlation between the cation behavior/vibrational bonding and macroscopic properties. On top of indicating good cation/membrane/solvent matches, a more complete and precise understanding of membrane behavior in non-aqueous system is the goal of the study. The behavior of several different membrane types will be discussed. Acknowledgement We gratefully acknowledge the support of this work by the U.S. Department of Energy, Office of Electricity Delivery and Energy Reliability (Dr. Imre Gyuk). We also thank 3M for providing membranes.

(Invited) An Activity Model for Swelling of Nafion® in Varied Solvents

Nafion is used ubiquitously in aqueous electrochemical systems and commonly in nonaqueous systems. Nafion solvation varies with solvent and cation. Its concomitant swelling complicates Nafion application in various electrochemical technologies. For direct reformation PEM fuel cells that operated with solvents of alcohols and aqueous alcohols, crossover of alcohols through Nafion to the cathode degrades fuel cell performance. The cation in Nafion impacts methanol permeability where permeability ranges over three orders of magnitude for various cations, as found by Kunz and coworkers [1,2]. Aquated, Li⁺ exchanged Nafion placed in organic solvents changes level of solvation; across almost 30 solvents, swelling mapped as change in volume over aquated volume, ΔV/V ranged from 40 to 730 % [3]. Properties of Nafion have been variously reviewed, with a recent review focused on aqueous systems and change in properties with cation [4]. Recent modeling [5] of cation impact on properties of Nafion in water has developed from activity and electrochemical potential models. Here, extension of the model to nonaqueous solvents for cation exchanged Nafion is considered. Classical theories of activity evolved from Debye Hückel and Extended Debye Hückel (EDH) models where the models are applicable for ionic strength I≲0.01 M and ≲0.1 M, respectively. Activity for species i is defined as ai = γi[i] where γi is the activity coefficient and [i] is the concentration. The ionic strength in the hydrated domains of Nafion is about 10 M [4]. In further development of activity in high ionic strength, Stokes and Robinson [6] divided the solvent molecules into free and bound waters. The free waters act as solvent but bound waters are removed from the bulk solvent that dissolves the solute. The Stokes Robinson model describes the activity coefficient γSR,i for a solute ion relative to the activity coefficient for the ion according to EDH, γEDH,i. γSR,i/γEDH,i =aw -n/v [1 - 0.018 (n-v) c*]-1 where n is the number of waters bound to ion i, v is the number of ions formed when i dissolves (e.g., for NaCl, v=2), and c* is concentration of i. Because the number of free waters in high ionic strength is reduces, the activity of solvent water, aw< 1. The value 0.018 embeds properties of molecular weight and density for water. This has been used to model various properties of Nafion in an aqueous environment [5]. The Stokes Robinson model for Nafion will be adapted to model swelling of Nafion in various solvents, based on the data set in reference [3]. Preliminary results for 29 solvents yield a monotonic fit of ΔV/V with γSR,Li/γEDH,Li and a linear fit of ΔV/V with [γSR,Li/γEDH,Li]-1. A effective activity model based on the Stokes Robinson model is anticipated for various solvents. With an activity model, properties of Nafion in different solvents can be tailored for specific applications. ---

Stable Organic Redox Flow Batteries in Nonaqueous Electrolytes

Redox flow battery is a promising stationary energy storage technology, which is ascribed to the separation of energy and power leading to excellent design flexibility and scalability. To overcome the limitation of narrow electrochemical window of traditional aqueous flow batteries, considerable attention has been paid to develop nonaqueous flow systems with the hope to increase the energy density. However, the reported nonaqueous flow batteries are limited by low energy density, low rate performance, and more critically, poor cyclability. Here we report our efforts to explore the mechanisms of capacity fading and to improve the cycling stability of nonaqueous flow batteries based on organic redox-active materials.1-3 Promising organic redox candidates have been identified and structurally tailored to increase their solubilities, redox activities, and chemical stability. A rational molecular design protocol has been proposed and validated for developing stable organic flow batteries. Electrolyte engineering is also found to play a role in tuning the electrochemical performance and stability of nonaqueous flow batteries. References (1) X. Wei, W. Xu, J. Huang, L. Zhang, E. Walter, C. Lawrence, M. Vijayakumar, W. A. Henderson, T. Liu, L. Cosimbescu, B. Li, V. Sprenkle, W. Wang, Angew. Chem. Int. Ed. 2015, 54, 8684. (2) X. Wei,* W. Duan, J. Huang, L. Zhang, B. Li, D. Reed, V. Sprenkle, W. Xu, W. Wang, ACS Energy Lett. 2016, 1, 705. (3) W. Duan, R. S. Vemuri, J. D. Milshtein, S. Laramie, R. D. Dmello, J. Huang, L. Zhang, D. Hu, M. Vijayakumar, W. Wang, J. Liu, R. M. Darling, L. Thompson, K. Smith, J. S. Moore, F. R. Brushett, X. Wei, J. Mater. Chem. A, 2016, 4, 5448. Figure 1. The cycling performance of a nonaqueous organic flow battery, showing excellent cycling stability for 50 cycles. The organic redox-active materials are shown.2 Figure 1

Exploring Rate Capabilities of Symmetric Nonaqueous Redox Flow Batteries

After decades of research, widespread implementation of redox flow batteries (RFBs) for grid electricity storage has only recently begun to appear feasible. With MWh-level installations in the U.S. and GWh-level installations planned in China [1], the aqueous vanadium RFB chemistry appears to be the market leader. These projects offer levelized cost of capacity lower than the large Li-ion storage systems offered by suppliers like Tesla. A recent US study, which used the state of Michigan’s electrical grid as a test case, found that RFBs reduced emissions per kWh in all scenarios, but also found that RFBs were only economically preferable to wind curtailment at curtailment levels above 66% [2]. So there remains a need to find alternative, less costly energy storage strategies to better compete with other carbon-intensity improvement strategies that are available to utilities. Symmetric RFBs offer a step-change reduction in reactor cost because their use of identical solutions in the discharged posolyte and negolyte mitigates the need for expensive ion-exchange-membrane separators. Many symmetric RFB chemistries exist: redox-active organometallic chemistries such as V(acac)3 ­[3], or redox-active organic chemistries such as polycyclic aromatic hydrocarbons [4]. These RFB chemistries operate at voltages that split water, requiring nonaqueous environments. Nonaqueous RFBs are often rejected out of hand, based on their expected inability to provide reasonable power. Such an expectation is based on a qualitative argument that nonaqueous solutions tend to have low conductivites, and consequently cannot support high-current operation. However, ion-exchange membranes in aqueous solutions also tend to have similarly low conductivities. Being freed from the need for costly, resistive ion-exchange membranes, symmetric chemistries can employ inexpensive porous polyolefin separators, which we will show can permit rate performance comparable to aqueous vanadium RFBs. Results were collected from a bespoke system involving a 6.25 cm2 flow-through reactor and 100 mL active-liquid storage vessels: the positive and negative flow-through regions contained carbon felt at 6% compression to fit the 3 mm depth. Flow cell designs of these nonaqueous systems are non-trivial since many of the materials used in these nonaqueous chemistries are incompatible with materials used for aqueous systems. We will discuss some design criteria and lessons learned in the fabrication of these nonaqueous flow cells. Figure 1 shows 20 cycles of a symmetric V(acac)3 cell operating at 20 mAcm–2 in a cell with a porous polyolefin separator. The voltage cutoff was not triggered during the charging procedure, allowing the charging cycles to achieve the full programmed capacity. The coulombic efficiency, voltage efficiency, and energy efficiency quickly stabilize to 83%, 87%, and 72%, respectively. Informed by similar data across a range of charge/discharge currents and flow rates, we will report more generally on the performance of nonaqueous symmetric RFB chemistries. [1] Unienergy Technologies. www.uetechnologies.com. Accessed Dec. 2016. [2] M. Arbabzadeh, et al. Appl. Energy 2015, 146, 397. [3] Q. Liu et al. Electrochem. Comm. 11 (2009): 2312. [4] J. Saraidaridis et al. ECS Meeting on Electrochemical Energy and Storage s. (2015): 685. Figure 1: 0.1 M V(acac)3/0.5 M TEABF4 in acetonitrile, 20 mAcm-2, polypropylene separator, 50% SOC charging cycles after 1st charge to 75%, 50% SOC 1st discharge and to 1 V cutoff on subsequent cycles, Argon atmosphere with <1ppm O2, H2O Figure 1

Carbon Dioxide Capture by Diethylenetriamine Hydrobromide in Nonaqueous Systems and Phase-Change Formation

Diethylenetriamine hydrobromide ([DETAH]Br) was used for capturing CO2 in polyethylene glycol 200 (PEG200) solution, in which phase change was observed. PEG200 could not only act as a cosolvent but also be involved in CO2 absorption, contributing to biphasic separation and increased CO2 capacity. The potential applications of the mixtures would take advantage of high CO2 capacity (1.184 mol/mol [DETAH]Br), and also less energy consumed when considering the mild regeneration condition and low specific heat of PEG200. This system could be recycled at least for five continuous absorption–desorption cycles without significant loss of CO2 capturing and releasing capability. Spectroscopic analysis revealed a O–H···:N type of H-bonding, and the stabilizing effects of bromide ion would play important roles in stabilizing the system and preventing the biphasic separation by overcoming the electrostatic attractions in the early stage of CO2 absorption. It is estimated that such a simple and inexpensive solution pro...

Pyrrole-based poly(ionic liquids) as efficient stabilizers for formation of hollow multi-walled carbon nanotubes particles

Poly(ionic liquid) (PIL) derivatives with pyrrole intrinsically conducting polymer (ICP) backbones were synthesized and utilized as novel dispersants of multi-walled carbon nanotubes (MWCNTs) in various aqueous and non-aqueous systems, including polar and nonpolar solvents. This is due to the highly tunable nature of the PIL, in which the PILs of varying polarity with the same pyrrole-based polycation can be synthesized. The dispersions are exceedingly stable over many months, and with the addition of hexane, Pickering (solid-stabilized) emulsions with the PIL-stabilized MWCNTs at the droplet interfaces were formed. Depending on the hydrophobicity of the PIL, hexane-in-water and hexane-in-acetonitrile emulsions were formed, the latter marking the first non-aqueous CNT-stabilized emulsions, further advancing the processability of CNTs. The PIL-stabilized CNT Pickering emulsion droplets generated hollow conductive particles by subsequent drying of the emulsions. With emulsion templating, the hollow shells could be used as a payload carrier, depending on the solubility of the payload in the droplet phase of the emulsion. This was demonstrated with silicon nanoparticles, which have limited dispersibility in aqueous environments, but great scientific interest due to their potential electrochemical applications. Overall, this work explored a new class of efficient PIL-ICP hybrid stabilizers with tunable hydrophobicity, with hollow particle formation capability.

In situ SERS and SHINERS study of electrochemical hydrogenation of p-ethynylaniline in nonaqueous solvents

Surface-enhanced Raman spectroscopy (SERS) studies of electrode/solution interfaces are important for understanding electrochemical processes. However, revealing the nature of reactions at well-defined single crystal electrode surfaces, which are SERS-inactive, remains challenging. In this work, shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) was used for the first time to study electrochemical adsorption and hydrogenation reactions at single crystal surfaces in nonaqueous solvents. A roughened Au surface was also studied for comparison. The experimental results show that the hydrogenation of adsorbed p-ethynylaniline (PEAN) on roughened Au electrode surfaces occurred at very negative potentials in methanol because of the catalytic effect of surface plasmon resonance (SPR). However, because “hot electrons” were blocked by the silica shell of Au@SiO2 nanoparticles and aprotic acetonitrile was an ineffective hydrogen source, surface reactions at Au(111) were inhibited in the systems studied. Density functional theory (DFT) calculations revealed that the PEAN triple bond opened, allowing adsorption in a flat configuration on the Au(111) surface via two carbon atoms. This work provides an advanced understanding of electrochemical interfacial processes at single crystal surfaces in nonaqueous systems.

High Performance Redox Flow Batteries: An Analysis of the Upper Performance Limits of Flow Batteries Using Non-aqueous Solvents

Redox Flow Batteries (RFBs) are a promising technology for grid-scale electrochemical energy storage. In this work, we use a recently achieved high-performance flow battery performance curve as a basis to assess the maximum achievable performance of a RFB employing non-aqueous solutions as active materials. First we show high performance in a vanadium redox flow battery (VRFB), specifically a limiting situation in which the cell losses are ohmic in nature and derive from electrolyte conductance. Based on that case, we analyze the analogous limiting behavior of non-aqueous (NA) systems using a series of calculations assuming similar ohmic losses, scaled by the relative electrolyte resistances, with a higher voltage redox couple assumed for the NA battery. The results indicate that the NA battery performance is limited by the low electrolyte conductivity to a fraction of the performance of the VRFB. Given the narrow window in which the NARFB offers advantages, even for the most generous limiting assumptions related to performance while ignoring the numerous other disadvantageous aspects of these systems, we conclude that this technology is unlikely under present circumstances to provide practical large-scale energy storage solutions.

Cobalt(II) complexes with azole-pyridine type ligands for non-aqueous redox-flow batteries: Tunable electrochemistry via structural modification

Abstract A single species redox flow battery employing a new class of cobalt(II) complexes with ‘tunable’ tridentate azole-pyridine type ligands is reported. Four structures were synthesised and their electrochemical, physical and battery characteristics were investigated as a function of successive substitution of the ligand terminal pyridyl donors. The Co(II/I) and Co(III/II) couples are stable and quasi-reversible on gold and glassy carbon electrodes, however redox potentials are tunable allowing the cobalt potential difference to be preferentially increased from 1.07 to 1.91 V via pyridine substitution with weaker σ-donating/π-accepting 3,5-dimethylpyrazole groups. The charge-discharge properties of the system were evaluated using an H-type glass cell and graphite rod electrodes. The complexes delivered high Coulombic efficiencies of 89.7–99.8% and very good voltaic efficiencies of 70.3–81.0%. Consequently, energy efficiencies are high at 63.1–80.8%, marking an improvement on other similar non-aqueous systems. Modification of the ligands also improved solubility from 0.18 M to 0.50 M via pyridyl substitution with 3,5-dimethylpyrazole, though the low solubility of the complexes limits the overall energy capacity to between 2.58 and 12.80 W h L −1 . Preliminary flow cell studies in a prototype flow cell are also demonstrated.

Solid-State Ionic Diodes Demonstrated in Conical Nanopores

Ionic transport at the nanoscale features phenomena that are not observed in larger systems. Nonlinear current–voltage curves characteristic of ionic diodes as well as ion selectivity are examples of effects observed at the nanoscale. Many man-made nanopore systems are inspired by biological channels in a cell membrane, thus measurements are often performed in aqueous solutions. Consequently, much less is known about ionic transport in nonaqueous systems, especially in solid-state electrolytes. Here we show ionic transport through single pores filled with gel electrolyte of poly(methyl methacrylate) (PMMA) doped with LiClO4 in propylene carbonate. The system has no liquid interface and the ionic transport occurs through the porous gel structure. We demonstrate that a conically shaped nanopore filled with the gel rectifies the current and works as a solid-state ionic diode.

Exploring the Ni redox activity in polyanionic compounds as conceivable high potential cathodes for Na rechargeable batteries

Although nickel-based polyanionic compounds are expected to exhibit a high operating voltage for batteries based on the Ni2+/3+ redox couple activity, some rare experimental studies on the electrochemical performance of these materials are reported, resulting from the poor kinetics of the bulk materials in both Li and Na nonaqueous systems. Herein, the electrochemical activity of the Ni2+/3+ redox couple in the mixed-polyanionic framework Na4Ni3(PO4)2(P2O7) is reported for the first time. This novel material exhibits a remarkably high operating voltage when cycled in sodium cells in both carbonate- and ionic liquid-based electrolytes. The application of a carbon coating and the use of an ionic liquid-based electrolyte enable the reversible sodium ion (de-)insertion in the host structure accompanied by the redox activity of Ni2+/3+ at operating voltages as high as 4.8 V vs Na/Na+. These results present the realization of Ni-based mixed polyanionic compounds with improved electrochemical activity and pave the way for the discovery of new Na-based high potential cathode materials.

Whole-Cell Biocatalytic Synthesis of Cinnamyl Acetate with a Novel Esterase from the DNA Library of Acinetobacter hemolyticus

Cinnamyl acetate has a wide application in the flavor and fragrance industry because of its sweet, balsamic, and floral odor. Up to now, lipases have been mainly used in enzyme-mediated synthesis of cinnamyl acetate, whereas esterases are used in only a few cases. Moreover, the use of purified enzymes is often a disadvantage, which leads to increases of the production costs. In this paper, a genomic DNA library of Acinetobacter hemolyticus was constructed, and a novel esterase (EstK1) was identified. After expression in Escherichia coli, the whole-cell catalyst of EstK1 displayed high transesterification activity to produce cinnamyl acetate in nonaqueous systems. Furthermore, under optimal conditions (vinyl acetate as acyl donor, isooctane as solvent, molar ratio 1:4, temperature 40 °C), the conversion ratio of cinnamyl alcohol could be up to 94.1% at 1 h, and it reached an even higher level (97.1%) at 2 h.

Bulk-Type All-Solid-State Lithium-Ion Batteries: Remarkable Performances of a Carbon Nanofiber-Supported MgH2 Composite Electrode.

Magnesium hydride, MgH2, a recently developed compound for lithium-ion batteries, is considered to be a promising conversion-type negative electrode material due to its high theoretical lithium storage capacity of over 2000 mA h g-1, suitable working potential, and relatively small volume expansion. Nevertheless, it suffers from unsatisfactory cyclability, poor reversibility, and slow kinetics in conventional nonaqueous electrolyte systems, which greatly limit the practical application of MgH2. In this work, a vapor-grown carbon nanofiber was used to enhance the electrical conductivity of MgH2 using LiBH4 as the solid-state electrolyte. It shows that a reversible capacity of over 1200 mA h g-1 with an average voltage of 0.5 V (vs Li/Li+) can be obtained after 50 cycles at a current density of 1000 mA g-1. In addition, the capacity of MgH2 retains over 1100 mA h g-1 at a high current density of 8000 mA g-1, which indicates the possibility of using MgH2 as a negative electrode material for high power and high capacity lithium-ion batteries in future practical applications. Moreover, the widely studied sulfide-based solid electrolyte was also used to assemble battery cells with MgH2 electrode in the same system, and the electrochemical performance was as good as that using LiBH4 electrolyte.

Perspective—State of the Art of Rechargeable Aluminum Batteries in Non-Aqueous Systems

The main challenges to implement sustainable energy storage technologies are the utilization of earth-abundant recyclable materials, low costs, safe cell reactions and high performance, all in a single system. Aluminum batteries seem to cover these requirements. However, their practical performance is still not comparable with the state of the art high performance batteries. A key aspect to further development could be the combination of aluminum with charge storage materials like conductive polymers in non-aqueous electrolytes taking advantage of the properties of each material. This review presents the approaches and perspectives for rechargeable aluminum-based batteries as sustainable high-performance energy storage devices.

Progress and directions in low-cost redox-flow batteries for large-scale energy storage

AbstractCompared to lithium-ion batteries, redox-flow batteries have attracted widespread attention for long-duration, large-scale energy-storage applications. This review focuses on current and future directions to address one of the most significant challenges in energy storage: reducing the cost of redox-flow battery systems. A high priority is developing aqueous systems with low-cost materials and high-solubility redox chemistries. Highly water-soluble inorganic redox couples are important for developing technologies that can provide high energy densities and low-cost storage. There is also great potential to rationally design organic redox molecules and fine-tune their properties for both aqueous and non-aqueous systems. While many new concepts begin to blur the boundary between traditional batteries and redox-flow batteries, breakthroughs in identifying/developing membranes and separators and in controlling side reactions on electrode surfaces also are needed.

Towards Low Resistance Nonaqueous Redox Flow Batteries

Nonaqueous redox flow batteries (NAqRFBs) are a promising, but nascent, concept for cost-effective grid-scale energy storage. While most studies report new active molecules and proof-of-concept prototypes, few discuss cell design. The direct translation of aqueous RFB design principles to nonaqueous systems is hampered by a lack of materials-specific knowledge, especially concerning the increased viscosities and decreased conductivities associated with nonaqueous electrolytes. To guide NAqRFB reactor design, recent techno-economic analyses have established an area specific resistance (ASR) target of <5 Ω cm2. Here, we employ a state-of-the-art vanadium flow cell architecture, modified for compatibility with nonaqueous electrolytes, and a model ferrocene-based redox couple to investigate the feasibility of achieving this target ASR. We identify and minimize sources of resistive loss for various active species concentrations, electrolyte compositions, flow rates, separators, and electrode thicknesses via polarization and impedance spectroscopy, culminating in the demonstration of a cell ASR of ca. 1.7 Ω cm2. Further, we validate performance scalability using dynamically similar cells with a ten-fold difference in active areas. This work demonstrates that, with appropriate cell engineering, low resistance nonaqueous reactors can be realized, providing promise for the cost-competitiveness of future NAqRFBs.

Probing electrochemical interfaces using shell-isolated nanoparticles-enhanced Raman spectroscopy

Electrochemical solid/liquid interface earned huge interest due to its wide range of application in various fundamental research fields. Combining with electrochemical methods, shell-isolated nanoparticles-enhanced Raman spectroscopy (SHINERS) can be employed as a promising technique for better understanding of interface reaction processes. In recent times, it has received great attention by research community as it is universally applicable to many material and morphology surfaces in electrochemical and surface science fields. Based on the recent progress of EC-SHINERS, we first briefly reviewed the development of SHINERS history, and then followed with a detailed introduction of SHINERS application in various electrochemical interfaces studies, including the molecule adsorption, corrosion resistance, catalytic reactions and other applications in different fields from aqueous to non-aqueous systems.

Prediction of Electrolyte Conductivity: Results from a Generalized Molecular Model Based on Ion Solvation and a Chemical Physics Framework

Ionic conductivity is a foremost transport property that is extensively used to characterize and screen electrolyte systems. Although bulk measurements are done on the macroscopic scale, electrolytic conductivity has its foundation on molecular-scale interactions between solvent and ionic species. Correct interpretations of these molecular interactions and related quantities enable a balanced, comprehensive understanding of conductivity behavior with respect to system conditions (solvent composition, salt concentration and temperature). This work introduces a new methodology that achieves accurate predictions of electrolyte conductivity for a wide range of conditions, based on molecular, physical, and chemical terms. The formalism is universal, making it valid for aqueous and non-aqueous systems alike. The immediate application of the resultant model is candidate electrolytes for lithium-ion and sodium-ion batteries, although many other applications abound for systems that utilize liquid electrolytes. Conductivity predictions are compared to experimental data for a number of electrolytes over a wide range of conditions, demonstrating that exceptional accuracy is attained because the robust model captures multiple salient contributions to conductivity behavior. Model accuracy is well maintained over multi-solvent systems and for extended salt concentrations.

Enhancement of oxygen reduction reaction rate by addition of water to an oxidatively stable ionic liquid electrolyte for lithium-air cells

The oxygen reduction reaction in an ionic liquid (IL) consisting of N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium (DEME) cation and the bis(trifluoromethanesulfonyl)imide (TFSI) anion was investigated in the anhydrous and water saturated conditions respectively. The IL was demonstrated to be stable in the operating range of a lithium air cell in both the anhydrous and water saturated conditions. The addition of water was found to lower the overpotential for the oxygen reduction reaction by 40mV. Finally, the reaction rate constant was found to increase by an order of magnitude with the addition of water hence demonstrating the tendency of water to promote/catalyze the oxygen electrochemistry in non-aqueous systems.