Measurement of Transport Number of Lithium in Glycerol Assisted by Fourier Transform Spectroscopy Analysis: Progress towards Elaboration of Optimal Electrolyte of Friendly Environmental Battery

Up to now, a great deal of research investigations on lithium ion conductors has been carried out, because they are potentially utilized in the solid electrolytes of the batteries and the electrochemical devices. However, in order to elaborate new ecological batteries of lithium, it becomes primordial to study and understand the properties of transport of the lithium electrolytes using eco-friendly solvents, with view perhaps to find out the best electrolyte for such devices. In fact, the electromotive forces (EMFs) of lithium chloride electrolyte in the hydrogen-bonded solvents glycerol, were measured using the concentration cells (CCs) 0.005/0.05 and 0.05/0.5. Then the transport numbers of the lithium-ion were deduced by means of the Nernst equation in combination with the Debye-Huckel limiting law. Whilst the activation energy values were calculated from the parameters of the fitting of the transference number data to the empirical power law, yielding a regression coefficient of 95.9% for the most concentrated concentration cell. The structure and interactions in the lithium electrolyte solution were studied by vibrational Infra-Red spectroscopy. The experimental data were discussed and compared to those obtained previously, using impedance spectroscopy of glass-forming glycerolate lithium electrolytes for the same purpose. Despite the enormous difference between their viscosities; glycerol shows similar activation energy (i.e. 31.40 kJ.mol–1) with water (i.e. 31.73 kJ.mol–1), in particular at very low concentration, confirming both solvents being hydrogen-bonded. Besides, this study suggests the utilization of the glycerol-lithium ion electrolyte for future conception of ecological lithium-ion battery, rather than those using ion electrolyte polymer currently on the market. Similarly to relaxation and conductivity, the transport number data suggests that the diffusion of conformational states is also monitoring the overall lithium ion transport mechanism.

Ion Coordination and Transport in Magnesium Polymer Electrolytes Based on Polyester-co-Polycarbonate

Magnesium-ion-conducting solid polymer electrolytes have been studied for rechargeable Mg metal batteries, one of the beyond-Li-ion systems. In this paper, magnesium polymer electrolytes with magnesium bis(trifluoromethane)sulfonimide (Mg(TFSI)2) salt in poly(ε-caprolactone-co-trimethylene carbonate) (PCL-PTMC) were investigated and compared with the poly(ethylene oxide) (PEO) analogs. Both thermal properties and vibrational spectroscopy indicated that the total ion conduction in the PEO electrolytes was dominated by the anion conduction due to strong polymer coordination with fully dissociated Mg2+. On the other hand, in PCL-PTMC electrolytes, there is relatively weaker polymer–cation coordination and increased anion–cation coordination. Sporadic Mg- and F-rich particles were observed on the Cu electrodes after polarization tests in Cu|Mg cells with PCL-PTMC electrolyte, suggesting that Mg was conducted in the ion complex form (MgxTFSIy) to the copper working electrode to be reduced which resulted in anion decomposition. However, the Mg metal deposition/stripping was not favorable with either Mg(TFSI)2 in PCL-PTMC or Mg(TFSI)2 in PEO, which inhibited quantitative analysis of magnesium conduction. A remaining challenge is thus to accurately assess transport numbers in these systems.

Putting Together the Puzzle of Ion Transfer in Single-Digit Carbon Nanotubes: Ab Initio Meets Mean-Field

Nature employs channel proteins to selectively pass water across cell membranes, which inspires search for bio-mimetic analogues. Carbon nanotube porins (CNTPs) are intriguing mimics of water channels, yet ion transport in CNTPs still poses questions. As alternative to continuum models, here we present a molecular mean-field model, computing ab initio all required thermodynamic quantities for KCl salt and H+ and OH- ions present in water. Starting from water transfer, the model considers transfer of free ions, along with ion-pair formation to address ion-ion interactions. High affinity to hydroxide, suggested by experiments and making it dominant charge carrier in CNTP, is revealed as an exceptionally favorable transfer of KOH pairs. Nevertheless, free ions, coexisting with less mobile ion-pairs, apparently control ion transport. The model explains well the observed effects of salt concentration and pH on conductivity, transport numbers, anion permeation and its activation energies, and current rectification. The proposed approach is extendable to other sub-nanochannels and help design novel osmotic materials and devices.

Use of the Microheterogeneous Model to Assess the Applicability of Ion-Exchange Membranes in the Process of Generating Electricity from a Concentration Gradient

The paper shows the possibility of using a microheterogeneous model to estimate the transport numbers of counterions through ion-exchange membranes. It is possible to calculate the open-circuit potential and power density of the reverse electrodialyzer using the data obtained. Eight samples of heterogeneous ion-exchange membranes were studied, two samples for each of the following types of membranes: Ralex CM, Ralex AMH, MK-40, and MA-41. Samples in each pair differed in the year of production and storage conditions. In the work, these samples were named “batch 1” and “batch 2”. According to the microheterogeneous model, to calculate the transport numbers of counterions, it is necessary to use the concentration dependence of the electrical conductivity and diffusion permeability. The electrolyte used was a sodium chloride solution with a concentration range corresponding to the conditional composition of river water and the salinity of the Black Sea. During the research, it was found that samples of Ralex membranes of different batches have similar characteristics over the entire range of investigated concentrations. The calculated values of the transfer numbers for membranes of different batches differ insignificantly: ±0.01 for Ralex AMH in 1 M NaCl. For MK-40 and MA-41 membranes, a significant scatter of characteristics was found, especially in concentrated solutions. As a result, in 1 M NaCl, the transport numbers differ by ±0.05 for MK-40 and ±0.1 for MA-41. The value of the open circuit potential for the Ralex membrane pair showed that the experimental values of the potential are slightly lower than the theoretical ones. At the same time, the maximum calculated power density is higher than the experimental values. The maximum power density achieved in the experiment on reverse electrodialysis was 0.22 W/m2, which is in good agreement with the known literature data for heterogeneous membranes. The discrepancy between the experimental and theoretical data may be the difference in the characteristics of the membranes used in the reverse electrodialysis process from the tested samples and does not consider the shadow effect of the spacer in the channels of the electrodialyzer.

Investigating the Proton and Ion Transfer Properties of Supported Ionic Liquid Membranes Prepared for Bioelectrochemical Applications Using Hydrophobic Imidazolium-Type Ionic Liquids

Hydrophobic ionic liquids (IL) may offer a special electrolyte in the form of supported ionic liquid membranes (SILM) for microbial fuel cells (MFC) due to their advantageous mass transfer characteristics. In this work, the proton and ion transfer properties of SILMs made with IL containing imidazolium cation and [PF6]− and [NTf2]− anions were studied and compared to Nafion. It resulted that both ILs show better proton mass transfer and diffusion coefficient than Nafion. The data implied the presence of water microclusters permeating through [hmim][PF6]-SILM to assist the proton transfer. This mechanism could not be assumed in the case of [NTf2]− containing IL. Ion transport numbers of K+, Na+, and H+ showed that the IL with [PF6]− anion could be beneficial in terms of reducing ion transfer losses in MFCs. Moreover, the conductivity of [bmim][PF6]-SILM at low electrolyte concentration (such as in MFCs) was comparable to Nafion.

Using a microheterogeneous model to assess the applicability of ion-exchange membranes in the process of reverse electrodialysis

This paper shows the possibility of using a microheterogeneous model to describe the properties of ion-exchange membranes and calculate the characteristics of a reverse electrodialyzer from the data obtained. We studied the properties of eight samples of heterogeneous cation exchange membranes (two samples of each type of membrane). The samples differed in the year of issue and storage conditions. It is shown that for heterogeneous ion-exchange membranes MK-40 and MA-41, the samples' properties can differ significantly. The counterions transport numbers calculated within the framework of the microheterogeneous model for Ralex membranes differ insignificantly. The counterion transport number in 1 mol/L sodium chloride solution is 0.96 for Ralex CM and 0.98 ± 0.01 for Ralex AMH. For the MK-40 membrane, the transport number in the same solution is 0.94 ± 0.04, and for the MA-41 membrane, it is 0.85 ± 0.1. The possibility of calculating the transport numbers and predicting the open-circuit voltage based on simple physicochemical measurements allows selecting the best membrane pairs for the reverse electrodialysis process. Comparison of the open-circuit potential value calculated using the obtained transfer numbers with experimental data showed that in the case of using Ralex membranes, the difference between the experimental and calculated values is 2%. The calculated value of the open circuit potential was 0.19 V/membrane pair or 1.69 V for the investigated reverse electrodialyzer with nine pair chambers.

Effect of TiO2 Nano-filler on Electrical Properties of Na+ Ion Conducting PEO/PVDF Based Blended Polymer Electrolyte

Nanocomposite Polymer Electrolyte (NCPE) films based on a blend of two polymers poly (ethylene oxide) (PEO) and poly (vinylidene fluoride) (PVDF) complexed with sodium perchlorate (NaClO4) salt and Nano-filler Titanium dioxide (TiO2) (i.e., (80wt%PEO/20wt%PVDF) + 7.5wt%NaClO4+ xwt%TiO2 where x = 3, 6, 9, 12, 15, and 18) were prepared and characterized as potential candidates for battery applications. Electrochemical Impedance Spectroscopy (EIS) has been employed between the frequencies 10 Hz and 4 MHz to investigate electrical, dielectric and electric modulus properties of the prepared NCPE films. Effect of TiO2 Nano-filler concentration on the structural, ionic conductivity, and dielectric relaxation has been studied. The AC conductivity of the NCPE films at high frequencies obeys Jonscher’s power law. The values of DC ionic conductivity calculated by fitting the AC conductivity spectra to the best fit of Joncher’s power law are consistent with the values of DC ionic conductivity calculated from the bulk resistance (Rb) of the NCPE films. The ionic conductivity that depends on temperature follows the Arrhenius rule between the temperatures 298 K and 328 K. The maximum ionic conductivity at ambient temperature 8.75x10-5 S/cm was obtained for (80wt%PEO/20wt%PVDF) +7.5wt%NaClO4 +15wt%TiO2 NCPE film and it is attributed to the decrease in crystallinity. Using Wagner’s polarization technique ionic transport numbers of various NCPE films were measured.