Membranes and Membrane Technologies最新文献

One of the main trends in the development of metal-ion batteries concerns the transition to lithium anodes, the safe use of which is impossible without replacing liquid membranes with solid ones, primarily inorganic membranes. Lithium–niobium–chromium phosphates with calculated compositions Li_3–2xNb_xCr_2–x(PO₄)₃ (х = 0.95, 1.00, 1.05) were obtained by solid-state synthesis and characterized by XRD analysis and impedance spectroscopy. The obtained complex lithium-niobium-chromium phosphates with the NASICON structure crystallize in hexagonal modification. The unit cell parameters of crystal lattice of the synthesized materials decrease with increasing chromium content. The highest ionic conductivity and the lowest activation energy are exhibited by the material of composition Li_1.1Nb_0.95Cr_1.05(PO₄)₃ (3 × 10^–5 S/cm at 25°С), which indicates a greater mobility of lithium ions by the interstitial mechanism even in the region of its own disorderliness.

The physicochemical and transport characteristics of cast and extruded MF-4SK perfluorinated membranes modified with zirconium hydrogen phosphate in an amount of 3–10% are studied. The inorganic phase is formed directly in the membrane volume by the pore-filling method. The effect of zirconium hydrogen phosphate content on the ion-exchange capacity, water content, diffusion permeability for electrolyte solution, hydrogen gas permeability, and electrical conductivity at the limited humidity of the MF-4SK membrane, as well as the efficiency of its use in a low-temperature proton-exchange membrane fuel cell, are investigated. A nonmonotonic change in the transport characteristics depending on the dopant content is demonstrated. The lowest diffusion permeability and maximum electrical conductivity at low humidity are exhibited by the membrane containing 6% of zirconium hydrogen phosphate. It is shown that zirconium hydrogen phosphate-modified membranes show promise as a polymer electrolyte in a hydrogen-air fuel cell membrane-electrode assembly due to a 17% higher maximum specific power compared to the original MF‑4SK membrane. This fact can be explained by an almost twofold lower ohmic resistance and reduced contribution of kinetic limitations of the membrane-electrode assembly (MEA) with the modified membranes, compared to the unmodified membrane, revealed by analysis of its impedance spectra.

t—Palladium-containing membranes are used for hydrogen separation and purification. However, for sufficiently thin membranes permeation flux can be limited by the kinetics of surface processes. In the present study, in order to overcome the limitation of transition through the surface, the developed Pd₇₆Ag₁₄Au₁₀ alloy membranes were modified with a nanostructured surface layer. The modification was carried out by the deposition of penta-branched bimetallic Pd–Pt nanoparticles on the membrane surface. An increase in hydrogen flux was observed in a wide temperature range (25–400°C). The highest values of permeation flux density were demonstrated for membranes with a penta-branched modifier, up to 52.43 mmol s^–1 m^–2 at 400°С. It is assumed that the complex morphology of the nanoparticles, as well as the presence of synergistic effect from the combination of Pd and Pt, contribute to a decrease in activation barriers and an increase in catalytic activity. The developed membranes demonstrated high and stable selectivity over time, which opens up wide possibilities for their use in steam reforming reactors for producing high-purity hydrogen.

This work is aimed at studying the characteristics of a homogeneous perfluorinated membrane at various stages of introducing zirconium hydrogen phosphate (ZrHP) in situ. A sample modified with ZrHP by pore-filling method, a sample processed the same as the first one, excluding treating with ZrHP precursor solution, and a sample of initial membrane are studied. A significant increase in the diffusion permeability and specific conductivity of the membrane in the solutions of hydrochloric acid after its treatment with heated immersion solutions is observed. This effect reduces after ZrHP nanoparticles appearance. The transport-structural parameters of the microheterogeneous model have been calculated. Both the internal equilibrium solution volume and the mobility of coions and counterions in the gel phase increase after treating with immersion solutions, due to greater swelling of the gel phase in alcohols. The specific power density of the PEMFC MEA with the ZrHP-modified membrane used as a polymeric electrolyte is significantly lower compared to the initial membrane, but annealing the membrane compensates this effect.

The effect of the anion-exchange layer of the copolymer N,N-diallyl-N,N-dimethylammonium chloride and ethyl methacrylate on the electrochemical properties of a homogeneous cation-exchange membrane based on perfluorosulfonic polymer has been studied. The application of a modifying layer with a thickness of 5 µm onto a 215 µm-thick membrane leads to a reduction in electrical conductivity by no more than 35%, while the diffusion permeability decreases more than fivefold and becomes independent of concentration. During testing of both cation-exchange and bilayer membranes in the process of limiting concentration of sodium chloride solution, comparable degrees of concentration have been achieved. The effectiveness of the bilayer membrane for selective limiting electrodialysis concentration has been demonstrated. When concentrating a solution containing sodium and calcium chlorides, the specific selective permeability coefficient P(Na⁺/Ca²⁺) for the cation-exchange membrane has ranged from 0.5 to 1.2. The use of the bilayer membrane significantly increase the specific selective permeability coefficient to 1.5–2.7, depending on the current density, allowing for efficient separation of electrolytes containing singly and doubly charged cations.

Previously published experimental data and new data on cloud points were used to plot ternary phase diagram with temperature axis for the poly(vinylidene fluoride) (PVDF)–dimethyl acetamide (DMAc)–water system. The topology of the plotted diagram is different from the published previously. It shows that an increase in temperature leads to a shift of the boundary curves (liquid equilibrium binodal, polymer crystallization curve and swelling curve) to the composition range enriched by the non-solvent. At the same time, a decrease in temperature leads to degeneration of liquid equilibrium binodal. Taking into account the plotted diagram, the expected morphologies of the membranes prepared via non-solvent induced phase separation (NIPS) in both isothermal and non-isothermal conditions were derived. Morphology and properties of the samples prepared from the dope solution of defined composition via NIPS at different temperatures and via thermally assisted non-solvent induced phase separation, T-NIPS (or NIPS in non-isothermal conditions) were studied. It was shown that an increase in temperature leads to formation of cellular structure, resulting from the liquid–liquid phase separation; a decrease in through pore size and improvement of the mechanical properties. Decrease in pore size from 110 to 35 nm accompanied with decrease in permeance from 8.1 to 0.25 L/(m² h bar) and increase in blue dextran rejection from 20 to 94%. A decrease in temperature changes the structure formation process from liquid–liquid phase separation (induced by the mass transfer processes) to solid–liquid phase separation (induced by temperature decrease). In the T-NIPS process (cooling) layers with finger-like pores and sponge-like structure between them, with spherulites surrounded by sponge-like structure and with spherulites connected with each other were formed in the structure of the membrane. T-NIPS process allows to obtain membranes with permeance 6.1 L/(m² h bar) and Blue dextran rejection of 91%.

The degree of swelling of the lithium form of the perfluorosulfonic acid membrane Nafion in alcohols (ethanol, 2-propanol), water-alcohol mixtures, and highly polar aprotic solvents (N,N-dimethylformamide (DMF) and N-methyl-2-pyrrolidone (NMP)) was studied, as well as the thermodynamics of membrane-solvent interaction using microcalorimetry. It was shown that the equilibrium swelling degree of the membrane correlates with the donor number of the solvent and the enthalpy of polymer swelling. The enthalpy of membrane swelling in all studied solvents is negative, indicating polymer solvation. Concentration dependences of the swelling and mixing enthalpies in DMF and NMP were studied in greater detail. The negative values of the swelling enthalpy across the entire concentration range of the solvents indicate good thermodynamic compatibility of the membrane with the solvent and highlight the advantage of using these solvents to produce Nafion dispersions due to their strong solvating properties.

A method has been developed for calculating the rate constants of rate-limiting steps of the water splitting reaction in the generating contacts of heterogeneous bipolar membranes (BPMs) containing particles of a catalytic additive. The method is based on the use of the equation of the current–voltage characteristic of the bipolar region of a heterogeneous BPM that contains generating contacts of two types. For the case when the catalytic additive is a cation exchanger (CE), one of the contacts is formed by CE particles and anion exchanger (AE) particles contained in BPM layers, and the other is formed by catalytic additive particles and AE particles contained in BPM layers. The order of the rate constants for the rate-limiting steps of the water splitting reaction in the studied membranes is consistent with the catalytic activity series, the constants of which are calculated based on the proton transfer reactions between water molecules and ionogenic groups contained in the BPM layers.

The rapidly growing field of portable energy sources requires the search for and development of efficient materials for such devices. To enhance the safety of the most common metal-ion batteries (lithium-ion and sodium-ion), it has been proposed to replace the liquid electrolyte with a unipolar conductive gel-polymer electrolyte based on a Nafion-like electrolyte (Inion) plasticized with aprotic solvents. This study presents the results of investigating the thermal stability, molecular and supramolecular structure, as well as the ionic conductivity of Inion membranes in lithium and sodium forms plasticized with propylene carbonate, using methods including synchronous thermal analysis, IR spectroscopy, small-angle X-ray scattering (SAXS), and impedance spectroscopy.

Tartrate stabilization of wine materials by electrodialysis makes it possible to speed up and automate this process and reduce the loss of valuable components. Widespread implementation of electrodialysis in industrial wine production is hampered by fouling of ion-exchange membranes with wine components and by the very limited range of membranes currently used. This study is devoted to a comparative analysis of properties of relatively inexpensive heterogeneous ion-exchange membranes MA-41, MK-40, AMH-PES, and CMH-PES before and after their use in tartrate stabilization of wine materials by electrodialysis. It is shown that the mechanisms of fouling and its effect on transport characteristics, as well as on the development of electroconvection and generation of H⁺ and OH^– ions, are largely determined by counterions that are transferred through cation-exchange (transition metal cations) and anion-exchange (carboxylic acid anions) membranes. Membranes MA-41 and MK-40 demonstrate higher resistance to fouling during operation of an electrodialysis device for less than 15 h.