Characterization Of Ion-exchange Membranes Research Articles

The Effect of Lactose on the Transport Properties of Ion-Exchange Membranes

The influence of lactose on the basic transport characteristics of ion exchange membranes, including cation-exchange membranes modified by polyaniline, has been studied. A positive effect on biofouling by Bacillus sp. or Shewanella oneidensis MR-1 cell cultures of modified MK-40 and Ralex CMHPES membranes has been found. That is mainly due to the different area of the conductive surface of these membranes. It has been revealed that the presence of lactose in a solution leads to a decrease in the conductivity of all studied membranes. However, the most significant effect is manifested for MK-40 membrane modified by polyaniline: its electrical conductivity is reduced by 15–25%. The diffusion permeability of the anion-exchange and initial cation-exchange membranes is poorly dependent on the presence of lactose in the solution. However, its decrease is observed by 2–2.5 times in the case of cation-exchange membranes modified by polyaniline. A significant effect of lactose on the current-voltage characteristics of the anion-exchange membranes has been found. This fact indicates significant adsorption of lactose on membrane surface in an external electric field. It is shown that ion-exchange membranes remain quite effective for electrodialysis of hydrochloric serum solutions, but their use is more effective at under limiting current modes.

Desalination of Neutral Amino Acid Solutions in an Electromembrane System.

This article’s main focus is to highlight significant aspects of amino acid solution demineralization. The main part of the amino acid production method requires the provision of downstream treatment solutions for the process of desalination. Electrodialysis (ED) and electrodeionization (EDI) are prospective technologies for such treatment. The article presents a brief review of the first studies and current research on electromembrane desalination of amino acid solutions as well as the analysis of some electrochemical features for the mineral salt–amino acid system (model solution) in an ED process based on the experimental results. The influence of various factors on the desalination of neutral amino acid-containing solutions and on target product losses in this process is estimated. The behavior of aliphatic (alanine) and aromatic (phenylalanine) amino acids in the electromembrane system is considered in mixed solutions with inorganic electrolytes. The influence of various mineral cations (Na+, K+ and NH4+) and anions (NO3−, SO42−, Cl−) on the features of the transport and current–voltage characteristics of ion-exchange membranes in the electrodialysis of phenylalanine- and alanine-containing solutions is considered. A comparative analysis of the desalination parameters of AA solutions in electrodialysis with the following pairs of heterogeneous MA-41/MK-40, MA-40/MK-40 and homogeneous AMT/CMT membranes is carried out. The minimum amount of amino acid loss along with rather high values of the degree of desalination are revealed in electrodialysis with polypropylene spacers in comparison with EDI, ED with a copolymer of styrene and divinylbenzene as spacer, as well as ED with a smooth deionization channel. At the same time, EDI is the most promising method to reach the highest desalination degree in the considered range of mineral salt content.

Ion Transport Characteristics in Membranes for Direct Formate Fuel Cells.

Ion exchange membranes are widely used in fuel cells to physically separate two electrodes and functionally conduct charge-carrier ions, such as anion exchange membranes and cation exchange membranes. The physiochemical characteristics of ion exchange membranes can affect the ion transport processes through the membrane and thus the fuel cell performance. This work aims to understand the ion transport characteristics through different types of ion exchange membrane in direct formate fuel cells. A one-dimensional model is developed and applied to predict the polarization curves, concentration distributions of reactants/products, distributions of three potentials (electric potential, electrolyte potential, and electrode potential) and the local current density in direct formate fuel cells. The effects of the membrane type and membrane thickness on the ion transport process and thus fuel cell performance are numerically investigated. In addition, particular attention is paid to the effect of the anion-cation conducting ratio of the membrane, i.e., the ratio of the anionic current to the cationic current through the membrane, on the fuel cell performance. The modeling results show that, when using an anion exchange membrane, both formate and hydroxide concentrations in the anode catalyst layer are higher than those achieved by using a cation exchange membrane. Although a thicker membrane better alleviates the fuel crossover phenomenon, increasing the membrane thickness will increase the ohmic loss, due to the enlarged ion-transport distance through the membrane. It is further found that increasing the anion-cation conducting ratio will upgrade the fuel cell performance via three mechanisms: (i) providing a higher ionic conductivity and thus reducing the ohmic loss; (ii) enabling more OH− ions to transport from the cathode to the anode and thus increasing the OH− concentration in the anode catalyst layer; and (iii) accumulating more cations in the anode and thus enhancing the formate-ion migration to the anode catalyst layer for the anodic reaction.

Characterization of Ion Exchange Membranes with Special Surface Structure

This article focuses on the preparation of the heterogeneous ion exchange membrane with a special surface structure made with three types of knitted fabric. The special surface structure of ion exchange membranes can be useful for the intensification of mass transfer processes in electrodialysis.Three types of structured ion exchange membranes were prepared together with a membrane with a flat surface to compare the influence of geometrical structures on the behaviour of ion exchange membrane properties. Electrochemical, mechanical and physical properties were determined. Structured membranes exhibited comparable electrochemical and physical properties to the flat ion exchange membrane. Some transport parameters were measured in an electrodialysis stack with two concentrations of solution. Two electrodialysis stacks with different sizes of active area were used for comparison. Improving efficiency and mass flux was not confirmed. It was not demonstrated that structured IEMs were not better than IEMs with the flat surface.

Asymmetry of current-voltage characteristics of ion-exchange membranes: Model of charge density of fixed groups linear by membrane thickness

The model of a finely porous membrane with a linear distribution of charges of its fixed groups along its depth is used in the work to explain the phenomenon of asymmetry of current-voltage characteristics of perfluorinated MF-4SK membranes surface–modified by polyaniline or halloysite nanotubes. A new exact analytical method of solution of a system of transport equations is suggested that is based on the assumption of the monotonous behavior of the electric potential inside the membrane and allows finding current- voltage characteristics (CVCs) of the membrane using a system of two implicit algebraic equations. Algebraic equations for limiting currents are obtained for the first time for different orientations of the anisotropic membrane in an electrodyalisis cell and existence of two inflection points in CVCs is explained when its less charge side is oriented towards the anode.

Development of Cost-Effective Ion-Exchange Membranes for High Performance Reverse Electrodialysis

Reverse electrodialysis (RED) is one of the promising processes for generating electricity from the salt concentration gradient between river and sea water. A RED stack contains alternately arranged anion- and cation-exchange membranes (AEMs and CEMs, respectively) which separate salt solutions of different concentrations. The power generation performance of REDs significantly depends on the characteristics of ion-exchange membranes (IEMs). The important membrane properties dominating the power generation in RED processes are the ion-exchange capacity, water swelling degree, electrical resistance, permselectivity, membrane thickness, and surface morphology etc. Moreover, the cost-effectiveness of IEMs is the most significant factor determining the successful commercialization of the RED process. In recent years, pore-filled IEMs (PFIEMs) in which an inert porous substrate provides excellent mechanical and chemical stabilities while a filling ionomer selectively transports ions through the membrane have been receiving great interests in the application to various energy conversion processes such as fuel cells and redox flow batteries. Simple and cheap mass production by a roll-to-roll process is one of the main advantages of the PFIEMs. In this work, we have investigated the optimum design parameters of the PFIEMs for successful application to a RED process. In addition, we have studied on the surface modification of the PFIEMs through facile methods for the improvement of the membrane properties. (This work was supported in part by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Korea government (MSIP) (2015R1A1A1A05001486) and the Technology Innovation Program funded by the Korea government (MOTIE) (No. 10047796).)

How Operational Parameters and Membrane Characteristics Affect the Performance of Electrodialysis Reversal Desalination Systems: The State of the Art

Operating parameters and membrane characteristics strongly affect the performance of electrodialysis reversal systems. The most impactful factors are applied voltage, flow rate, temperature, initial feed composition, and ion exchange membrane characteristics; the pH of the feed also has an effect, although to a lesser extent. To determine more precisely how all of these factors impact performance – especially as measured by desalination rate and the quality of the desalinated water – several valuable studies have been conducted. However, no comprehensive paper has been published, and some researchers have reported different findings from differently designed electrodialysis reversal systems. Therefore, to synthesize previous research and reconcile superficially disparate findings, this review discusses, analyzes, and summarizes the results from the literature. Such a review can help researchers and technicians optimize electrodialysis reversal systems and improve the quality of desalted water.

Asymmetry of current–voltage characteristics: a bilayer model of a modified ion-exchange membrane

The asymmetry of the current–voltage characteristics of ion-exchange membranes is explained in terms of the model of a bilayer fine porous membrane with constant charge distributions over the thickness of layers. This model has previously been proposed for determining diffusion permeability of membranes. In the case of one uncharged (neutral) layer, a set of two implicit algebraic equations is derived for determining the total current–voltage characteristics (CVC) of a membrane. For the first time, implicit algebraic equations are obtained for calculating the limiting currents at different orientations of an anisotropic membrane in an electrodialysis cell and explicit expressions are derived for determining specific conductivity of the membrane from the slope of the ohmic region of a CVC under the approximation of “excluded coions.” The model may be successfully used for describing the CVCs of perfluorinated MF-4SC sulfonic cation-exchange membranes, the surface layers of which are modified with polyaniline or halloysite.

Mechanical testing of small, thin samples in a humidity-controlled oven

A new fixture for the mechanical characterization of thin polymer films under controlled temperature and relative humidity conditions is reported. Novel conducting polymers are often synthesized in small quantities and processed into films on the order of 10–100 microns thick. Standard tensile tests do not allow for adequate testing of these small sample sizes. Hence, a modification of the Sentmanat Extensional Rheometer (SER) to perform tensile testing on thin membranes is presented. Since the standard L-shaped pins do not secure thin polymer films at lower temperatures (i.e., below the melting point), screw down clamps were created to allow for mechanical characterization of solid polymer films. The new testing apparatus allows for mechanical characterization with as little as 2 % of the material needed for testing on a traditional tensile tester. In a parallel effort, a humidity delivery system developed for the TA Instruments ARES-G2 rheometer allows for testing at a range of temperatures (30–100 °C) and relative humidity conditions (0–95 % RH). The novel oven was benchmarked with low density polyethylene and Nafion 115Ⓡ. While the new experiment was built for characterization of ion exchange membranes for fuel cells, the oven is capable of characterizing any environmentally sensitive material using all standard rheometer geometries.

Characterization of Ion Exchange Membrane Based on Hydrocarbon Based Polymer and Functional Additives

A sol-gel method and an in situ method were used to synthesize organic-inorganic composite membranes based on poly(arylene ether sulfone) (SPAES), phosphotungstic acid (PWA) containing sulfonic acid and amine groups. HPA is generally water soluble and causing a deterioration of cell performance. To solve this problem, PWA particles were functionalized with various silane compounds to enhance proton conductivity and to possess insoluble property in water. This study compares the performance of polymer electrolyte membrane fuel cells with different preparation methods for the membrane and composite PWA-silica-SO3H particles. The optimum composition of PWA-silica-SO3H and effect of amine groups in SPAES composite membrane are determined on the basis of the mechanical properties, the behavior of water in the membrane, and the level of proton conductivity. The mechanical properties of the composite membrane prepared by sol-gel method were improved with the introduction of PWA-silica-SO3H particles. Also, the sol-gel composite membrane containing amine groups has higher levels of proton conductivity than the other composite membranes. An increase in the silica content of the PWA-silica sol-gel particles increases the ion conductivity because the inorganic component and the incorporation of PWA lead to a high concentration of functional.

The Electrochemical Characterization of Ion Exchange Membranes in Different Electrolytic Environments: Investigation of Concentration and pH Effects

In this research, the effect of electrolyte concentration and environmental pH variations on electrochemical properties of two commercial heterogeneous ion exchange membranes was studied. Membrane structure investigation was carried out using the SEM method. Obtained images showed that the anion-exchange membrane possesses a rough surface while the cation-exchange one has mainly a smooth surface with effect on ions transportation ability. Membrane potential, transport number, and permselectivity were initially improved in cation-exchange membrane with an increase of electrolyte concentration from 0.1 to 0.5 M and then began to decrease with higher concentration increase from 0.5 to 1.0 M. Also, membrane potential, transport number, and permselectivity were decreased in anion-exchange membrane with increase of electrolyte concentration. Results revealed that cation-exchange membrane had higher potential, transport number, and selectivity at pH 7 and the anion-exchange one showed better performance at pH 10 compared to other pH values. Membrane resistance was decreased in both membranes due to increase of electrolyte concentration. Resistance also increased initially with increase of pH value but then began to decrease with higher increase in pH value. Membranes exhibited higher selectivity for monovalent ions compared to bivalent one. The results demonstrate that the anion-exchange membrane has lower selectivity and electrical resistance compared to the cation-exchange membrane.

Substantiation of proposals on standardization of the manganese content in water supplied for electrodyalysis treatment

The results of systematic investigations of the electrodialysis process of manganese-containing solutions and the impact of manganese compounds on electrochemical characteristics of ion-exchange membranes have been analyzed. New approaches to the standardization of the manganese content in the water supplied for electrodialysis desalination were proposed on the basis of the conducted analysis.

Preparation and characterization of ion-exchange membrane using Sty/HEA/LMA terpolymer via post-sulfonation

An ion-exchange membrane based on a styrene/hydroxyethyl acrylate/lauryl methacrylate (Sty/HEA/LMA) terpolymer was prepared via a post-sulfonation reaction for various sulfonation times. Sulfonic groups were introduced into the membrane structure with sulfuric acid as the sulfonating agent and silver sulfate as an initiator. Sulfonated Sty/HEA/LMA membranes were characterized by Fourier transform infrared spectrometry (FT-IR) and nuclear magnetic resonance (NMR), as well as by determining the degree of sulfonation (DS), ion-exchange capacity (IEC), water uptake (WU) and electrical property of the membranes. The presence of sulfonic groups in the sulfonated Sty/HEA/LMA membranes was confirmed by FT-IR, and the resulting membrane showed an ion-exchange capacity of 0.812 meq/g and an electrical resistance of 0.3 Ω cm 2. Water uptake of the prepared membranes increased with the degree of sulfonation at the reaction time. The surface morphology obtained by AFM clearly showed an increase of roughness with sulfonation reaction time. The elongation of the Sty/HEA/LMA ion-exchange membranes were improved with the increasing LMA content compared to sulfonated polystyrene membrane.

Preparation and Characterization of Ion Exchange Membranes for Redox Flow Battery

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Determination of structural, selective, electrokinetic and percolation characteristics of ion-exchange membranes from conductive data

The structural, selective and electrokinetic characteristics and percolation parameters were determined for different ion-exchange polymer membranes from their conductivity data using the two-phase model of membrane conductivity and percolation theory. The two different combinations of micro-phases in IEM, used in the two-phase conductivity model and percolation theory are presented and discussed. Based on this two-phase model and concentration dependences of membrane conductivity, the structural membrane heterogeneity was determined for 14 commercial IEMs. The diffusion coefficient, molar conductivity of counter-ions and hydration capacity of the gelphase were calculated and analyzed for cross-linked and linear ion-exchange polymers. The ion-exchange equilibrium constants for MK-40 were estimated from values of membrane conductivity at the iso-conductance point in individual electrolyte solutions and their mixtures. The percolation theory was used to describe the conductivity of different membrane compositions with various volume fraction of the conducting phase. The estimation of φ cr and γ percolation parameters showed that the obtained values of critical index γ agree with the theory for investigated materials, and the value of the threshold parameter φ cr depends on the preparation method and structural heterogeneity of a given composition.

06/01900 Experimental studies of a direct methanol fuel cell: Ge, J. and Liu, H. Journal of Power Sources, 2005, 142, (1–2), 56–69

In direct methanol fuel cells (DMFCs), the optimum characteristics of ion-exchange membranes are investigated at high concentrations of methanol feed up to 7 M by modifying the diffusion coefficient and the ionic conductivity of the polyelectrolyte material. A Nafion membrane is modified by the incorporation of layered double hydroxide (LDH) nanoplatelets with different Mg2+:Al3+ ratios. When the feed concentration of methanol is lower than 3 M, the DMFC is controlled by the ionic conductivity of the polyelectrolyte membrane because methanol cross-over is not relatively significant. When the feed concentration is high, however, the diffusion coefficient of methanol is the key factor that determines the performance of the fuel cell. This is due to a high concentration gradient of methanol across the polyelectrolyte membrane. The open-circuit voltage is increased by the decreased diffusion coefficient in LDH/Nafion nanocomposite membranes at methanol feed concentrations up to 7 M; apparently because methanol cross-over is suppressed by the incorporation of LDH. The maximum power density of the DMFC is determined by the two competing transport processes of ion conduction and methanol diffusion, especially at a relatively high methanol concentration, that can provide optimum operating conditions in the membrane.

06/01906 Preparation of carbon-supported PtRu nanoparticles for direct methanol fuel cell applications — a comparative study: Deivaraj, T. C. and Lee, J. Y. Journal of Power Sources, 2005, 142, (1–2), 43–49

In direct methanol fuel cells (DMFCs), the optimum characteristics of ion-exchange membranes are investigated at high concentrations of methanol feed up to 7 M by modifying the diffusion coefficient and the ionic conductivity of the polyelectrolyte material. A Nafion membrane is modified by the incorporation of layered double hydroxide (LDH) nanoplatelets with different Mg2+:Al3+ ratios. When the feed concentration of methanol is lower than 3 M, the DMFC is controlled by the ionic conductivity of the polyelectrolyte membrane because methanol cross-over is not relatively significant. When the feed concentration is high, however, the diffusion coefficient of methanol is the key factor that determines the performance of the fuel cell. This is due to a high concentration gradient of methanol across the polyelectrolyte membrane. The open-circuit voltage is increased by the decreased diffusion coefficient in LDH/Nafion nanocomposite membranes at methanol feed concentrations up to 7 M; apparently because methanol cross-over is suppressed by the incorporation of LDH. The maximum power density of the DMFC is determined by the two competing transport processes of ion conduction and methanol diffusion, especially at a relatively high methanol concentration, that can provide optimum operating conditions in the membrane.

Optimum ionic conductivity and diffusion coefficient of ion-exchange membranes at high methanol feed concentrations in a direct methanol fuel cell

In direct methanol fuel cells (DMFCs), the optimum characteristics of ion-exchange membranes are investigated at high concentrations of methanol feed up to 7 M by modifying the diffusion coefficient and the ionic conductivity of the polyelectrolyte material. A Nafion membrane is modified by the incorporation of layered double hydroxide (LDH) nanoplatelets with different Mg 2+:Al 3+ ratios. When the feed concentration of methanol is lower than 3 M, the DMFC is controlled by the ionic conductivity of the polyelectrolyte membrane because methanol cross-over is not relatively significant. When the feed concentration is high, however, the diffusion coefficient of methanol is the key factor that determines the performance of the fuel cell. This is due to a high concentration gradient of methanol across the polyelectrolyte membrane. The open-circuit voltage is increased by the decreased diffusion coefficient in LDH/Nafion nanocomposite membranes at methanol feed concentrations up to 7 M; apparently because methanol cross-over is suppressed by the incorporation of LDH. The maximum power density of the DMFC is determined by the two competing transport processes of ion conduction and methanol diffusion, especially at a relatively high methanol concentration, that can provide optimum operating conditions in the membrane.

Effects of inorganic substances on water splitting in ion-exchange membranes: I. Electrochemical characteristics of ion-exchange membranes coated with iron hydroxide/oxide and silica sol

The effects of inorganic substances on water splitting in ion-exchange membranes (IEMs) were investigated. In this study, iron hydroxide/ oxide and silica sol were immobilized on the surface of the IEMs. The water-splitting capabilities of the metal-embedded cation-exchange membranes were 10 4–10 5 times greater than those of the virgin membranes at the same current density. Similarly, silica sol (i.e., SiOH groups) deposited on the anion-exchange membrane surface also drastically increased the proton transport numbers. It was thought that the bipolar structure consisting of H- and OH-affinity groups immobilized on the IEM surface increased water-splitting due to the enhancement of water polarization with the help of strong electric fields. This study revealed that metal oxides or silica groups (SiOH), as well as metal hydroxides, can be used as catalysts for water splitting.

Development of urethane acrylate composite ion-exchange membranes and their electrochemical characterization

With the objective of introducing antifouling characteristics into interpolymer types of cation and anion exchange membranes, the surface of these membranes was coated with a 12-μm-thick urethane acrylate layer and was cured by UV radiation of wavelengths 308 and 172 nm under a complete inert atmosphere. Different urethane acrylate composite ion exchange membranes developed were characterized in NaCl solution by measuring their ion-exchange capacity, volume fraction of water, contact angle with water, membrane conductance, and membrane potential. It was found that the electrochemical transport properties of urethane acrylate composite cation-exchange membranes were increased due to resonance stabilization of the urethane group, which acts as a weak acid and dissociates as a negatively charged urethane ion and a positively charged proton. This contributes toward the net charge density of the membrane matrix responsible for enhanced selectivity and conductivity, while for urethane acrylate composite anion-exchange membranes reduction in net charge density was responsible for reduction in electrochemical transport properties. Counterion transport number, permselectivity, and counterion diffusion coefficient values for these membranes were also estimated. Experiments were also carried out in higher homologs of sodium carboxylate solutions in order to observe the fouling tendencies of these membranes. It was concluded that it is possible to obtain antifouling characteristics of ion-exchange membranes by coating and curing thin hydrophilic layers of urethane acrylate on their surfaces without sacrificing their electrochemical transport properties.