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19 pages, 5253 KiB

Open AccessArticle

Elucidating the Mechanism of Electro-Adsorption on Electrically Conductive Ultrafiltration Membranes via Modified Poisson-Boltzmann Equation

by Muhammad Usman, Shahrokh Vahedi, Sarah Glass, Volkan Filiz and Mathias Ernst

Membranes 2024, 14(8), 175; https://doi.org/10.3390/membranes14080175 - 10 Aug 2024

Viewed by 1005

Abstract

Electrically conductive membranes (ECMs) were prepared by coating porous ethylenediamine-modified polyacrylonitrile (PAN-EDA) UF membranes with an ultrathin layer of platinum (Pt) nanoparticles through magnetron sputtering. These ECMs were used in electrofiltration to study the removal of brilliant blue dye from an aqueous solution [...] Read more.

Electrically conductive membranes (ECMs) were prepared by coating porous ethylenediamine-modified polyacrylonitrile (PAN-EDA) UF membranes with an ultrathin layer of platinum (Pt) nanoparticles through magnetron sputtering. These ECMs were used in electrofiltration to study the removal of brilliant blue dye from an aqueous solution under positive electrical potentials (0–2.5 V). Negative electrical potentials (−1.0–−2.5 V) were also investigated to regenerate the membrane by desorbing the dye from the ECM surface. At +0 V, the EC PAN-EDA membrane adsorbed the dye due to its intrinsic positive charge. Application of −2.0 V resulted in a maximum of 39% desorption of the dye. A modified Poisson-Boltzmann (MPB) model showed that −2.0 V created a repulsive force within the first 24 nm of the membrane matrix, which had a minimal effect on dye ions adsorbed deeper within the membrane, thus limiting the electro-desorption efficiency to 39%. Moreover, increasing positive potentials from +0.5 V to +2.5 V led to increased dye electro-adsorption by 9.5 times, from 132 mg/m² to 1112 mg/m² at pH 8 (equivalent to the membrane’s isoelectric point). The MBP simulations demonstrated that increasing electro-adsorption loadings are related to increasing attractive force, indicating electro-adsorption induced by attractive force is the dominant mechanism and the role of other mechanisms (e.g., electrochemical oxidation) is excluded. At pH 5, electro-adsorption further increased to 1390 mg/m², likely due to the additional positive charge of the membrane (zeta potential = 9.2 mV) compared to pH 8. At pH 8, complete desorption of the dye from the ECM surface was achieved with a significant repulsive force at −2.0 V. However, as pH decreased from 8 to 5, the desorption efficiency decreased by 3.9% due to the membrane’s positive charge. These findings help elucidate the mechanisms of electro-adsorption and desorption on ECMs using dye as a model for organic compounds like humic acids. Full article

(This article belongs to the Special Issue Electrochemical Membranes: Materials, Characterization, Testing, and Cleaning)

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17 pages, 1884 KiB

Open AccessArticle

Electrochemical Characterization of Charged Membranes from Different Materials and Structures via Membrane Potential Analysis

by Virginia Romero, Lourdes Gelde and Juana Benavente

Membranes 2023, 13(8), 739; https://doi.org/10.3390/membranes13080739 - 17 Aug 2023

Viewed by 1811

Abstract

Electrochemical characterization of positively and negatively charged membranes is performed by analyzing membrane potential values on the basis of the Teorell–Meyer–Sievers (TMS) model. This analysis allows the separate estimation of Donnan (interfacial effects) and diffusion (differences in ions transport through the membrane) contributions, [...] Read more.

Electrochemical characterization of positively and negatively charged membranes is performed by analyzing membrane potential values on the basis of the Teorell–Meyer–Sievers (TMS) model. This analysis allows the separate estimation of Donnan (interfacial effects) and diffusion (differences in ions transport through the membrane) contributions, and it permits the evaluation of the membrane’s effective fixed charge concentration and the transport number of the ions in the membrane. Typical ion-exchange commercial membranes (AMX, Ionics or Nafion) are analyzed, though other experimental and commercial membranes, which are derived from different materials and have diverse structures (dense, swollen or nanoporous structures), are also considered. Moreover, for some membranes, changes associated with different modifications and other effects (concentration gradient or level, solution stirring, etc.) are also analyzed. Full article

(This article belongs to the Special Issue Electrochemical Membranes: Materials, Characterization, Testing, and Cleaning)

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14 pages, 3448 KiB

Open AccessArticle

Graphene Oxide/Polyethyleneimine-Modified Cation Exchange Membrane for Efficient Selective Recovery of Ammonia Nitrogen from Wastewater

by Yuanyuan Yu, Qin Zeng, Haoquan Zhang, Maoqin Ao, Jingmei Yao, Chun Yang, Svetlozar Velizarov and Le Han

Membranes 2023, 13(8), 726; https://doi.org/10.3390/membranes13080726 - 10 Aug 2023

Viewed by 1395

Abstract

Competition for the migration of interfering cations limits the scale-up and implementation of the Donnan dialysis process for the recovery of ammonia nitrogen (NH₄⁺-N) from wastewater in practice. Highly efficient selective permeation of NH₄⁺ through a cation exchange [...] Read more.

Competition for the migration of interfering cations limits the scale-up and implementation of the Donnan dialysis process for the recovery of ammonia nitrogen (NH₄⁺-N) from wastewater in practice. Highly efficient selective permeation of NH₄⁺ through a cation exchange membrane (CEM) is expected to be modulated via tuning the surface charge and structure of CEM. In this work, a novel CEM was designed to form a graphene oxide (GO)-polyethyleneimine (PEI) cross-linked layer by introducing self-assembling layers of GO and PEI on the surface of a commercial CEM, which rationally regulates the surface charge and structure of the membrane. The resulting positively charged membrane surface exhibits stronger repulsion for divalent cations compared to monovalent cations according to Coulomb’s law, while, simultaneously, GO forms π–metal cation conjugates between metal cations (e.g., Mg²⁺ and Ca²⁺), thus limiting metal cation transport across the membrane. During the DD process, higher NH₄⁺ concentrations resulted in a longer time to reach Donnan equilibrium and higher NH₄⁺ flux, while increased Mg²⁺ concentrations resulted in lower NH₄⁺ flux (from 0.414 to 0.213 mol·m⁻²·h⁻¹). Using the synergistic effect of electrostatic interaction and non-covalent cross-linking, the designed membrane, referred to as GO-PEI (20) and prepared by a 20 min impregnation in the GO-PEI mixture, exhibited an NH₄⁺ transport rate of 0.429 mol·m⁻²·h⁻¹ and a Mg²⁺ transport rate of 0.003 mol·m⁻²·h⁻¹ in single-salt solution tests and an NH₄⁺/Mg²⁺ selectivity of 15.46, outperforming those of the unmodified and PEI membranes (1.30 and 5.74, respectively). In mixed salt solution tests, the GO-PEI (20) membrane showed a selectivity of 15.46 (~1.36, the unmodified membrane) for NH₄⁺/Mg²⁺ and a good structural stability after 72 h of continuous operation. Therefore, this facile surface charge modulation approach provides a promising avenue for achieving efficient NH₄⁺-selective separation by modified CEMs. Full article

(This article belongs to the Special Issue Electrochemical Membranes: Materials, Characterization, Testing, and Cleaning)

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11 pages, 7089 KiB

Open AccessArticle

Simultaneous Urea and Phosphate Recovery from Synthetic Urine by Electrochemical Stabilization

by László Koók, Kristóf Bence Nagy, Ilona Nyirő-Kósa, Szilveszter Kovács, Jan Žitka, Miroslav Otmar, Péter Bakonyi, Nándor Nemestóthy and Katalin Bélafi-Bakó

Membranes 2023, 13(8), 699; https://doi.org/10.3390/membranes13080699 - 27 Jul 2023

Viewed by 1395

Abstract

Urine is a widely available renewable source of nitrogen and phosphorous. The nitrogen in urine is present in the form of urea, which is rapidly hydrolyzed to ammonia and carbonic acid by the urease enzymes occurring in nature. In order to efficiently recover [...] Read more.

Urine is a widely available renewable source of nitrogen and phosphorous. The nitrogen in urine is present in the form of urea, which is rapidly hydrolyzed to ammonia and carbonic acid by the urease enzymes occurring in nature. In order to efficiently recover urea, the inhibition of urease must be done, usually by increasing the pH value above 11. This method, however, usually is based on external chemical dosing, limiting the sustainability of the process. In this work, the simultaneous recovery of urea and phosphorous from synthetic urine was aimed at by means of electrochemical pH modulation. Electrochemical cells were constructed and used for urea stabilization from synthetic urine by the in situ formation of OH^- ions at the cathode. In addition, phosphorous precipitation with divalent cations (Ca²⁺, Mg²⁺) in the course of pH elevation was studied. Electrochemical cells equipped with commercial (Fumasep FKE) and developmental (PSEBS SU) cation exchange membranes (CEM) were used in this study to carry out urea stabilization and simultaneous P-recovery at an applied current density of 60 A m⁻². The urea was successfully stabilized for a long time (more than 1 month at room temperature and nearly two months at 4 °C) at a pH of 11.5. In addition, >82% P-recovery could be achieved in the form of precipitate, which was identified as amorphous calcium magnesium phosphate (CMP) by using transmission electron microscopy (TEM). Full article

(This article belongs to the Special Issue Electrochemical Membranes: Materials, Characterization, Testing, and Cleaning)

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16 pages, 3812 KiB

Open AccessArticle

Proton Conducting Organic-Inorganic Composite Membranes for All-Vanadium Redox Flow Battery

by Sooraj Sreenath, Nayanthara P. Sreelatha, Chetan M. Pawar, Vidhiben Dave, Bhavana Bhatt, Nitin G. Borle and Rajaram Krishna Nagarale

Membranes 2023, 13(6), 574; https://doi.org/10.3390/membranes13060574 - 1 Jun 2023

Cited by 5 | Viewed by 1786

Abstract

The quest for a cost-effective, chemically-inert, robust and proton conducting membrane for flow batteries is at its paramount. Perfluorinated membranes suffer severe electrolyte diffusion, whereas conductivity and dimensional stability in engineered thermoplastics depend on the degree of functionalization. Herein, we report surface-modified thermally [...] Read more.

The quest for a cost-effective, chemically-inert, robust and proton conducting membrane for flow batteries is at its paramount. Perfluorinated membranes suffer severe electrolyte diffusion, whereas conductivity and dimensional stability in engineered thermoplastics depend on the degree of functionalization. Herein, we report surface-modified thermally crosslinked polyvinyl alcohol-silica (PVA-SiO₂) membranes for the vanadium redox flow battery (VRFB). Hygroscopic, proton-storing metal oxides such as SiO₂, ZrO₂ and SnO₂ were coated on the membranes via the acid-catalyzed sol-gel strategy. The membranes of PVA-SiO₂-Si, PVA-SiO₂-Zr and PVA-SiO₂-Sn demonstrated excellent oxidative stability in 2 M H₂SO₄ containing 1.5 M VO₂⁺ ions. The metal oxide layer had good influence on conductivity and zeta potential values. The observed trend for conductivity and zeta potential values was PVA-SiO₂-Sn > PVA-SiO₂-Si > PVA-SiO₂-Zr. In VRFB, the membranes showcased higher Coulombic efficiency than Nafion-117 and stable energy efficiencies over 200 cycles at the 100 mA cm⁻² current density. The order of average capacity decay per cycle was PVA-SiO₂-Zr < PVA-SiO₂-Sn < PVA-SiO₂-Si < Nafion-117. PVA-SiO₂-Sn had the highest power density of 260 mW cm⁻², while the self-discharge for PVA-SiO₂-Zr was ~3 times higher than Nafion-117. VRFB performance reflects the potential of the facile surface modification technique to design advanced membranes for energy device applications. Full article

(This article belongs to the Special Issue Electrochemical Membranes: Materials, Characterization, Testing, and Cleaning)

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14 pages, 4186 KiB

Open AccessArticle

Electrochemical Oxidation of Organic Pollutants in Aqueous Solution Using a Ti₄O₇ Particle Anode

by Andrey Kislyi, Ilya Moroz, Vera Guliaeva, Yuri Prokhorov, Anastasiia Klevtsova and Semyon Mareev

Membranes 2023, 13(5), 521; https://doi.org/10.3390/membranes13050521 - 17 May 2023

Cited by 5 | Viewed by 2202

Abstract

Anodes based on substoichiometric titanium oxide (Ti₄O₇) are among the most effective for the anodic oxidation of organic pollutants in aqueous solutions. Such electrodes can be made in the form of semipermeable porous structures called reactive electrochemical membranes (REMs). [...] Read more.

Anodes based on substoichiometric titanium oxide (Ti₄O₇) are among the most effective for the anodic oxidation of organic pollutants in aqueous solutions. Such electrodes can be made in the form of semipermeable porous structures called reactive electrochemical membranes (REMs). Recent work has shown that REMs with large pore sizes (0.5–2 mm) are highly efficient (comparable or superior to boron-doped diamond (BDD) anodes) and can be used to oxidize a wide range of contaminants. In this work, for the first time, a Ti₄O₇ particle anode (with a granule size of 1–3 mm and forming pores of 0.2–1 mm) was used for the oxidation of benzoic, maleic and oxalic acids and hydroquinone in aqueous solutions with an initial COD of 600 mg/L. The results demonstrated that a high instantaneous current efficiency (ICE) of about 40% and a high removal degree of more than 99% can be achieved. The Ti₄O₇ anode showed good stability after 108 operating hours at 36 mA/cm². Full article

(This article belongs to the Special Issue Electrochemical Membranes: Materials, Characterization, Testing, and Cleaning)

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17 pages, 4779 KiB

Open AccessArticle

Interplay between Forced Convection and Electroconvection during the Overlimiting Ion Transport through Anion-Exchange Membranes: A Fourier Transform Analysis of Membrane Voltage Drops

by Lorena Hernández-Pérez, Manuel César Martí-Calatayud, Maria Teresa Montañés and Valentín Pérez-Herranz

Membranes 2023, 13(3), 363; https://doi.org/10.3390/membranes13030363 - 21 Mar 2023

Cited by 7 | Viewed by 1627

Abstract

Electrodialysis (ED) applications have expanded in recent years and new modes of operation are being investigated. Operation at overlimiting currents involves the phenomenon of electroconvection, which is associated with the generation of vortices. These vortices accelerate the process of solution mixing, making it [...] Read more.

Electrodialysis (ED) applications have expanded in recent years and new modes of operation are being investigated. Operation at overlimiting currents involves the phenomenon of electroconvection, which is associated with the generation of vortices. These vortices accelerate the process of solution mixing, making it possible to increase the transport of ions across the membranes. In this work, frequency analysis is applied to investigate the interaction between different parameters on the development of electroconvection near anion-exchange membranes, which would provide a basis for the development of ED systems with favored electroconvection. Chronopotentiometric curves are registered and Fast Fourier Transform analysis is carried out to study the amplitude of the transmembrane voltage oscillations. Diverse behaviors are detected as a function of the level of forced convection and current density. The synergistic combination of forced convection and overlimiting currents leads to an increase in the signal amplitude, which is especially noticeable at frequencies around 0.1 Hz. Fast Fourier Transform analysis allows identifying, for a given system, the conditions that lead to a transition between stable and chaotic electroconvection modes. Full article

(This article belongs to the Special Issue Electrochemical Membranes: Materials, Characterization, Testing, and Cleaning)

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16 pages, 4520 KiB

Open AccessArticle

Energetic Valorisation of Saltworks Bitterns via Reverse Electrodialysis: A Laboratory Experimental Campaign

by Syed Abdullah Shah, Roberta Cucchiara, Fabrizio Vicari, Andrea Cipollina, Alessandro Tamburini and Giorgio Micale

Membranes 2023, 13(3), 293; https://doi.org/10.3390/membranes13030293 - 28 Feb 2023

Cited by 5 | Viewed by 2196

Abstract

Concentrated bitterns discharged from saltworks have extremely high salinity, often up to 300 g/L, thus their direct disposal not only has a harmful effect on the environment, but also generates a depletion of a potential resource of renewable energy. Here, reverse electrodialysis (RED), [...] Read more.

Concentrated bitterns discharged from saltworks have extremely high salinity, often up to 300 g/L, thus their direct disposal not only has a harmful effect on the environment, but also generates a depletion of a potential resource of renewable energy. Here, reverse electrodialysis (RED), an emerging electrochemical membrane process, is proposed to capture and convert the salinity gradient power (SGP) intrinsically conveyed by these bitterns also aiming at the reduction of concentrated salty water disposal. A laboratory-scale RED unit has been adopted to study the SGP potential of such brines, testing ion exchange membranes from different suppliers and under different operating conditions. Membranes supplied by Fujifilm, Fumatech, and Suez were tested, and the results were compared. The unit was fed with synthetic hypersaline solution mimicking the concentration of natural bitterns (5 mol/L of NaCl) on one side, and with variable concentration of NaCl dilute solutions (0.01–0.1 mol/L) on the other. The influence of several operating parameters has also been assessed, including solutions flowrate and temperature. Increasing feed solutions’ temperature and velocity has been found to lower the stack resistance, which enhances the output performance of the RED stack. The maximum obtained power density (corrected to account for the effect of electrodic compartments, which can be very relevant in five cell pairs laboratory stacks) reached around 10.5 W/m²_cellpair, with FUJIFILM Type 10 membranes, temperature of 40 °C, and a fluid velocity of 3 cm s⁻¹ (as empty channel, considering 270 μm thickness). Notably, the present study results confirm the large potential for SGP generation from hypersaline brines, thus providing useful guidance for the harvesting of SGP in seawater saltworks all around the world. Full article

(This article belongs to the Special Issue Electrochemical Membranes: Materials, Characterization, Testing, and Cleaning)

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16 pages, 3739 KiB

Open AccessArticle

Computational Design of an Electro-Membrane Microfluidic-Diode System

by Mykola Bondarenko and Andriy Yaroshchuk

Membranes 2023, 13(2), 243; https://doi.org/10.3390/membranes13020243 - 17 Feb 2023

Viewed by 1284

Abstract

This study uses computational design to explore the performance of a novel electro-membrane microfluidic diode consisting of physically conjugated nanoporous and micro-perforated ion-exchange layers. Previously, such structures have been demonstrated to exhibit asymmetric electroosmosis, but the model was unrealistic in several important respects. [...] Read more.

This study uses computational design to explore the performance of a novel electro-membrane microfluidic diode consisting of physically conjugated nanoporous and micro-perforated ion-exchange layers. Previously, such structures have been demonstrated to exhibit asymmetric electroosmosis, but the model was unrealistic in several important respects. This numerical study investigates two quantitative measures of performance (linear velocity of net flow and efficiency) as functions of such principal system parameters as perforation size and spacing, the thickness of the nanoporous layer and the zeta potential of the pore surface. All of these dependencies exhibit pronounced maxima, which is of interest for future practical applications. The calculated linear velocities of net flows are in the range of several tens of liters per square meter per hour at realistically applied voltages. The system performance somewhat declines when the perforation size is increased from 2 µm to 128 µm (with a parallel increase of the inter-perforation spacing) but remains quite decent even for the largest perforation size. Such perforations should be relatively easy to generate using inexpensive equipment. Full article

(This article belongs to the Special Issue Electrochemical Membranes: Materials, Characterization, Testing, and Cleaning)

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23 pages, 4820 KiB

Open AccessArticle

Concepts and Misconceptions Concerning the Influence of Divalent Ions on the Performance of Reverse Electrodialysis Using Natural Waters

by Joost Veerman

Membranes 2023, 13(1), 69; https://doi.org/10.3390/membranes13010069 - 5 Jan 2023

Cited by 6 | Viewed by 2339

Abstract

Divalent ions have a negative effect on the obtained power and efficiency of the reverse electrodialysis (RED) process when using natural waters. These effects can largely be attributed to the interaction between the various ions and the membranes, resulting in a decreased membrane [...] Read more.

Divalent ions have a negative effect on the obtained power and efficiency of the reverse electrodialysis (RED) process when using natural waters. These effects can largely be attributed to the interaction between the various ions and the membranes, resulting in a decreased membrane voltage, an increased membrane resistance, and uphill transport of divalent ions. The aim of this study was to investigate the causes of these differences and, if possible, to find underlying causes. The approach mainly followed that in literature articles that specifically focused on the effect of divalent ions on RED. It transpired that seven publications were useful because the methodology was well described and sufficient data was published. I found two widely shared misconceptions. The first concerns the role of the stack voltage in uphill transport of divalent ions; itis often thought that the open circuit voltage (OCV) must be taken into account, but it is plausible that the voltage under working conditions is the critical factor. The second debatable point concerns the methodology used to make a series of solutions to study the effect of divalent ions. Typically, solutions with a constant number of moles of salt are used; however, it is better to make a series with a constant ratio of equivalents of those salts. Moreover, it is plausible that the decreased voltage can be explained by the inherently lower Donnan potential of multi-charged ions and that increased resistance is caused by the fact that divalent ions—with a lower mobility there than the monovalent ions—occupy relatively much of the available space in the gel phase of the membrane. While both resistance and voltage play a decisive role in RED and probably also in other membrane processes like electrodialysis (ED), it is remarkable that there are so few publications that focus on measurements on individual membranes. The implications of these results is that research on the effect of divalent ions in RED, ED and similar processes needs to be more structured in the future. Relatively simple procedures can be developed for the determination of membrane resistance in solutions of mixtures of mono- and divalent salts. The same applies to determining the membrane potential. The challenge is to arrive at a standard method for equipment, methodology, and the composition of the test solutions. Full article

(This article belongs to the Special Issue Electrochemical Membranes: Materials, Characterization, Testing, and Cleaning)

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16 pages, 1975 KiB

Open AccessArticle

Further Development of Polyepichlorohydrin Based Anion Exchange Membranes for Reverse Electrodialysis by Tuning Cast Solution Properties

by Mine Eti, Aydın Cihanoğlu, Enver Güler, Lucia Gomez-Coma, Esra Altıok, Müşerref Arda, Inmaculada Ortiz and Nalan Kabay

Membranes 2022, 12(12), 1192; https://doi.org/10.3390/membranes12121192 - 26 Nov 2022

Cited by 3 | Viewed by 2229

Abstract

Recently, there have been several studies done regarding anion exchange membranes (AEMs) based on polyepichlorohydrin (PECH), an attractive polymer enabling safe membrane fabrication due to its inherent chloromethyl groups. However, there are still undiscovered properties of these membranes emerging from different compositions of [...] Read more.

Recently, there have been several studies done regarding anion exchange membranes (AEMs) based on polyepichlorohydrin (PECH), an attractive polymer enabling safe membrane fabrication due to its inherent chloromethyl groups. However, there are still undiscovered properties of these membranes emerging from different compositions of cast solutions. Thus, it is vital to explore new membrane properties for sustainable energy generation by reverse electrodialysis (RED). In this study, the cast solution composition was easily tuned by varying the ratio of active polymer (i.e., blend ratio) and quaternary agent (i.e., excess diamine ratio) in the range of 1.07–2.00, and 1.00–4.00, respectively. The membrane synthesized with excess diamine ratio of 4.00 and blend ratio of 1.07 provided the best results in terms of ion exchange capacity, 3.47 mmol/g, with satisfactory conductive properties (area resistance: 2.4 Ω·cm², electrical conductivity: 6.44 mS/cm) and high hydrophilicity. RED tests were performed by AEMs coupled with the commercially available Neosepta CMX cation exchange membrane (CEMs). Full article

(This article belongs to the Special Issue Electrochemical Membranes: Materials, Characterization, Testing, and Cleaning)

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25 pages, 9206 KiB

Open AccessArticle

Electrodialysis Tartrate Stabilization of Wine Materials: Fouling and a New Approach to the Cleaning of Aliphatic Anion-Exchange Membranes

by Kseniia Tsygurina, Evgeniia Pasechnaya, Daria Chuprynina, Karina Melkonyan, Tatyana Rusinova, Victor Nikonenko and Natalia Pismenskaya

Membranes 2022, 12(12), 1187; https://doi.org/10.3390/membranes12121187 - 25 Nov 2022

Cited by 4 | Viewed by 3065

Abstract

Electrodialysis (ED) is an attractive method of tartrate stabilization of wine due to its rapidity and reagentlessness. At the same time, fouling of ion-exchange membranes by the components of wine materials is still an unsolved problem. The effect of ethanol, polyphenols (mainly anthocyanins [...] Read more.

Electrodialysis (ED) is an attractive method of tartrate stabilization of wine due to its rapidity and reagentlessness. At the same time, fouling of ion-exchange membranes by the components of wine materials is still an unsolved problem. The effect of ethanol, polyphenols (mainly anthocyanins and proanthocyanidins) and saccharides (fructose) on the fouling of aliphatic ion-exchange membranes CJMA-6 and CJMC-5 (manufactured by Hefei Chemjoy Polymer Materials Co. Ltd., Hefei, China) was analyzed using model solutions. It was shown that the mechanism and consequences of fouling are different in the absence of an electric field and during electrodialysis. In particular, a layer of colloidal particles is deposited on the surface of the CJMA-6 anion-exchange membrane in underlimiting current modes. Its thickness increases with increasing current density, apparently due to the implementation of a trap mechanism involving tartaric acid anions, as well as protons, which are products of water splitting and “acid dissociation”. A successful attempt was made to clean CJMA-6 in operando by pumping a water-alcohol solution of KCl through the desalination compartment and changing electric field direction. It has been established that such a cleaning process suppresses the subsequent biofouling of ion-exchange membranes. In addition, selective recovery of polyphenols with high antioxidant activity is possible. Full article

(This article belongs to the Special Issue Electrochemical Membranes: Materials, Characterization, Testing, and Cleaning)

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13 pages, 3503 KiB

Open AccessArticle

Separation and Concentration of Nitrogen and Phosphorus in a Bipolar Membrane Electrodialysis System

by Xiaoyun Wu, Wanling Cai, Yuying Fu, Yaoxing Liu, Xin Ye, Qingrong Qian and Bart Van der Bruggen

Membranes 2022, 12(11), 1116; https://doi.org/10.3390/membranes12111116 - 8 Nov 2022

Cited by 5 | Viewed by 1634

Abstract

Struvite crystallization is a successful technique for simultaneously recovering PO₄³⁻ and NH₄⁺ from wastewater. However, recovering PO₄³⁻ and NH₄⁺ from low-concentration solutions is challenging. In this study, PO₄³⁻, NH₄⁺, [...] Read more.

Struvite crystallization is a successful technique for simultaneously recovering PO₄³⁻ and NH₄⁺ from wastewater. However, recovering PO₄³⁻ and NH₄⁺ from low-concentration solutions is challenging. In this study, PO₄³⁻, NH₄⁺, and NO₃⁻ were separated and concentrated from wastewater using bipolar membrane electrodialysis, PO₄³⁻ and NH₄⁺ can then be recovered as struvite. The separation and concentration of PO₄³⁻ and NH₄⁺ are clearly impacted by current density, according to experimental findings. The extent of separation and migration rate increased with increasing current density. The chemical oxygen demand of the feedwater has no discernible impact on the separation and recovery of ions. The migration of PO₄³⁻, NH₄⁺, and NO₃⁻ fits zero-order migration kinetics. The concentrated concentration of NH₄⁺ and PO₄³⁻ reached 805 mg/L and 339 mg/L, respectively, which demonstrates that BMED is capable of effectively concentrating and separating PO₄³⁻ and NH₄⁺. Therefore, BMED can be considered as a pretreatment method for recovering PO₄³⁻ and NH₄⁺ in the form of struvite from wastewater. Full article

(This article belongs to the Special Issue Electrochemical Membranes: Materials, Characterization, Testing, and Cleaning)

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18 pages, 1513 KiB

Open AccessArticle

Use of Chitosan as Copper Binder in the Continuous Electrochemical Reduction of CO₂ to Ethylene in Alkaline Medium

by Aitor Marcos-Madrazo, Clara Casado-Coterillo, Jesús Iniesta and Angel Irabien

Membranes 2022, 12(8), 783; https://doi.org/10.3390/membranes12080783 - 15 Aug 2022

Cited by 5 | Viewed by 2953

Abstract

This work explores the potential of novel renewable materials in electrode fabrication for the electrochemical conversion of carbon dioxide (CO₂) to ethylene in alkaline media. In this regard, the use of the renewable chitosan (CS) biopolymer as ion-exchange binder of the [...] Read more.

This work explores the potential of novel renewable materials in electrode fabrication for the electrochemical conversion of carbon dioxide (CO₂) to ethylene in alkaline media. In this regard, the use of the renewable chitosan (CS) biopolymer as ion-exchange binder of the copper (Cu) electrocatalyst nanoparticles (NPs) is compared with commercial anion-exchange binders Sustainion and Fumion on the fabrication of gas diffusion electrodes (GDEs) for the electrochemical reduction of carbon dioxide (CO₂R) in an alkaline medium. They were tested in membrane electrode assemblies (MEAs), where selectivity to ethylene (C₂H₄) increased when using the Cu:CS GDE compared to the Cu:Sustainion and Cu:Fumion GDEs, respectively, with a Faradaic efficiency (FE) of 93.7% at 10 mA cm⁻² and a cell potential of −1.9 V, with a C₂H₄ production rate of 420 µmol m⁻² s⁻¹ for the Cu:CS GDE. Upon increasing current density to 90 mA cm⁻², however, the production rate of the Cu:CS GDE rose to 509 µmol/m²s but the FE dropped to 69% due to increasing hydrogen evolution reaction (HER) competition. The control of mass transport limitations by tuning up the membrane overlayer properties in membrane coated electrodes (MCE) prepared by coating a CS-based membrane over the Cu:CS GDE enhanced its selectivity to C₂H₄ to a FE of 98% at 10 mA cm⁻² with negligible competing HER. The concentration of carbon monoxide was below the experimental detection limit irrespective of the current density, with no CO₂ crossover to the anodic compartment. This study suggests there may be potential in sustainable alernatives to fossil-based or perfluorinated materials in ion-exchange membrane and electrode fabrication, which constitute a step forward towards decarbonization in the circular economy perspective. Full article

(This article belongs to the Special Issue Electrochemical Membranes: Materials, Characterization, Testing, and Cleaning)

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15 pages, 4452 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

A Study on Biofouling and Cleaning of Anion Exchange Membranes for Reverse Electrodialysis

by Gonçalo Tiago, Maria Beatriz Cristóvão, Ana Paula Marques, Rosa Huertas, Ivan Merino-Garcia, Vanessa Jorge Pereira, João Goulão Crespo and Svetlozar Velizarov

Membranes 2022, 12(7), 697; https://doi.org/10.3390/membranes12070697 - 8 Jul 2022

Cited by 9 | Viewed by 3104

Abstract

This study covers the modification, (bio)fouling characterization, use, and cleaning of commercial heterogeneous anion exchange membranes (AEMs) to evaluate their feasibility for reverse electrodialysis (RED) applications. A surface modification with poly (acrylic) acid resulted in an improved monovalent perm-selectivity (decreased sulfate membrane transport [...] Read more.

This study covers the modification, (bio)fouling characterization, use, and cleaning of commercial heterogeneous anion exchange membranes (AEMs) to evaluate their feasibility for reverse electrodialysis (RED) applications. A surface modification with poly (acrylic) acid resulted in an improved monovalent perm-selectivity (decreased sulfate membrane transport rate). Moreover, we evaluated the (bio)fouling potential of the membrane using sodium dodecyl sulfate (SDS), sodium dodecyl benzenesulfonate (SDBS), and Aeromonas hydrophila as model organic foulants and a biofoulant, respectively. A detailed characterization of the AEMs (water contact angle, ion exchange capacity (IEC), scanning electron microscopy (SEM), cyclic voltammetry (CV), and Fourier Transform Infrared (FTIR) spectra) was carried out, verifying that the presence of such foulants reduces IEC and the maximum current obtained by CV. However, only SDS and SDBS affected the contact angle values. Cleaning of the biofouled membranes using a sodium hypochlorite aqueous solution allows for (partially) recovering their initial properties. Furthermore, this work includes a fouling characterization using real surface and sea water matrixes, confirming the presence of several types of fouling microorganisms in natural streams. A lower adhesion of microorganisms (measured in terms of total bacteria counts) was observed for the modified membranes compared to the unmodified ones. Finally, we propose a cleaning strategy to mitigate biofouling in AEMs that could be easily applied in RED systems for an enhanced long-term process performance. Full article

(This article belongs to the Special Issue Electrochemical Membranes: Materials, Characterization, Testing, and Cleaning)

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12 pages, 8587 KiB

Open AccessArticle

The Application of a Modified Polyacrylonitrile Porous Membrane in Vanadium Flow Battery

by Lin Qiao, Shumin Liu, Haodong Cheng and Xiangkun Ma

Membranes 2022, 12(4), 388; https://doi.org/10.3390/membranes12040388 - 31 Mar 2022

Cited by 3 | Viewed by 2204

Abstract

Vanadium flow battery (VFB) is one of the most promising candidates for large-scale energy storage. A modified polyacrylonitrile (PAN) porous membrane is successfully applied in VFB. Herein, a simple solvent post-processing method is presented to modify PAN porous membranes prepared by the traditional [...] Read more.

Vanadium flow battery (VFB) is one of the most promising candidates for large-scale energy storage. A modified polyacrylonitrile (PAN) porous membrane is successfully applied in VFB. Herein, a simple solvent post-processing method is presented to modify PAN porous membranes prepared by the traditional nonsolvent induced phase separation (NIPS) method. In the design, polymer PAN is chosen as the membrane material owing to its low cost and high stability. The large-size pores from NIPS method are well optimized by the solvent swelling and shrinking during the solvent post-processing. Meanwhile, the interconnectivity of pores is maintained well. As a result, the ion selectivity of PAN porous membranes is dramatically improved, and the CE of a VFB with PAN porous membranes rises from 68% to 93% after the solvent post-processing process. A VFB with the modified PAN porous membranes is capable of delivering a limiting current density of 900 mA cm⁻², and a high peak power density of 650 mW cm⁻², which is very competitive among the various flow batteries. Full article

(This article belongs to the Special Issue Electrochemical Membranes: Materials, Characterization, Testing, and Cleaning)

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Review

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28 pages, 2689 KiB

Open AccessEditor’s ChoiceReview

Green Synthesis of Cation Exchange Membranes: A Review

by Stef Depuydt and Bart Van der Bruggen

Membranes 2024, 14(1), 23; https://doi.org/10.3390/membranes14010023 - 17 Jan 2024

Cited by 2 | Viewed by 4164

Abstract

Cation exchange membranes (CEMs) play a significant role in the transition to a more sustainable/green society. They are important components for applications such as water electrolysis, artificial photosynthesis, electrodialysis and fuel cells. Their synthesis, however, is far from being sustainable, affecting safety, health [...] Read more.

Cation exchange membranes (CEMs) play a significant role in the transition to a more sustainable/green society. They are important components for applications such as water electrolysis, artificial photosynthesis, electrodialysis and fuel cells. Their synthesis, however, is far from being sustainable, affecting safety, health and the environment. This review discusses and evaluates the possibilities of synthesizing CEMs that are more sustainable and green. First, the concepts of green and sustainable chemistry are discussed. Subsequently, this review discusses the fabrication of conventional perfluorinated CEMs and how they violate the green/sustainability principles, eventually leading to environmental and health incidents. Furthermore, the synthesis of green CEMs is presented by dividing the synthesis into three parts: sulfonation, material selection and solvent selection. Innovations in using gaseous SO3 or gas–liquid interfacial plasma technology can make the sulfonation process more sustainable. Regarding the selection of polymers, chitosan, cellulose, polylactic acid, alginate, carrageenan and cellulose are promising alternatives to fossil fuel-based polymers. Finally, water is the most sustainable solvent and many biopolymers are soluble in it. For other polymers, there are a limited number of studies using green solvents. Promising solvents are found back in other membrane, such as dimethyl sulfoxide, Cyrene™, Rhodiasolv^® PolarClean, TamiSolve NxG and γ-valerolactone. Full article

(This article belongs to the Special Issue Electrochemical Membranes: Materials, Characterization, Testing, and Cleaning)

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16 pages, 3257 KiB

Open AccessReview

Bipolar Membranes for Direct Borohydride Fuel Cells—A Review

by Ines Belhaj, Mónica Faria, Biljana Šljukić, Vitor Geraldes and Diogo M. F. Santos

Membranes 2023, 13(8), 730; https://doi.org/10.3390/membranes13080730 - 13 Aug 2023

Cited by 3 | Viewed by 2081

Abstract

Direct liquid fuel cells (DLFCs) operate directly on liquid fuel instead of hydrogen, as in proton-exchange membrane fuel cells. DLFCs have the advantages of higher energy densities and fewer issues with the transportation and storage of their fuels compared with compressed hydrogen and [...] Read more.

Direct liquid fuel cells (DLFCs) operate directly on liquid fuel instead of hydrogen, as in proton-exchange membrane fuel cells. DLFCs have the advantages of higher energy densities and fewer issues with the transportation and storage of their fuels compared with compressed hydrogen and are adapted to mobile applications. Among DLFCs, the direct borohydride–hydrogen peroxide fuel cell (DBPFC) is one of the most promising liquid fuel cell technologies. DBPFCs are fed sodium borohydride (NaBH₄) as the fuel and hydrogen peroxide (H₂O₂) as the oxidant. Introducing H₂O₂ as the oxidant brings further advantages to DBPFC regarding higher theoretical cell voltage (3.01 V) than typical direct borohydride fuel cells operating on oxygen (1.64 V). The present review examines different membrane types for use in borohydride fuel cells, particularly emphasizing the importance of using bipolar membranes (BPMs). The combination of a cation-exchange membrane (CEM) and anion-exchange membrane (AEM) in the structure of BPMs makes them ideal for DBPFCs. BPMs maintain the required pH gradient between the alkaline NaBH₄ anolyte and the acidic H₂O₂ catholyte, efficiently preventing the crossover of the involved species. This review highlights the vast potential application of BPMs and the need for ongoing research and development in DBPFCs. This will allow for fully realizing the significance of BPMs and their potential application, as there is still not enough published research in the field. Full article

(This article belongs to the Special Issue Electrochemical Membranes: Materials, Characterization, Testing, and Cleaning)

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