Polyelectrolyte Membranes Research Articles

Unraveling the ion transport through top and wall coated polyelectrolyte membrane pores

Polyelectrolyte-based nanofiltration membranes are obtained through a layer-by-layer sequential deposition of oppositely charged polyelectrolytes (PEs) onto a porous support structure. The resulting polyelectrolyte membrane offers tailored salt rejections for nanofiltration applications. However, little is known about the exact location of the deposited PEs on top or inside a membrane pore. Also, scarce information is available on the contribution of the different potential PE locations that affect the salt rejection of the overall membrane. Hence, research challenges, such as the influence of (a) an adsorbed PE layer inside the support membrane or (b) the bridging of the original pores and the position of the bridging layer, can only be unraveled through rigorous simulations. We present a significant extension of our previously published model into a two-dimensional modeling framework pEnPEnS (pressure p driven transport through n electrolyte layers En, n polyelectrolyte layers PEn, and the support structure S) capable of addressing the selective layer additionally formed on the walls of the support capillary structure. The model solves a set of two-dimensional nonlinear Extended Nernst-Planck-Poisson and Navier-Stokes-Brinkman equations, enabling the prediction of ionic rejections from the top coating, wall coating, and a PE bridging forming inside the capillary. The proposed model framework systematically identifies and quantifies the influence of the capillary coating beneath the top layer on NaCl rejection and addresses the challenge of improving rejection rates. The model reveals that PEs deposited inside the support structure contribute significantly to NaCl rejection. It enables the predictions of differences in the rejection rates depending on the location of the PE coating, the diameter of the support capillary, and the transmembrane pressure. The model gives insight into PE bridging forming inside the support capillary and explains how its position and fixed charge density change ion rejection rates. As such, the model unravels insightful details on the rejection characteristics of coated capillaries, making it a powerful tool for designing polyelectrolyte membranes.

Architecting side chain grafted poly (vinylidene fluoride) based graphene oxide composite polyelectrolyte membranes for hydrogen and direct methanol fuel cells

Chemically modified poly (vinylidene fluoride) (PVDF) as polyelectrolyte has generated immense interest due to its high efficiency in electrochemical energy devices. Herein, the design of a polymer electrolyte membrane (PEM) is formulated by the synergistic fusion of graphene oxide (GO) into chemically grafted PVDF with 2-acrylamido-2-methylpropane sulfonic acid (AMPS) by solution phase intercalation producing GO@PVDF-g-PAMPS composite membranes. Ozone-induced graft copolymerization technique is employed to prepare PVDF-g-PAMPS with 18.3% (w/w) degree of grafting. Incorporation of GO into the polymeric membrane generates appropriate hydrophilic-hydrophobic phase separation and constructs well-organized sub-nano slit-like pathways that elevate the proton conduction. PAG-0 membrane without any filler shows a proton conductivity (κ) of 15.1 mS/cm at 80°C whereas PAG-2 membrane (with 2% w/w GO loading) shows a κ of 25.9 mS/cm under similar conditions. The presence of a perfluorinated backbone furnishes excellent oxidative stability to the PEMs by retaining 95% of total mass and 97.3% of κ after dipping in harsh Fenton's reagent at 60°C for 6 h. Representative PAG-2 shows a peak power density of 152.9 mW/cm2 with a maximum current density of 480.6 mA/cm2 (fuel cell operating conditions: 75°C at 100% RH) in hydrogen fuel cell and a peak power density of 37.7 mW/cm2 in methanol fuel cell. Moreover, PAG-2 retains 91% of its initial OCV after 50 h of the durability test.

Weak Polyelectrolyte Membranes with a Wide Ion-Exchange Capacity (IEC) Range and Limited Water Swelling in Clean Technologies for Sustainability

Weak Polyelectrolyte Membranes with a Wide Ion-Exchange Capacity (IEC) Range and Limited Water Swelling in Clean Technologies for Sustainability

Production of boric acid by bipolar membrane electrodialysis: Evaluation of commercial and polyelectrolyte multilayers-coated ion exchange membranes

Boron is an essential element for many industrial sectors, but the European Union (EU) is entirely dependent on imports for its boron supply. To ensure a sustainable supply of boron for the EU, developing recovery strategies from secondary sources is essential. Thus, boron recovery from seawater reverse osmosis (SWRO) desalination brines using bipolar membrane electrodialysis (BMED) as part of a multi-mineral brine mining process is proposed. BMED experiments were conducted with 35 triplets of commercial membranes (100 cm2), using sodium borate solution (92.5 mM) as feed, at three different pHs (2, 9 and 12), identifying pH 12 as the best option. Moreover, commercial ion exchange membranes from PCA GmbH and Mega a.s. were coated with polyelectrolyte multilayers using layer-by-layer technique. Characterization of the coated membranes included zeta potential, contact angle, ATR-FTIR, transport number and ion exchange capacity analyses. Subsequent BMED experiments with three triplets comparing virgin and modified membranes (100 cm2), using sodium borate solution (92.5 mM) as feed, demonstrated that the coating with 4 bilayers increased the selectivity of membranes. Although the coated RALEX membranes presented the highest selectivity (7.2 for B(OH)4-/Na+ in the acid compartment), uncoated PCA membranes were the optimal choice for H3BO3 and NaOH production due to higher Na and B removal (97 %), higher concentration factors (2.5 for the acid and 4.3 for the base), and higher current efficiency for H3BO3 production (78 %).

Proton-Conducting Polyelectrolyte Membranes Containing Graphene Dots for Moisture Electric Generators

Proton-Conducting Polyelectrolyte Membranes Containing Graphene Dots for Moisture Electric Generators

Shape-Regulated Motion and Energy Conversion of Polyelectrolyte Membrane Actuators.

Smart actuators hold great potential in soft robotics and sensors, but their movement at the fluid interface is less understood and controlled, hindering their performances and applications in complicated fluids. Here an ethanol-containing polyelectrolyte actuator is prepared that demonstrates excellent actuating performance via the Marangoni effect. These actuators exhibit enduring (17min), repeatable (50 cycles), and autonomous motion on the water surface. More importantly, the motion of actuators are dependent on their shapes. Polygonal actuators with more edges exhibit round motion attached to walls of containers, while the actuators with few edges move randomly. On the basis of this property, the circular actuators can pass through pipe bends with S-shaped complex geometry. These unique advantages lend the actuators to successful applications in wireless sensing (standard 0-5V level signals) for locating obstructions inside invisible pipes and continuous energy harvesting (7700nC per cycle) for micro mechanical energy.

(Invited) PEM Water Electrolysis Stack Development and Related Characterization Tools

For decades, proton-exchange membrane (PEM) water electrolysis (WE) has been mainly used for oxygen generation in anaerobic environments. Over the past two decades, however, it has been increasingly used for hydrogen generation in the industrial sectors at various scales. The PEMWE technology is also considered a key in the ongoing energy transition, if the process of hydrogen generation by means of WE is linked to renewable energy sources, such as wind, solar, etc.The following key elements enable the operation of a PEM WE plant for hydrogen production: a PEM-based WE stack and the balance of plant. The related system includes, but not limited to such key modules as the water and oxygen management systems, hydrogen gas management system, water input system, safety system, power electronics and electrolysis cell stack power supply, control system, and some other.A WE stack comprises several cells connected in series with electrically conductive bipolar plats and end plates. General design principles for the stack involve reducing efficiency losses, while aiming at lower costs and increase in durability. WE stacks should be designed in such a way, that an even current distribution is maintained, the water feed is optimized, suitable compression ratios are achieved, and preferably high discharge pressure of hydrogen can be enabled. For the stack level, in simple terms, efficiency is benchmarked by the total applied voltage, which includes the Nernst potential, anode and cathode overpotentials, and ohmic overpotentials due to the membrane ionic resistance and interfacial resistance at given current density. Overpotential represents inefficiencies in a cell stack, and some of stack design efforts focus on reducing these overpotential contributions. However, a compromise has to be found between (a) costs reduction challenges (that are often associated with the reduction of PGM-based catalyst loading, attempts to replace Ti as a key material for the bipolar plates, and the less expensive SPE membrane), (b) sufficient durability, (c) performance of the stack, (d) increase in power density of a stack.This talk will focus on the WE stack, and its subcomponents review, as well as characterization methods for both, a single cell and a stack and also challenges of the large-scale stack manufacturing. The key components of the WE stack include ion-conductive solid polyelectrolyte membranes (SPE), anode and cathode catalyst layers (CL), bipolar plates and current collectors/ gas diffusion layers (porous transport layers).In order to gain fundamental understanding of the relationships between electrical loses, degradation of the stack components and strategies to increase power density of the stacks, advanced characterization and modelling tools need to be used. These include, but not limited to electrochemical impedance spectroscopy (EIS), current interrupt (CI), dynamic compression measurements with piezoelectric senor plates, current mapping, gas cross-over analysis, computational fluid dynamics (CFD) simulations modelling, various visualization tools, etc. For example, CFD could assist in understanding and improving fluid flow dynamics in a WE stack as it is a complex challenge that requires a detailed examination of the geometry, channel design, and operating conditions within the stack. As for EIS, the usage of the distribution of relaxation times (DRT) approach would potentially allow to focus on the direct analysis of the data rather focusing on the equivalent circuit development.Approximately 15 years ago the South African Government approved a national program HySA: Hydrogen South Africa, which resulted in the development of the expertise and capacity to conduct research, development, and earlier commercial activities around green hydrogen production by means of water electrolysis. These activities include the development of local IP at the components, stack, and system levels.

Toward highly ionic polyelectrolyte membrane: Synthesis, characterization, membrane performance and theoretical studies of PVDF-g-PAN/PAMPS hybrid membranes

Novel highly ionic polyvinylidene fluoride (PVDF) membranes grafted with an acrylonitrile monomer to yield the target (PVDF-g-PAN) via radical polymerization and then blended with the amphiphilic copolymer poly (2-acrylamido-2-methyl-1-Propane sulfonic acid (PAMPS) via physical interactions (PVDF-g-PAN)/(PAMPS), were designed and constructed. The new functional groups obtained (fluoride, nitrile, and sulfonic functions) were confirmed via FTIR analysis, and the prepared membranes were characterized using SEM, TGA, tensile strength, water contact angle, and mechanical stability instruments. The essential characteristics of the polyelectrolyte membranes, including the IEC, ionic conductivity, methanol permeability, thermal stability, and high mechanical qualities, were examined. It was discovered that, the oxidative stability of the modified membrane (P3) with a high concentration of conductive PAMPS affected the percentage of weight loss (5.25 %) at the end of 24 h. In addition, the water absorption capacity increased with increasing in the concentration of PAMPS. Similarly, the highly concentrated PAMPS modified membranes (P3) have an ionic exchange capacity and proton conductivity equal to IEC= 1.93 meq/g, which is greater than that of the Nafion membrane by 0.91 meq/g. Furthermore, appropriate DFT theoretical studies such as EHOMO, ELUMO, energy band gap and dipole moment (µ) were thoroughly examined and employed to validate the highly ionic system. It was found that, the energy band gap of PVDF-g-PAN/PAMPS was 5.19 eV, which is lower than that of the grafted polymer value (7.17 eV), confirming that the electrons are transferred readily from the HOMO level to the LUMO level. In addition, the dipole moment of the PVDF-g-PAN/PAMPS was 7.10 Debye, which is greater than the dipole moment value of the grafted polymer (2.07 Debye), indicating the highly ionic character of the hybrid polymer. Finally, the promising results obtained demonstrated favorable film-forming and structural properties, making it a promising option for polyelectrolyte membranes. It also has the added advantage of being cost-effective and can be applied in many electrochemical applications.

Chitosan/magnetic chitin nanowhisker polyelectrolyte membrane for direct methanol fuel cell applications: preparation, characterization, and performance analysis

ABSTRACT A hybrid chitosan-based nanocomposite was fabricated by chitin nanowhiskers coupled with silanized Fe3O4 nanoparticles as a polyelectrolyte membrane for direct methanol fuel cells (DMFCs). The morphological evaluations articulated that the magnetite nanoparticles were uniformly attached to the chitin nanowhiskers. After characterization of the synthesized nanowhiskers, they were incorporated into the chitosan, as a polycationic electrolyte, to investigate the performance of nanocomposite for DMFC applications. An external magnetic field was applied to the magnetic chitin nanowhiskers to induce alignment, and the effects of aligned nanowhiskers, as well as random ones, were also studied. The magnetic chitin nanowhiskers positively influenced the water uptake and proton conductivity due to the formation of hydrogen bonds between the surface functional groups of nanowhiskers and free water molecules. On the other hand, methanol permeation of the chitosan nanocomposites was reduced regarding the tortuous pathways and narrower transportation channels by the presence of nanowhiskers.

Structural and Release Properties of Combined Curcumin Controlled-Release Tablets Formulated with Chitosan/Sodium Alginate/HPMC.

Controlled-release tablets offer several benefits, such as controlled release, odor masking, ease of use, stability, extended shelf life, and reduced production costs. This study developed combined curcumin controlled-release tablets (CCCTs) to increase the bioavailability of curcumin with hydroxypropyl methylcellulose (HPMC), chitosan, and sodium alginate. The hardness of the CCCTs was 5.63-1.98 kgf, friability was 0.00-1.22%, and disintegration time was 0.00-401.25 min. Differential scanning calorimetry and Fourier-transform infrared spectroscopy indicated a high compatibility between the excipients and curcumin. CCCTs with chitosan formed a gel structure, impeded disintegration, and reduced the release rate to 72.5% in simulated gastric fluid. In simulated intestinal fluid, CCCT with the HPMC-sodium alginate group formed a polyelectrolyte membrane hydrogel to prolong release from 6 to 12 h. This study developed various CCCT formulations that can be delivered through the gastric or intestinal tracts, using chitosan and HPMC-sodium alginate as excipients, respectively. CCCT can be used as a reference strategy for controlled-release curcumin delivery in the functional and healthcare supplement development.

Development of novel proton exchange membranes based on cross-linked polyvinyl alcohol (PVA)/5-sulfosalicylic acid (SSCA) for fuel cell applications

The proton-conducting and methanol permeation behaviors of polymeric electrolyte membranes (PEMs), as well as the expensive nature of direct methanol fuel cell (DMFC) components, pose major concerns in DMFC performance and commercialization. As a result, this research aimed to develop low-cost polyelectrolyte membranes based on cross-linked poly(vinyl alcohol)/5-sulfosalicylic acid dehydrate (PVA/SSCA) composite. Chemical cross-linkers and modifiers offer the essential chemical and mechanical stability of the developed membranes for usage as polyelectrolyte membranes (PEMs). The manufactured composite proton exchange membranes provide several benefits, including significant thermal, chemical, and mechanical stability. The results revealed that extending the SSCA molar concentration increased IEC outcomes of the synthesized membranes, reaching an elevated level of (3.31 meq g−1) compared to (0.91 meq g−1) for the Nafion 117 membrane. The proton conductivity of a composite membrane (102 μm thick) measured by impedance spectroscopy was relatively (0.078 S cm−1) and found comparable to other PVA-based composite membranes reported in the literature. Other key parameters, such as methanol permeability, were measured for constructed composite proton exchange membranes (2.52 × 10–7 cm2 s−1), which were much lower than Nafion 117 (3.39 × 10–6 cm2 s−1). The Fourier transform infrared (FT-IR), Raman scattering spectroscopy, scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) spectroscopy, elemental analysis, and thermal gravimetric analysis (TGA) were among the techniques used to characterize the synthesized membranes. These characterizations confirm the structural interaction between the membrane components’ crystalline nature, and no signs of phase separation or cracks were found; surface morphology and good membrane homogeneity, elemental analysis, and the membranes’ thermal stability (up to 290 °C). The membranes were also mechanically characterized using a universal testing machine (UTM), which revealed good mechanical stability. The findings demonstrate that a low-cost proton exchange membrane could potentially be synthesized for DMFC applications.

Metal-organic framework integrated surface-engineered polyelectrolyte membranes enhancing tetrahydrofuran dehydration

BackgroundEnhancing composite membrane performance is crucial for industrial separation processes. Integrating metal-organic frameworks (MOFs) into membranes offers a promising strategy. We introduce a novel approach by integrating HKUST-1 MOF within a polyelectrolyte matrix to improve membrane efficiency. MethodsA layer-by-layer self-assembly technique on a hydrolyzed polyacrylonitrile support integrates HKUST-1 into a polyelectrolyte matrix. Polyethyleneimine (PEI) and polyacrylic acid (PAA) form the polyelectrolyte layer through electrostatic interactions. The incorporation of HKUST-1 within the PEI matrix enhances separation efficiency, particularly in tetrahydrofuran dehydration, with optimal conditions using 100 ppm of HKUST-1 and forming 2 bilayers. Significant findingsUnder optimal conditions, the resulting membrane exhibits exceptional performance. It demonstrates a permeation flux of 1442.30 g∙m−2∙h−1, a water concentration in the permeate of 98.0 wt%, and a separation factor of 440. The modified membrane also shows remarkable stability across varying temperatures (25–55 °C) and tetrahydrofuran concentrations in the feed (10–90 wt%) during long-term testing. These findings highlight the membrane's potential for enhancing separation processes in the chemical industry.

Enhanced ethanol dehydration performance of cationic COFs filled anionic alginate hybrid membranes

Adding charged fillers to incorporate long-range electrostatic interactions is an effective way to reduce structure defects and improve separation performance of polyelectrolyte membranes. In this study, three cationic covalent organic frameworks (COFs), TpEB, TpTGCl, and TpPy, were incorporated into anionic alginate to prepare hybrid membranes for pervaporation dehydration of ethanol. With the increase of electrostatic interaction, the decrease in the mobility of polymer chains leads to an increase in the crystallinity and selectivity. Meanwhile, the inherent hydrophilic channels of iCOFs provided additional mass transfer channels, increasing the membrane permeability. When separating a 90 wt% ethanol/water mixture at 76 °C, the hybrid membrane containing 15 wt% TpEB exhibited the highest separation performance with a permeation flux of 2460 g m-2 h-1 and a separation factor of 2110, and it also demonstrated ideal long-term stability. This work provides a new perspective for the selection of fillers in the design process of hybrid membranes in the future.

Development and Utilization of Polyelectrolyte Membranes Based on Biomass and Agricultural Waste

Development and Utilization of Polyelectrolyte Membranes Based on Biomass and Agricultural Waste

Functionally antagonistic polyelectrolyte for electro-ionic soft actuator

Electro-active ionic soft actuators have been intensively investigated as an artificial muscle for soft robotics due to their large bending deformations at low voltages, small electric power consumption, superior energy density, high safety and biomimetic self-sensing actuation. However, their slow responses, poor durability and low bandwidth, mainly resulting from improper distribution of ionic conducting phase in polyelectrolyte membranes, hinder practical applications to real fields. We report a procedure to synthesize efficient polyelectrolyte membranes that have continuous conducting network suitable for electro-ionic artificial muscles. This functionally antagonistic solvent procedure makes amphiphilic Nafion molecules to assemble into micelles with ionic surfaces enclosing non-conducting cores. Especially, the ionic surfaces of these micelles combine together during casting process and form a continuous ionic conducting phase needed for high ionic conductivity, which boosts the performance of electro-ionic soft actuators by 10-time faster response and 36-time higher bending displacement. Furthermore, the developed muscle shows exceptional durability over 40 days under continuous actuation and broad bandwidth below 10 Hz, and is successfully applied to demonstrate an inchworm-mimetic soft robot and a kinetic tensegrity system.

Interfacial analysis of the ion-transport process controlling the steady-state current in a two-phase electrodeposition system using polyelectrolyte membranes

An interfacial model has been developed for describing ion transport kinetics at the membrane/solution interface in the new solid-electrodeposition system.

Solid-state electrochemical oxidation with polyelectrolyte membrane stamps for micro-/nanoscale pattern formation on Au surfaces.

Nanoscale-patterned Au surfaces are promising for a wide range of applications from bio/chemical sensors to high-performance electrodes. However, pattern formation using conventional resist-based methods is complex, expensive, and environmentally unfriendly. Herein, we report a novel approach for pattern formation on Au surfaces using solid-state electrochemical treatment with polymer electrolyte membrane (PEM) stamps. During electrolysis, the patterned structure of the PEM stamp was transferred onto the Au surface to form micro- and nanoscale oxide patterns. X-ray analysis of the treated surface confirmed the formation of an oxide film on the Au surface, which was subsequently reduced to metallic Au after air exposure for several weeks. Although the pattern height decreased with air exposure, a patterned structure with a height of several hundred nanometers was maintained following oxide reduction. Reflectance spectroscopy revealed that the patterned Au surface exhibited sharp reflectance peaks, the intensities and positions of which strongly depended on the measurement angle, which are key characteristics of diffraction gratings. This fast and facile electrochemical treatment process is promising for the preparation of patterned Au surfaces that can be applied in optical gratings and localized surface plasmon resonance sensors.

Design of sulfonated polystyrene grafted cellulose acetate membrane for direct methanol fuel cells

Novel low-temperature proton conducting membranes are fabricated from commercial and low-cost cellulose acetate (CA). Rather than a normal modification procedure, sodium 4-styrene sulfonate groups (SSA) are grafted into cellulose acetate chains through a facile one-step free radical polymerization. The resulting CA@P(SSA) membranes with different monomer concentrations were characterized using advanced and relevant techniques such as FT-IR, TGA, and SEM. The grafting of side-chain groups was adjusted to maximise the physicochemical features of the fabricated membranes, such as ion exchange capacity, water and methanol absorption, and conductivity. By considering these features the optimized membrane (Corresponding to 1.5 wt% SSA) exhibits excellent thermal-oxidative stability and tensile strength (22.742 N) better than Nafion® 212 (16.153 N). In addition, the grafted membrane demonstrated lower methanol permeability (5.514×10−7cm2/s)andenhanced ionic conductivity (4.77×10−3S/cm) with membrane selectivity of 8.65×103S.s/cm3 with peak power density (24.6 mW/cm2). In addition, the optimized membrane showed increase in performance than pristine CA membrane. Thus, these results provide new, straightforward, high-performance and low-cost polyelectrolyte membrane with a significant potential for direct methanol fuel cell.

An “organic-inorganic” hybrid multilayer film for comprehensive support in soft and hard tissue regeneration after osteosarcoma resection

Three major complications often occur after osteosarcoma resection: large bone defects, infectious wounds, and tumor recurrence. In addition to conventional internal fixation and auto- or allografts, multifunctional supportive treatments are needed for limb reconstruction after tumor removal. With inspiration from the "organic-inorganic" hybrid concept, we developed a freestanding polyelectrolyte membrane (PEM) using a layer-by-layer (LBL) deposition of quaternized chitosan (QCS) and hyaluronic acid (HA), and with copper-doped laponite (CuLAP) intercalation. The CuLAP demonstrated photothermal conversion capabilities under near-infrared (NIR) light irradiation, and displayed glutathione (GSH)-depleted Fenton-like catalytic activity. The further engineered PEM possesses a "brick and mortar" structure with enhanced surface roughness and stiffness. The fusion of CuLAP-mediated GSH-depleted chemodynamic treatment (CDT) and moderate photothermal therapy (PTT) facilitated tumor ablation and bactericidal effects. Moreover, the continuous release of copper ions and silicates aided angiogenesis and osteogenesis, supporting the regeneration of both soft (skin) and hard (bone) tissues. This all-in-one platform offers a promising clinical tool for assisting tissue reconstruction after osteosarcoma resection.

Amphoteric polyelectrolyte ultrafiltration membranes with high permeability property via in-situ modified by PES-N and PES-COOH

Ultrafiltration membrane is one of the most commonly used separation materials for wastewater treatment, due to its low operating pressure, high flux and large specific surface area. In this work, we utilized PES polymer as a polymer precursor to prepare a series of amphoteric polyelectrolyte membrane with different content of amphoteric polyelectrolyte group via simple polymer blending processes. The amphoteric polyelectrolyte groups in amphoteric polyelectrolyte membrane could effectively regulate the retention ability and significantly improve the water flux of membrane. The amphoteric polyelectrolyte membrane with the content ratio of 4:6 (PES-N/PES-COOH) exhibited the highest water flux of 467 Lm−2 h−1 and BSA retention factor of 94.2% than that of other ultrafiltration membranes owning to the abundant porosity and suitable thickness of the top layer. Moreover, the results of static BSA adsorption and flux recovery ratio also proved that the amphoteric polyelectrolyte membrane have a good BSA rejection and antifouling performance. Therefore, these results reveal a simple synthesis and design strategy for constructing the high-performance amphoteric polyelectrolyte membrane for water treatment and provide theoretical and technical guidance for water treatment process based on membrane technology.