Ion-exchange Membranes Research Articles

Electrodeposition modification of heterogeneous cation exchange membrane using expanded polystyrene waste: Enhanced electrochemical properties and electrodialytic performance

In this study, surface modification of a cation exchange membrane based on polyvinyl chloride was accomplished via electrochemical deposition of post-sulfonated waste-expanded polystyrene aiming to enhance its electrochemical properties and electrodialytic performance. The membrane was synthesized by the phase inversion method, modified with different concentrations of polyelectrolyte, characterized by FTIR and SEM analyses, and applied for electrodialytic desalination of NaCl solution. Deposition of sulfonated polystyrene with polyelectrolyte concentration of 2 g/l, current of 8 mA/cm2, and period time of 30 min caused a reduction in electrical resistance up to 52 %. Furthermore, the sodium ionic flux through electrodialytic desalination was improved by 58 % as a result of the promotion of the electrochemical properties of the membrane.

Crossover Flux and Ionic Resistance Metrics in Polysulfide-Permanganate Redox Flow Battery Membranes

A survey of 23 commercially available cation exchange membranes was performed for the downselection of membranes for use in a polysulfide-permanganate redox flow battery (pS-Mn RFB). The survey measured the flux of permanganate ions across a 0.1 mol L−1 concentration gradient as well as the membrane resistance in a 0.5 mol L−1 sodium chloride solution. The membranes exhibited the characteristic flux/resistance trade-off observed in most classes of membranes. To connect the individual membrane testing to how the membranes will perform in a device, cell performance data in a pS-Mn RFB was collected for three membranes from the survey. The coulombic, voltaic, and energy efficiency at low cycle counts aligned with the predictions from the membrane flux and resistance survey results. The study also identified three membranes—Fumapem F-930-RFS, Fumapem FS-715-RFS, and Aquivion E98-09S—that outperformed most other membranes regarding their position on the flux-resistance trade-off curve, indicating them to be good candidates for further testing.

Unexpected Behavior of Streaming Potential in Ion-Exchange Membranes.

Streaming potential is one of the numerous electrokinetic phenomena created when an electrolyte flows along a charged surface. In membranes, applying the charged cylindrical pore model, streaming potential can be used to estimate, e.g., the pore size and the charge density of such pores. In this study, we are extending streaming potential experiments to ion-exchange membranes (IEMs) and trying to verify the existing models with the measurements. According to the Donnan equilibrium between an electrolyte solution and an IEM, the solution concentration should not affect the streaming potential if the membrane charge is even moderately low. Yet, the streaming potential varied substantially with the solution concentration, as in the case of nearly neutral porous membranes. In addition, the existing theory does not include the membrane thickness, but we found that thinner membranes showed larger streaming potentials. These dilemmas are discussed in this paper.

Constructing ionic highway in capacitive deionization via integrated electrodes based on bifunctional ionomer

In this work, bifunctional ionomeric capacitive deionization (BICDI) electrode are constructed by using bifunctional ionomer as electrode binder and ion exchange material for the enhancement of desalination performance. Compared with traditional membrane capacitive deionization (MCDI) electrodes, the BICDI electrodes were fabricated by using the poly(arylene alkylene) based ionomer to substitute the PVDF binder and ion exchange membrane (IEM). The BICDI electrode based on bifunctional ionomer exhibits higher hydrophilicity, special ion exchange capability, as well as excellent electrochemical properties in comparsion with that of MCDI electrode counterpart. The built-in ionic groups in poly(arylene alkylene) based ionomers could create interconnected ionic highway between different electrode particles, which encourages effective ion transport. The desalination results validated that the salt adsorption capacity (SAC) of carbon-based BICDI electrodes reached 19.2 mg g−1, which is 2.2 times that of MCDI electrodes during adsorption-desorption cycles. Meanwhile, BICDI electrode possesses exceptional charge efficiency (96.6 %), which is much higher than that of MCDI (76.8 %). In the case of BICDI device, the ionomer utilization rate increased by a factor of 88 compared to that of ion exchange membrane in MCDI device. Especially, the economic cost of the integrated BICDI electrodes module is only $35 m−2, which is much cheaper than that in conventional MCDI system ($520 m−2). It is reasonable to believe that the integrated BICDI electrode incorporated with charged bifunctional ionomer proposed in this work provide novel insights and strategies for the high-performance and large-scale CDI applications.

Facile surface modification of cation exchange membranes via Debus-Radziszewski in-situ cross-linking for lithium extraction from salt-lakes

Lithium extraction from salt-lakes is a crucial way to solve the global shortage of lithium resources. With high sustainability and efficient ion separation, electrodialysis (ED) has a high potential for lithium extraction from salt-lakes, yet suffering from the challenges of cation-cation selectivity. In this work, a facile Debus-Radziszewski in-situ cross-linking approach was proposed to construct a polyethyleneimine modification layer containing imidazole groups (PEI-Im) on a common cation exchange membrane (commercial membrane, i.e., CTG membrane) surface to enhance the lithium selectivity. The pore size, architecture rigidity and charged characteristic of this PEI-Im layer were controlled via adjusting the reaction conditions. The resultant membrane (PEI-Im-CTG) exhibited high Li+ permeation rate (0.89 mol·m−2·h−1) and excellent Li+/Mg2+ permselectivity (13.1), which are 4.0 times and 19.8 times higher than that of the pristine CTG membrane, respectively. Moreover, the PEI-Im-CTG membrane based two-stage ED process showed a high Li+ purity (∼99.90 %) and low energy consumption (∼0.158 kWh·mol-1Li+) for Li+ extraction from simulated salt-lakes. This work offers a facile and effective strategy for membrane modification with high Li+ selectivity, which is promising in lithium extraction from salt-lakes.

On the electrokinetic remediation of Pb-contaminated soil: A coupled electro-transport-reaction modelling study based on chemical reaction kinetics

The accumulation of lead (Pb) in soil resulted from industrialization and urbanization poses a threat to human health and the ecosystem. This study proposes a mathematical model for Pb migration and transformation in soil porous media, aiming to guide the design of electrokinetic remediation schemes for Pb-contaminated soils. To improve the validity of the model, the chemical reactions considered in the model are all based on chemical reaction kinetics, which were usually overlooked for model simplification. The model quantitatively describes various physical and chemical processes of Pb at the soil-pore fluid interface and in the pore fluid, including diffusion, electromigration, electroosmosis, electrolytic water reaction, precipitation, adsorption/desorption, protonation/deprotonation reaction, and water self-ionization reaction. The numerical results show that the pH value is a key factor affecting the distribution of Pb in the soil and determining the removal efficiency of Pb. The effects of different enhancement methods on Pb concentration distribution and removal efficiency were evaluated with this model. It was found that placing a cation exchange membrane at the cathode boundary while using 0.01 M nitric acid as anode electrolyte can effectively improve Pb removal efficiency from 3.9% to 93.6%. The developed model can be used to guide the design of the enhanced electrokinetic remediation schemes.

Short-chain carboxylate continuous production from food waste with in situ extraction: Novel design to reduce chemical input for pH control and alleviate membrane fouling

The production of short-chain carboxylates (SCCs) from readily degradable food waste exhibits superior product value compared to biogas production, but SCCs’ high solubility poses challenges in their production and recovery. In this study, we applied two novel modules to in-situ extract SCCs from the continuously produced fermentative broth, namely direct coupling of bipolar membrane electrodialysis (BPED) and the integration of upstream membrane permeation (MP) and BPED. The remarkable extraction efficiency of BPED effectively mitigated the inhibitory effects from the accumulation of SCCs products, yielding 475.2 mg gVS−1, which was 20.26% higher than the control phase. The OH− generated by the bipolar membrane was cycled back to regulate the pH of bioreactor, thereby completely eliminating the need for external alkaline additives. The upstream MP effectively prevented ion exchange membrane fouling, and the OH− generated by BPED achieved the in-situ regeneration of MP’s alkali extract, reducing the OH− demand by 40% in MP+BPED stage. It was also observed that BPED exhibited higher selectivity towards small-molecule acetic acid, while MP tended to recover larger-molecule caproic acid. Selective extraction of specific SCC drove the product spectrum of the bioreactor to produce more SCC that was selectively extracted.

A hybrid electrochemical system for spontaneous green‑hydrogen production with simultaneous desalination using catechol oxidation

Green hydrogen, commonly produced through water electrolysis, has attracted considerable attention owing to its energy-efficient and eco-friendly properties. However, since conventional water electrolysis system has fatal drawbacks owing to the high process cost and energy requirements, various approaches are being adopted to increase its energy efficiency. In this study, a novel hybrid system for green hydrogen production was designed by replacing the oxygen evolution reaction (OER) with electrochemical oxidation of catechol (CAT). CAT is an environmental pollutant generated by diverse industries and needs to be further treated because of its toxicity to humans and nature. Accordingly, to facilitate the degradation of CAT and increase the energy efficiency, the pH values of the anolyte (containing CAT) and catholyte were adjusted to alkali and acid, respectively. Two types of ion-exchange membranes (IEMs; anion-/cation-exchange membranes) were coupled to divide the hybrid cell into three compartments, and a buffer solution (NaCl solution) was injected between the IEMs. As a result, the hybrid system output 3.75 mW/cm2 of electricity, spontaneously produced hydrogen with 4.2 mL/h of hydrogen production rate and removed ions from the buffer solution with 0.46 mg/cm2∙min of high desalination rate.

Harnessing the Intrinsic Ionic Rectification Properties of Blind‐Hole Nanoporous Anodic Alumina for Osmotic Energy Generation

AbstractThe full potential of blue energy as a sustainable technology for high‐performance energy generation remains elusive. Nanoporous anodic alumina (NAA) is extensively used as a passive structural support to develop a broad variety of ion exchange membranes based on other materials for osmosis‐driven energy generation. However, the intrinsic ionic current rectification (ICR) properties of the inherited hemispherical barrier oxide layer (BOL) closing the bottom tips of NAA's nanopores are overlooked. As‐produced NAA provides new avenues to control ionic transport through its BOL, acting as an ICR model system to study electric current associated with the selective flow of ions across anodic oxides. This study explores the intrinsic capability of NAA membranes for osmotic energy generation. NAA membranes with a working area of 13.4 mm2 can generate a power density yield of ≈2.8×10−4 W m−2 when subjected to a 105‐fold salinity ratio at a pH 3 in CaCl2 electrolyte, achieving a high efficiency of 7%. With better understanding of the mechanism of ion transport on osmotic generation, the intrinsic properties of NAA membranes can be tailor‐engineered to maximize blue energy yield, paving the way for future developments in a scalable technology suited for real‐life applications.

Electrodialysis of moderately concentrated solutions: Experiment and modeling based on a simplified characterization of ion-exchange membranes

Electrodialysis (ED) is a cost-effective and environmentally friendly process; it is considered a key step in Zero Liquid Discharge systems. However, the ED process producing a fairly concentrated solution is not well understood. An ED process where 10 L of 0.5 M NaCl was circulated in diluate stream (DS) and 0.1 L of initially 2.0 M NaCl circulated in concentrate stream (CS) was studied. The concentration of concentrate increased up to 3.5 M. The electrodialyzer's design eliminated current leakage. Ion-exchange membranes, MK-40, MA-41 (Shchekinoazot) and CJMA-3 (Chemjoy Polymer Materials), were characterized prior to ED. Based on the concentration dependences of membrane conductivity and diffusion permeability, the “true” (ti⁎) ion transport numbers in the membranes were found; the water transport number (tw) was found from volumetric measurements. It was shown that the current efficiency, η, found using ti⁎ is quantitatively consistent with η found in the ED experiments. To calculate the time dependences of solution concentration and volume in CS, a mathematical model was built. For the first time, ti⁎ and tw determined in independent experiments, were used as parameters. The only fitting parameter was the osmotic permeability coefficient. A good agreement with experimental results is obtained.

Fabrication of pore-filling cation-exchange membrane from waste polystyrene and Spunbond Meltblown Spunbond (SMS) non-woven polypropylene fabric as the substrate

Commercial ion-exchange membranes are typically thick, possessing limited mechanical strength, and have relatively high fabrication costs. In this study, we utilize a three-layer polypropylene fabric known as Spunbond Meltblown Spunbond (SMS) as the substrate. This choice ensures that the resulting membrane exhibits high strength and low thickness. SMS substrates with various area densities, including 14.5, 15, 17, 20, 25, and 30 g/m2, were coated with different concentrations of waste polystyrene solution (ranging from 5 × 104 to 9 × 104 mg/l) before undergoing sulfonation using concentrated sulfuric acid. The physicochemical and mechanical properties of the membrane were characterized and compared with those of commercial Neosepta CMX and Nafion-117 cation-exchange membranes. Remarkably, the fabricated membrane exhibited good performance compared to commercial ones. The cation-exchange capacity (2.76 meq/g) and tensile strength (37.15 MPa) were higher, and the electrical resistance (3.603Ω) and the thickness (130 μm) were lower than the commercial membranes.

A Comparative Study on the Removal of Fluorides from Groundwater: Strategies and Technologies

This study conducts a comprehensive comparative analysis of various strategies and technologies employed for the removal of fluorides from groundwater, addressing the increasing concern over elevated fluoride levels in water sources. High fluoride concentrations pose significant health risks, including dental and skeletal fluorosis, necessitating effective and sustainable removal methods. The research evaluates the efficiency, cost-effectiveness, and environmental impact of different fluoride removal techniques, providing valuable insights for water treatment practitioners, policymakers, and communities grappling with fluoride-contaminated groundwater. The study begins by outlining the prevalence of fluoride contamination in groundwater and the associated health risks, establishing the critical need for reliable removal methods. Subsequently, a review of existing literature presents an overview of conventional and emerging technologies utilized for fluoride removal. Conventional methods such as coagulation, precipitation, and adsorption are examined, considering their efficiency, operational ease, and cost implications. The study then delves into advanced technologies like membrane processes, ion exchange, and electrochemical methods, assessing their applicability and effectiveness in diverse groundwater contexts. Environmental sustainability is a key focus throughout the analysis, with a critical examination of the by-products and waste generated by each removal method. The ecological footprint, including energy consumption and material usage, is considered to provide a holistic understanding of the environmental impact associated with fluoride removal technologies. Furthermore, the economic feasibility of each method is evaluated, considering capital and operational costs. Comparative cost analyses offer insights into the affordability and scalability of different removal technologies, aiding decision-makers in selecting suitable methods based on financial constraints. The study concludes with a synthesized overview of the comparative analysis, emphasizing the strengths and limitations of each fluoride removal method. In summary, this comparative study contributes to the broader understanding of fluoride removal technologies, facilitating informed decision-making in addressing groundwater contamination. The findings are anticipated to inform researchers, water treatment professionals, and policymakers, guiding the selection of appropriate and context-specific fluoride removal methods to ensure safe and potable groundwater sources

Carbon black-coated SPEEK membrane for efficient vanadium flow batteries

Ion exchange membrane is a key component of vanadium flow batteries (VFB). Development of low-cost and high ion selectivity membrane is essential to promote practical application of VFB. Here we report a kind of carbon-coated membrane by spraying coating Super P/polyvinylidene fluoride slurries on the surface of sulfonated poly(ether ether ketone) membrane (SPEEK/SP@PVDF). The SP attached to the membrane surface or infiltrated into the membrane matrix can synergistically promote the transport of protons while inhibiting the penetration of vanadium ions. In addition, the surface SP@PVDF layer can effectively shield the strong oxidizing VO2+ in the posolyte. As a result, the VFB with the optimized SPEEK/SP@PVDF membrane demonstrates a stable energy efficiency of >80 % at 200 mA cm−2 and a peak power density of 1073.79 mW cm−2 at 1300 mA cm−2, indicating the great potential of this carbon black-coated membrane for potential application in VFB.

Modelling of selective ion partitioning between ion-exchange membranes and highly concentrated multi-ionic brines

In recent years, the growing interest in the use of Ion-Exchange Membranes, in the treatment of highly concentrated multi-ionic brines for the selective recovery of critical elements, has prompted the research of fundamental models capable of predicting the IEMs selectivity towards like-charged species. Prior studies have proposed ion partitioning models limited to single-salt solutions that were validated only up to moderate salt concentrations. In this work, we developed a novel multi-ionic extension of the Manning counter-ion condensation model, aiming to predict the sorption selectivity of like-charged counter-ions. Furthermore, the peNRTL model was coupled with the extended Manning model to broaden its applicability range, encompassing membrane equilibrated with very highly concentrated solutions. Novel experimental ion sorption tests with single-salt and binary solutions including NaCl, KCl, MgCl2, and CaCl2 at high concentrations were performed with the commercial cation-exchange membrane Fumasep FKE-50. To the best of Authors’ knowledge, the proposed model for the first time successfully provided quantitative predictions of multi-ionic ion partitioning for all the systems investigated up to extremely high external salt concentrations. The outcomes of this work suggest a strong influence of the local non-electrostatic interactions on the activity coefficients in the membrane phase at high external concentration and highlight the key role of counter-ions hydration state in the condensation phenomenon.

A Low-Carbon Optimal Operation Method for an Industrial Park Multi-Energy Coupling System Utilizing By-Product Hydrogen

To enhance the utilization efficiency of by-product hydrogen and decrease the power supply expenses of industrial parks, local utilization of by-product hydrogen plays a crucial role. However, the methods of utilizing by-product hydrogen in industrial parks are relatively limited. In response to this issue, an optimization method for a multi-energy system with by-product hydrogen considering the production process of chlor-alkali plants was proposed in this paper. Firstly, on the source side, models were established for hydrogen production using the ion exchange membrane electrolyzer and for the energy consumption during the caustic soda solution evaporation process. Secondly, on the load side, this paper explored the potential for local utilization of by-product hydrogen, including its participation in the production of downstream chemical products, combustion when mixed with natural gas, and utilization in hydrogen fuel cells. Next, this paper considered the influence of correlations among various loads within the factory and wind power generation, proposing a method for generating scenarios that takes into account the spatiotemporal correlation of source-load variables. Then, aiming to minimize the system operation cost and carbon trading cost, an operation strategy for a multi-energy system in a low-carbon industrial park, considering local utilization of by-product hydrogen, was proposed. Finally, the effectiveness of the scenario generation method proposed in this paper, considering spatiotemporal correlation, and the economic and environmental benefits of the proposed operation model utilizing the by-product hydrogen are verified through arithmetic simulation, based on the operation data of a chlor-alkali chemical park.

Ion migration mechanism of electrochemical water softening in dual-chamber reactors and their performance for real circulating cooling water

Electrochemical water softening studies often use ion exchange membrane (IEM) reactors. However, their practical application is limited because of inevitable cathodic scaling. To overcome this challenge, one necessary approach is to understand the ion migration mechanism in the typical IEM reactor. In this study, we used operando visualization to reveal that the divider such as IEM or nylon nets was essential to confine the neutralization reaction between H+ and OH−. Ca2+ and Mg2+ may transfer from the anode chamber through the divider into the cathode chamber via electromigration. Using mesh electrodes instead of plate electrodes, the total hardness removal in the cathode chamber and anode chamber was 94.2% and 92.5%, respectively. The high removal rate was attributed to H2 microbubbles produced by cathodic water electrolysis, which drove OH− ions diffusion into solution and sequentially strengthened the nucleation of scale crystals in solution rather than on the cathode surface. On the basis of the above ion migration mechanism, the revolutionized reactor with mesh electrode module and nylon-net divider exhibited good performance in softening real circulating cooling water, and the total hardness removal exceeded 93.1% during 30 h running. These results open new horizons for improving the practicability of electrochemical water softening.

Electrodialysis for efficient antisolvent recovery in precipitation of critical metals and lithium-ion battery recycling

It has proven effective to recover metal compounds from aqueous mixtures by use of antisolvents; organic compounds that induce selective precipitation. A challenge with antisolvents is that they are both costly to produce and recover on an industrial scale. In recycling of lithium-ion batteries and recovering critical metals, we find that electrodialysis can be a competitive method for purifying and recycling antisolvents. In this study we investigate the use of electrodialysis to separate salt and water from a ternary solution of water, KCl and ethanol. A coupled non-equilibrium electrochemical model is developed to understand how such systems may be operated, designed, and which characteristics that are required for the ion exchange membranes. We demonstrate how the water transference coefficients of the membranes should be tuned in the process optimisation and why membrane property design is crucial to the success of this concept. Residual mixtures from antisolvent precipitation, with ethanol (EtOH) solvent weight fractions around 0.6-0.7, can be demineralised and the EtOH fraction increased by 0.1-0.2 at an energy requirement of 60-200 kWh mEtOH−3 by use of electrodialysis. In an example application of the concept, aqueous KCl is precipitated by recycled ethanol in a cyclic process, requiring 0.161 kWh molKCl−1. This example case considers complete ethanol rejection by the membranes and abundant water co-transport, characterised by the transference coefficients: tw=15 and ta=0 for water and EtOH respectively. The findings pave the way for new applications with aqueous mixtures of critical metals.

Anion exchange membranes with orderly channels enabled by charge transfer interactions for fast transportation of Cl−

The formation of an ordered microphase separation structure and the realization of efficient selective ion conduction by precise regulation of the self-assembly process of solid ionic conductive polymers are important in the fields of batteries and electrodialysis. To prepare ion exchange membranes with high conductivity and selectivity, we report a strategy for the design of a selective directional self-assembly backbone by the introduction of charge transfer interactions. Fluorescence spectroscopy (FL) and nano-scale microscopy analysis confirmed the self-assembly of the backbone with charge transfer interactions which resulted in good microphase separation structures for fast transportation of Cl−. The obtained QP(NDIB/PyB)-1 anion exchange membrane (AEM) showed the highest chloride ion conductivity of 83 mS cm−1 (80 °C). In addition, the selectivity of QP(NDIB/PyB)-X was verified by separation experiments of Cl− and SO42‐ (PSO42‐Cl‐ = 21.8). This introduction of electron transfer interactions into polymer structures is expected to contribute to the expansion of ion channel construction strategies and the development of ion-exchange membranes.

Performance Study on Brackish Water Desalination Efficiency Based on a Novel Coupled Electrodialysis–Reverse Osmosis (EDRO) System

Reverse osmosis (RO) is a commonly used desalination technology, but due to high requirements concerning the quality of the feed water, there still exists permeate flux related to the operating conditions, and the solute removal rate is low. Electric fields have a facilitating effect on RO desalination performance. Previous studies have focused on investigating the combination of RO and electrodialysis (ED) processes separately, without directly exploiting their interactions. To address this issue, this study proposes a novel coupling device that combines both RO and ED technologies in a single unit and investigates their mutual enhancement effects on brackish water desalination. The results show that the coupled EDRO system can mutually enhance the performance of RO and ED processes. The permeate flux ratio of the RO membrane increased with increasing voltage, reaching a maximum value of 23.7% at a feed concentration of 10,000 mg/L. The solute rejection by the ion-exchange membrane also increased with increasing pressure, reaching a maximum value of 14.95% at the same feed concentration. In addition, the specific energy consumption of the coupled system was also reduced compared to a standalone operation, with maximum reductions of 9.5% and 19.2% for RO and 2.5% and 3.4% for ED at 5000 and 10,000 mg/L feed concentrations, respectively.

Ultra-Thin Ion Exchange Membranes by Low Ionomer Blending for Energy Harvesting.

Exploring the utilization of ion exchange membranes (IEMs) in salinity gradient energy harvesting, a technique that capitalizes on the salinity difference between seawater and freshwater to generate electricity, this study focuses on optimizing PVDF to Nafion ratios to create ultra-thin membranes. Specifically, our investigation aligns with applications such as reverse electrodialysis (RED), where IEMs facilitate selective ion transport across salinity gradients. We demonstrate that membranes with reduced Nafion content, particularly the 50:50 PVDF:Nafion blend, retain high permselectivity comparable to those with higher Nafion content. This challenges traditional understandings of membrane design, highlighting a balance between thinness and durability for energy efficiency. Voltage-current analyses reveal that, despite lower conductivity, the 50:50 blend shows superior short-circuit current density under salinity gradient conditions. This is attributed to effective ion diffusion facilitated by the blend's unique microstructure. These findings suggest that blended membranes are not only cost-effective but also exhibit enhanced performance for energy harvesting, making them promising candidates for sustainable energy solutions. Furthermore, these findings will pave the way for advances in membrane technology, offering new insights into the design and application of ion exchange membranes in renewable energy.