Commercial Ion Exchange Membranes Research Articles

Performance of Reverse Electrodialysis System for Salinity Gradient Energy Generation by Using a Commercial Ion Exchange Membrane Pair with Homogeneous Bulk Structure

Salinity gradient energy is a prominent alternative and maintainable energy source, which has considerable potential. Reverse electrodialysis (RED) is one of the most widely studied methods to extract this energy. Despite the considerable progress in research, optimization of RED process is still ongoing. In this study, effects of the number of membrane pairs, ratio of salinity gradient and feed velocity on power generation via the reverse electrodialysis (RED) system were investigated by using Fujifilm cation exchange membrane (CEM Type 2) and FujiFilm anion exchange membrane (AEM Type 2) ion exchange membranes. In the literature, there is no previous study based on a RED system equipped with Fujifilm AEM Type II and CEM Type II membranes that have homogeneous bulk structure. Using 400 µm of intermembrane distance, maximum obtainable power density by 5 pairs of Fujifilm membranes at 1:45 salinity ratio and with a linear flow rate of 0.833 cm/s was 0.426 W/m2.

High-Efficient Nanocomposite Ion Exchange Membranes for Lithium Polysulfide (Li-PS) Redox Flow Battery (RFB)

Redox flow batteries (RFBs) have attracted extensive research interest in recent years due to their low cost, safe operation condition, design flexibility, and easy scalability for large scale energy storage applications. Among all the RFBs, the lithium polysulfide redox flow battery (Li-PS RFB) has been considered as one of the most promising new energy storage systems because of their high theoretical energy density (~2600 Wh/kg and 2199 Wh/L for elemental Li and S) and low material cost.However, despite their great promise, the practical application of Li-PS RFBs has been hindered mainly by the dissolution and shuttling of intermediate polysulfides species that cause rapid capacity decay, low coulombic efficiency, and undesired electrode fouling. This shuttling effect is more detrimental in Li-PS RFBs which doesn’t have carbon matrix to immobilize the solid-state sulfur. To address these issues, an effective strategy is to employ a highly selective membrane separator which can suppress polysulfide crossover while allowing fast lithium-ion conductance. Unfortunately, commercial porous battery separators (e.g. Celgard) cannot be adopted due to their low rejection for polysulfide (PSn-) active species and fast capacity decay. Recent few research works revealed the feasibility of using ion exchange membranes (IEMs) as a barrier layer to selectively transport Li+ ions and block PSn- ions. However, most commercial IEMs are unstable in the organic polysulfide electrolyte because of its high swelling ratio which can cause the electrolytes crossover. Hence, there is a critical need to develop high-performance membrane materials for Li-PS RFB applications.In this work, we will present our recent progress on developing high-performance nanoengineered IEM materials for the Li-PS RFBs which can greatly suppress the polysulfide shuttling while maintaining high Li+ conductivity and mechanical stability. Our biphenyl polymer membrane (BPSA) presents excellent stability for the DOL/DME organic electrolyte solution, exhibiting potential for Li-PS RFBs application. To further improve the selectivity of Li-ion over PS, we developed nanocomposite membranes consisting of carbon nanotubes (CNT), boron nitride nanotubes (BNNT), and BPSA. The CNT layer can act as a PS shielding layer as well as reducing the interfacial resistance of membranes, while the BNNT layer can facilitate heat dissipation and suppressing the lithium dendrite formation. Our composite membranes greatly reduce PS crossover which is lower than commercial Celgard 2325 by 4-order of magnitude (3.5×10-7 cm2/sec vs. 2.2×10-7 cm2/sec), while areal resistance is only 3 times higher than Celgard 2325 (15.12 Ω cm2 vs. 4.64 Ω cm2). As a result, the performance of the Li-PS RFB single cell with our composite membranes is superior to that of Celgard and other commercial IEMs (e.g. Nafion 215) under the same condition. At the 100th cycle, the LiPS RFB capacity with Celgard 2325 loses all initial capacity at 40 cycles, while our composite membrane keeps around 95% of the initial capacity after 100 cycles. More detailed descriptions of ion transport properties, electrochemical properties, and battery performance of the membrane separators will be presented.

Fluorinated sulfonated poly (arylene ether)s bearing semi-crystalline structures for highly conducting and stable proton exchange membranes

An aromatic nucleophilic substitution reaction-based direct polycondensation of 2,2-bis(4-hydroxyphenyl)hexafluoropropane, 1,4-bis(4-fluorobenzoyl)benzene (1,4-FBB), and 3,3′-disulfonate-4,4′-difluorodiphenylsulfone is used to synthesize 1,4-FBB in fluorinated sulfonated semi-crystalline poly (arylene ether) copolymers. The ion exchange capacity, mechanical stability, thermal stability, and oxidative stability of membranes with various degrees of sulfonation and water absorption are studied. 1H nuclear magnetic resonance and atomic force microscopy verify the chemical structure of the synthesized ion exchange membrane. The semi-crystalline 6 F-membrane shows reliable chemical, mechanical, thermal, and electrochemical stability. Compared to Nafion 212®, which is a commercial ion exchange membrane, the semi-crystalline 6 F-membrane shows excellent cell performance as current density is increased. All the results mentioned above indicate that this semi-crystalline 6 F-membrane is a good candidate to replace the commercial membranes.

Modeling and validation of concentration dependence of ion exchange membrane permselectivity: Significance of convection and Manning's counter-ion condensation theory

Electrodialysis, reverse electrodialysis, and related electrochemical processes are increasingly important technologies for water purification and renewable energy generation and storage. The electrical efficiency of these processes is directly related to the permselectivity of the ion exchange membranes (IEMs) – defined as the extent to which the membrane permits the passage of counter-ions (ions of opposite charge to the membrane, e.g., cations for a cation exchange membrane) while blocking passage of co-ions. Permselectivity is not a material constant, but rather depends on the concentration and composition of the electrolyte solutions in contact with the IEM. Thus, even though permselectivity is routinely measured at standardized conditions (usually 0.5 M/0.1 M NaCl or KCl), the practical utility of such data is limited because we lack an accurate, quantitative way of using it to predict permselectivity under relevant process conditions. Moreover, the concentration dependence of IEM permselectivity has historically been studied primarily by evaluating the performance of (reverse) electrodialysis stacks rather than individual membranes, which has made it difficult to relate the concentration dependence of permselectivity to specific membrane characteristics. In this study, we measured the permselectivity of four commercial IEMs in six different concentration gradients employing 4 M and 0.5 M NaCl as the high salt concentration. We then constructed a predictive model of membrane permselectivity based on the extended Nernst-Planck equation and investigated how accounting for convection and electrostatic effects (via Manning's counter-ion condensation theory) affected model accuracy. We demonstrate that accurate, quantitative predictions of IEM permselectivity as a function of external salt concentrations are possible and require knowledge of only four easily measured membrane properties: water uptake, water permeability, charge, and thickness.

Improving the performance of polymer-flooding produced water electrodialysis through the application of pulsed electric field

Concentration polarization and fouling hamper the desalination of polymer-flooding produced water (PFPW) via electrodialysis (ED). This water is an abundant by-product from the oil and gas industry. A common technique to mitigate both problems is the application of pulsed electric field (PEF), which consists in supplying a constant current during a short time (pulse) followed by a time without current (pause). Accordingly, this work evaluated the application of PEF during the ED of PFPW to improve the process performance and to reduce fouling incidences. The experimental work consisted in performing ED batch runs in a laboratory-scale stack containing commercial ion exchange membranes. Synthetic PFPW was desalinated under different operating regimes until a fixed number of charges were passed. After each experiment, a membrane pair was recovered from the stack and analyzed through diverse techniques. The application of PEF improved the ED performance in terms of demineralization percentage and energy consumption, the latter having reductions of 36% compared to the continuous mode. In general, the shorter the pulses, the higher the demineralization rate and the lower the energy consumption. Regarding the application of different pause lengths, longer pauses yielded lower energy consumptions, but also lower demineralization. Amorphous precipitates composed of polymer and calcium fouled most on the anion and cation exchange membranes, independently of the applied current regime, but in a moderate amount. Finally, the present study relates the observed effects of PEF application to the electrophoresis and diffusion of HPAM, and shows that PEF is a sound option to enhance the desalination of PFPW.

Single and binary ion sorption equilibria of monovalent and divalent ions in commercial ion exchange membranes

The co-ion and counter-ion sorption of monovalent (Na+, K+, Cl− and NO3−) and divalent ions (Ca2+ and SO42−) in commercial Neosepta ion exchange membranes were systemically studied in both single and binary salt systems. The new generation of Neosepta cation exchange membrane (CSE) showed a significant difference in water uptake and co-ion sorption compared to the earlier generation (CMX). Use of the Manning model confirmed that there were significant differences between these membranes, with the estimated value of the Manning parameter changing from 1.0 ± 0.1 for CMX to 2.8 ± 0.5 for CSE. There were fewer differences between the two Neosepta anion exchange membranes, AMX and ASE. In single salt solutions, potassium sorbed most strongly into the cation exchange membranes, but in binary salt mixtures, calcium dominated due to Donnan exclusion at low concentrations. While these trends were expected, the sorption behaviour in the anion exchange membranes was more complex. The water uptake of both AMX and ASE was shown to be the greatest in Na2SO4 solutions. This strong water uptake was reflected in strong sorption of sulphate ions in a single salt solution. Conversely, in a binary salt mixture with NaCl, sulphate sorption fell significantly at higher concentrations. This was possibly caused by ion pairing within the solution, as well as the strongly hydrophobic nature of styrene in the charged polymer. Water uptake was lowest in NaNO3 solutions, even though sorption of the nitrate ion was comparable to that of chloride in these single salt solutions. In the binary mixture, nitrate was absorbed more strongly than chloride. These results could be due to the low surface charge density of this ion allowing it to bond more strongly with the hydrophobic polymeric backbone at the exclusion of water and other ions.

Sulfonated polyethersulfone based cation exchange membranes for reverse electrodialysis under high salinity gradients

Salinity Gradient Power - Reverse Electrodialysis (SGP-RED) is a promising membrane-based technology to harvest the energy of mixing from solutions of different ionic concentration. Unfortunately, currently available commercial ion exchange membranes – being not specifically designed for RED – are far from satisfying the requirements of this operation, especially when operated with hyper-concentrated brines. In this work, novel sulfonated polyethersulfone (sPES) cation exchange membranes (CEM) were prepared by phase inversion method and tested under high salinity gradients. Use of 5 M NaCl electrolyte for immersion precipitation coagulation bath facilitated the self-standing membrane formation as a result of the electrostatic interaction between the fixed charged groups and electrolyte solution. Microscopy results revealed that dense or asymmetric membranes with non-connected pores were formed by solvent evaporation or immersion precipitation, respectively. The membranes were characterized for ion exchange capacity, water uptake, charge density and thickness, and further studied by electrochemical impedance spectroscopy. The obtained properties of the newly developed membranes were subsequently compared to those of commercial CMX (Neosepta, Japan) and Fuji-CEM-Type 1 (Fujifilm, The Netherlands) membranes. The asymmetric membranes resulted in a very low resistance especially for high ionic gradients but relatively low permselectivity, while dense membranes still had a low resistance compared to commercial membranes and exhibited high permselectivity. Interestingly, in terms of power density, lab-made membranes outperformed the commercial benchmarks when tested for RED applications with brackish water (0.1 M NaCl)/hypersaline brine (4 M NaCl) feeds; power density of CMX and Fuji-CEM-Type 1 were 3.23 and 3.77 W/m2, respectively, while power density of asymmetric and dense sPES membranes were 3.64 and 3.92 W/m2, respectively.

Influence of Water Uptake, Charge, Manning Parameter, and Contact Angle on Water and Salt Transport in Commercial Ion Exchange Membranes

In electrochemical processes such as electrodialysis or redox flow batteries, where ion exchange membranes (IEMs) play a critical role in process performance, energy losses can be reduced by minimi...

Development of High-Performance Ion Selective Membranes for Lithium Polysulfide Redox Flow Batteries (Li-PS RFBs)

There has been a surge of research interest in the lithium polysulfide (Li-PS) redox flow batteries (RFBs) for large scale energy storage applications because of their high theoretical energy density (~2600 Wh/kg and 2199 Wh/L for elemental Li and S) and low material cost. They also can bring additional advantages, such as design flexibility, easy scalability, and safe operation condition. However, the Li-PS battery systems suffer from polysulfide crossover (polysulfide shuttling) between their two working electrodes which decreases the batteries’ columbic efficiency and shortens their cycle lives. This shuttling effect is more detrimental in Li-PS RFBs which doesn’t have carbon matrix to immobilize the solid-state sulfur. In conventional redox flow batteries (e.g. vanadium redox flow battery), the membrane separators has an important role by suppressing the active species crossover between catholyte and anolyte. However, commercial porous battery separators (e.g. Celgard) cannot be adopted due to their low rejection for polysulfide (PSn-) active species and fast capacity decay. Recent few research works revealed the feasibility of using ion exchange membranes (IEMs) as a barrier layer to selectively transport Li+ ions and block PSn- ions. Unfortunately, most commercial IEMs are unstable in the organic polysulfide electrolyte because of its high swelling ratio which can cause the electrolytes crossover. Hence, there is a critical need to develop high performance membrane materials for the Li-PS RFB applications. In this work, we will present our recent progress on developing novel ion exchange membrane materials for the Li-PS RFBs which can greatly suppress the polysulfide shuttling while maintaining high Li+ conductivity and mechanical stability. Our biphenyl polymer membrane (BP-SA) presents excellent stability the DOL/DME organic electrolyte solution, exhibiting potential for Li-PS RFBs application. We studied its selective ion transport properties through diffusion and electrochemical measurement. Diffusion test shows that there is close to 100 % rejection of Li-PS ions by the BP-SA membrane, while considerable amount of Li-PS crossover was found for Celgard and Nafion. Moreover, the BP-SA membrane possess comparable Li conductivity (0.13 mS/cm2) to Nafion (0.29 mS/cm2) in organic solvent. As a result, the Li-PS single cell with the IEM/Celgard composite membrane shows better efficiencies in comparison to the cell with Celgard 2325. Our results unambiguously demonstrate that the BP-SA membrane has greater Li+/PS anion selectivity than Nafion and can be a promising base material to make separators for Li-PS RFBs.

Correction to "Microstructure Determines Water and Salt Permeation in Commercial Ion-Exchange Membranes".

Correction to "Microstructure Determines Water and Salt Permeation in Commercial Ion-Exchange Membranes".

Green fabrication of pore-filling anion exchange membranes using R2R processing

Pore-filling ion exchange membranes are fabricated by complicated and energy-inefficient processes, use of large amounts of polar organic solvents, and optionally post-modification using acid or base. For green fabrication of pore-filling anion exchange membranes (PAEMs), we optimized the process parameters such as pretreatment time, impregnation time, water amount, and photo-polymerization rate of each step using roll to roll (R2R) equipment. Based on these optimized process parameters, a PAEM of 57.5 cm width and 39 μm thickness completely filled with a photo-cured electrolyte polymer was fabricated by aqueous pretreatment and by using an impregnation solution without toxic organic solvents. The impregnation step was conducted along with photo-polymerization at a line speed of 0.3 m/min without repeated impregnation with R2R equipment. The IEC, resistance, and permselectivity of this PAEM were similar to those of handmade PAEMs. The PAEM exhibited chemical stability in the pH range of 0–12. In addition, the reverse electrodialysis stack assembled with these PAEMs exhibited a higher power density than a stack of commercial ion exchange membranes. These results demonstrate that industrial-scale PAEM can be fabricated through a rapid, simple, environmentally friendly, and energy-efficient R2R process.

Electrodialysis of aqueous NaCl-glycerol solutions: A phenomenological comparison of various ion exchange membranes

Industrial processes such as e.g. oil, fat and resin production and saponification generate large volumes of aqueous NaCl-glycerol containing streams. With typical glycerol concentrations ranging from 5 to 15 % (m/m) and a high salt content, these streams pose a challenge to further processing, both to end-of-pipe treatment as to possible reuse scenarios for organic components and/or salts. Electrodialysis is evaluated as an alternative technology to remove salt from these streams. Salt, glycerol and water transport is studied experimentally through desalination of synthetic solutions for 7 commercial ion exchange membrane pairs, Fumatech (FAB-FKB, FAM-FKM, FAS-FKS), Neosepta (AMX-CMX), PCA (MVA-MVK, SA-MV) and Ralex (AMH-CMH). A phenomenological model is applied i.e. model coefficients are derived from test data through regression analysis to evaluate transport phenomena. Salt transport is found to be related to electromigration only and the NaCl transference number is determined to be highest in AMH-CMH (0.96 ± 0.04) and FKS-FAS (1.01 ± 0.03). Limiting current density is highest for FKS-FAS and lowest for FAM-FKM. Water transport is attributed to electroosmosis and osmosis. Water transference numbers found are similar to those in literature (tW ∼ 7–10). The value of the osmotic coefficients (Pw) differs strongly among the different membrane pairs and is highest for MV-SA Q380 (0.99 × 10−5 ms−1). Glycerol transport is attributed to diffusion and water flux induced cotransport. The diffusion of glycerol differs significantly among all membrane pairs (range 2.06 × 10−8 ms−1 FAB-FKB to 12.4 × 10−8 ms−1 MV-SA). Reflection coefficients differ significantly among membrane pairs but fall within a relative narrow range (0.36–0.75 ms−1). Numerical simulation of batch desalination with the derived transport model identifies current density as the largest contribution to the overall glycerol transport (38%−64%) followed by osmotic co-transport (16%−41%) and glycerol diffusion (9%−28%). A low glycerol/NaCl flux is desirable, this occurs when both initial glycerol/NaCl and NaCl concentrations are low while current density is high.

The nature of two transition times on chronopotentiograms of heterogeneous ion exchange membranes: 2D modelling

Chronopotentiometry is largely used for electrochemical characterization of ion-exchange membranes. Nevertheless, the theory is poorly developed in the range of overlimiting currents. This paper proposes a two dimensional convective-diffusion model of ion transport in electromembrane system in galvanostatic mode. We use direct numerical simulation taking into account electroconvection to develop a comprehensive analysis of mechanisms of reaching transition states, which depend on the parameters of electrically heterogeneous surface of ion exchange membrane. We find that the occurrence of two transition times is typical for the simulated electrodialysis systems with heterogeneous membranes. The value of the first transition time, τ1, is conditioned by the fact that the normal and tangential diffusion delivery of ions from the solution bulk to the conductive membrane areas reaches its limiting value. When τ1 is attained, electroconvective vortices appear at the conductive-nonconductive boundaries. They mix the near-surface solution in the vicinity of these boundaries and increase the delivery of the “fresh” solution to the conductive regions. The second transition time, τ2, is reached when electroconvection-diffusion ion delivery to the overall membrane surface attains its limiting value. At t = τ2, electroconvective vortices whose size is comparable with the diffusion layer thickness arise. Both τ1 and τ2 depend on the size and fraction of conductive regions. In the case of conventional commercial ion-exchange membranes τ1 < τSand and τ2 ≥ τSand.

Microstructure Determines Water and Salt Permeation in Commercial Ion-Exchange Membranes.

Ion-exchange membrane (IEM) performance in electrochemical processes such as fuel cells, redox flow batteries, or reverse electrodialysis (RED) is typically quantified through membrane selectivity and conductivity, which together determine the energy efficiency. However, water and co-ion transport (i.e., osmosis and salt diffusion/fuel crossover) also impact energy efficiency by allowing uncontrolled mixing of the electrolyte solutions to occur. For example, in RED with hypersaline water sources, uncontrolled mixing consumes 20-50% of the available mixing energy. Thus, in addition to high selectivity and high conductivity, it is desirable for IEMs to have low permeability to water and salt to minimize energy losses. Unfortunately, there is very little quantitative water and salt permeability information available for commercial IEMs, making it difficult to select the best membrane for a particular application. Accordingly, we measured the water and salt transport properties of 20 commercial IEMs and analyzed the relationships between permeability, diffusion, and partitioning according to the solution-diffusion model. We found that water and salt permeance vary over several orders of magnitude among commercial IEMs, making some membranes better suited than others to electrochemical processes that involve high salt concentrations and/or concentration gradients. Water and salt diffusion coefficients were found to be the principal factors contributing to the differences in permeance among commercial IEMs. We also observed that water and salt permeability were highly correlated to one another for all IEMs studied, regardless of polymer type or reinforcement. This finding suggests that transport of mobile salt in IEMs is governed by the microstructure of the membrane and provides clear evidence that mobile salt does not interact strongly with polymer chains in highly swollen IEMs.

Optimization of a Novel All-Vanadium Hybrid Redox Flow Battery/Mediator Supercapacitor

The increasing demand for renewable energy is reliant upon progress in energy storage, which is essential in smart-grid and transportation applications. Redox flow batteries have been a promising path for these applications with their very high specific energy, but they suffer from low specific power, slow response, and a low charge rate. In contrast, mediator supercapacitors display high specific power and a fast response rate with a high charge rate, but relatively low specific energy. A hybrid flow-battery/supercapacitor is fabricated and operated under different conditions to provide high specific energy and power along with performance capabilities across a wide range of charge rates, utilizing both physical and chemical charging methods within the cell. The porous electrodes of the electrochemical cell consisted of the Vanadium mediators (VOSO4 and VCl3), supercapacitor carbon black powder, and a polymer binder. A commercial ion exchange membrane was used as the separator. This investigation focuses on the effects of flow rate, charge rate, and mediator concentration on the performance of the hybrid device. Potentiostatic EIS (EIS), Cyclic Charge Discharge (PWR), and Cyclic Voltammetry (CV) measurements were conducted under a wide range of flow rates and mediator concentrations. The electrochemical kinetics of the mediators were evaluated using linear polarization methods. The results indicate that at a given current for PWR tests and scan rate for CV tests, both the flow rate and mediator concentration greatly impact the charge/discharge behavior, the total energy, and the efficiency of the hybrid system. The system performs over a wide range of currents with repeated cycling. A transition between capacitor-like behavior and battery-like behavior is observed.

Ion Diffusion Coefficients in Ion Exchange Membranes: Significance of Counterion Condensation

This study presents a new framework for extracting single ion diffusion coefficients in ion exchange membranes from experimental ion sorption, salt permeability, and ionic conductivity data. The framework was used to calculate cation and anion diffusion coefficients in a series of commercial ion exchange membranes contacted by aqueous NaCl solutions. Counterion diffusion coefficients were greater than co-ion diffusion coefficients for all membranes after accounting for inherent differences due to ion size. A model for ion diffusion coefficients in ion exchange membranes, incorporating ideas from counterion condensation theory, was proposed to interpret the experimental results. The model predicted co-ion diffusion coefficients reasonably well with no adjustable parameters, while a single adjustable parameter was required to accurately describe counterion diffusion coefficients. The results suggest that for cross-linked ion exchange membranes in which counterion condensation occurs condensed counterions mi...

Influence of temperature gradients on mono- and divalent ion transport in electrodialysis at limiting currents

Temperature gradients in electrodialysis (ED) stacks can potentially enhance the efficiency of charge separation and the selective transport of ions. We have previously investigated temperature gradients in the Ohmic regime but not in the limiting current regime, where diffusion of ions towards the membrane determines the transport rate and temperature gradients potentially have the largest influence. In this research, commercial ion exchange membranes (FAS and FKS, FUMATECH, Germany) are used for the investigation of temperature gradients in the limiting current regime. In contrast to the Ohmic regime, we find that heating the diluted stream increases the current obtained (at a constant applied potential) when compared to heating the concentrate stream in systems containing monovalent KCl and NaCl solutions. For mixtures of mono- and divalent ions, the temperature gradient has a larger influence on the selectivity of the separation. If the desalinated stream is heated, divalent Mg2+ ions show a higher transport than the monovalent K+ and Na+ ions. This is due to the enhanced competitive transport of the mono- and divalent ions under the application of a temperature gradient. These results show the potential application and relevance of temperature gradients to enhance the selective separation of mono- and divalent ions.

Electrokinetic stacking on paper-based analytical device by ion concentration polarization with ion exchange membrane interface

Ion concentration polarization (ICP) effect is an effective preconcentration method for charged species in microfluidic systems. In recent years, ICP has also been introduced in paper-based analytical device (PAD) to improve the detection sensitivity. In this paper, a simple and cheap ICP interface was introduced in PAD by using commercial available ion exchange membrane (IEM) that is commonly used in industry. Significant ICP effect was observed by placing the IEM directly on a wetted paper fluidic channel, and electrokinetic stacking of both anion and cation probes was demonstrated with cation exchange membrane (CEM) and anion exchange membrane (AEM), respectively. Simply based on LED illumination and smart phone fluorescent imaging, about 10-fold signal improvement, was achieved for negatively charged fluorescent probes of fluorescein sodium and FITC-BSA with CEM, and 50-fold signal improvement was achieved for positively charged fluorescent probe of rhodamine 6G with AEM. The performance of this PAD was investigated with fluorescein sodium and rhodamine 6G, and the limits of detection of 0.34 and 0.011 μmol L−1 were achieved, respectively. This method provides a cost-effective route for improving the detection sensitivity of charged species on PAD taking advantage of ICP effect.

Aqueous-Processed, High-Capacity Electrodes for Membrane Capacitive Deionization.

Membrane capacitive deionization (MCDI) is a low-cost technology for desalination. Typically, MCDI electrodes are fabricated using a slurry of nanoparticles in an organic solvent along with polyvinylidene fluoride (PVDF) polymeric binder. Recent studies of the environmental impact of CDI have pointed to the organic solvents used in the fabrication of CDI electrodes as key contributors to the overall environmental impact of the technology. Here, we report a scalable, aqueous processing approach to prepare MCDI electrodes using water-soluble polymer poly(vinyl alcohol) (PVA) as a binder and ion-exchange polymer. Electrodes are prepared by depositing aqueous slurry of activated carbon and PVA binder followed by coating with a thin layer of PVA-based cation- or anion-exchange polymer. When coated with ion-exchange layers, the PVA-bound electrodes exhibit salt adsorption capacities up to 14.4 mg/g and charge efficiencies up to 86.3%, higher than typically achieved for activated carbon electrodes with a hydrophobic polymer binder and ion-exchange membranes (5-13 mg/g). Furthermore, when paired with low-resistance commercial ion-exchange membranes, salt adsorption capacities exceed 18 mg/g. Our overall approach demonstrates a simple, environmentally friendly, cost-effective, and scalable method for the fabrication of high-capacity MCDI electrodes.

The Effect of Membrane and Catalyst for Cell Polarization of PEM Water Electrolysis

Commercial proton ion exchange membranes (Nafion 117, Dufont, USA) are generally supplied in the form of Na+ to storage. Pretreatment accelerate the ionic conductivity of membrane by converting the surface of the membrane into the functional group (-SO3H) having the form of proton ion. The pretreatment process may cause a significant increase in the total cost of water electrolysis and sometimes the expected results, i.e. reduction of membrane fouling, may not be achieved. In this study, we investigated the electrochemical characteristics of MEA according to the treatment condition of membrane and the type of catalyst such as Iridium black and Iridium oxide. Electrochemical and surface morphology of MEA were studied by I-V curves, electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM).