Long Side Chain PEGMA in Ion Exchange Membranes toward Reducing CO 2 Reduction Product Crossover

Comparison of water and salt transport properties of ion exchange, reverse osmosis, and nanofiltration membranes for desalination and energy applications

In recent years, ion exchange membranes (IEM) have been used successfully to determine the availability of soil nutrient elements for plants. In general, the procedures proposed are applied to the determination of a single ion, and in only a few of these studies, the selectivity of these IEM was considered. Therefore, this work was conducted (a) to find the most suitable extraction conditions for phosphate (H2PO4 ‐), nitrate (NO3 ‐), and sulfate (SO4 2‐) in soils by IEM and their subsequent determination by ion chromatography, (b) to test the effectiveness and selectivity of IEM, (c) to compare the results obtained by IEM with the common procedure for determining the availability of the soil nutrient elements, and (d) to verify whether a relation exits between the concentration of phosphorus (P) extracted by IEM and the plant P requirement. The soil samples used for this study were Humic Cambisols located in four forest plots under natural conditions and four plots fertilized with 100 kg P ha‐1 as triple superphosphate. The efficacy of the IEM was high (85% for SO4 2‐, and 92% for H2PO4 ‐ and NO3 ‐). Statistically significant correlations were obtained between the H2PO4 ‐ extracted by IEM and the H2PO4 ‐ obtained by the Bray P1 procedure (r2=0.936) and with the H2PO4 ‐ extracted using Saunders and Williams (1955) procedure (r2=0.370). The correlation obtained between the amount of NO3 ‐ extracted with IEM and that obtained using 2M potassium chloride (KCl) was also highly significant (r2=0.828). The IEM extraction allowed to know in a single extraction process and a single subsequent measurement by ion chromatography the concentrations of soil available H2PO4 ‐, NO3 ‐, and SO4 2‐ ions, which are of great plant nutrition interest. Phosphorus extractable with IEM yielded a close relationship with biomass production and could be used for determining the P requirement of these forest trees.

Investigation of the adsorption and transport of natural organic matter (NOM) in ion-exchange membranes

The ion exchange membrane is a key component in many electrochemical membrane processes such as fuel cells, flow batteries and electrolysers. Typically, these ion exchange membranes are assembled in stacks and allow the transport of the charge carrying component, i.e. a cation (e.g. proton) or an anion, while retaining the other species and electrolytes preventing their crossover to the other side of the cell. Simultaneously electrons travel through an external circuit powering a device or to store energy.Conventional ion exchange membranes have two major problems: They are based on expensive materials (e.g. Nafion®e. PFSA; perfluorosulfonic acid) or on environmentally harmful chemicals and chemical reactions. Although due to its molecular structure and composition, PFSA membranes show good performances, the major limitation of PFSA membranes is the very high material costs often contributing for more than 35% to the total stack costs [1, 2].One of the major challenges of ion exchange membrane development is the tradeoff between high ion transport rates through the membrane while simultaneously preventing electrolyte crossover [3]. This talk will first present a comprehensive overview of required membrane characteristics and an extensive benchmark study of state-of-the-art performances of ion exchange membranes in different electro-membrane processes. Following on this, the challenges in ion exchange membrane development will be addressed and most importantly two new routes for the development of next generation ion exchange membranes will be presented and their characteristics will be compared to those of a series of extensively benchmarked commercially available ion exchange membranes.The first approach, electrospinning is an effective, versatile method to produce cheap ion exchange membranes [3-6]: Multiple polymers can be employed simultaneously during spinning and this is combined with high degrees of interchain entanglement. This results in an interconnected network of ionic pathways that promote high ionic conductivities confined in a matrix of an inert polymer that guarantees high rejections towards electrolytes to prevent crossover (Figure 1a). Moreover, it is a simple technique that can be easily adapted to large scale production.The second approach uses liquid crystalline (LC) polymers to make ion exchange membranes [7]. This approach has the potential to offer true molecular selectivity and a high degree of flexibility to actually tune this selectivity. LC polymer materials self-organize into structures with well defined isoporosity (Figure 1b). Subsequent template removal or chemical bond cleavage with an acid or base results in the formation of molecular pores. The pores of these materials can be functionalized and depending on the functionality, selectivity can be introduced. Depending on the bulkiness of the functional group also pore sizes can be smaller or bigger. Crosslinking of the formed structures allows control over the swelling of the material and with that reduces crossover. In this way one can rely on both charge-charge interactions as well on size sieving to separate species. The major challenge is the formation of organized structures over larger length scales and the identification of structure-property relationships and with that control over the membrane separation performance.Design principles of both newly developed membrane types are discussed, the membranes are extensively characterized and their performance in electrochemical processes is compared to that of conventional ion exchange membranes. The talk is concluded with a future outlook on the perspectives of ion exchanhe membrane development. T. Cho, et al., Energy Technol. 1 (2013) 596–608. https://doi.org/10.1002/ente.201300108.Lin, et al., J. Electrochem. Soc. 163 (2016) A5049–A5056. https://doi.org/10.1149/2.0071601jes.A. Hugo, et al., Journal of Membrane Science 566 (2018) 406. 10.1016/j.memsci.2018.09.006.Woo Park, et al., J. Membr. Sci. 541 (2017) 85–92. https://doi.org/10.1016/j.memsci.2017.06.086.Choi, et al., Macromolecules. 41 (2008) 4569–4572. https://doi.org/10.1021/ma800551w.J.B. Ballengee, P.N. Pintauro, Macromolecules. 44 (2011) 7307–7314. https://doi.org/10.1021/ma201684j.Kloos, et al., Journal of Membrane Science 620 (2021) 118849. https://doi.org/10.1016/j.memsci.2020.118849 Figure 1

Reverse electrodialysis converts electrochemically into energy conversion technology due to the difference in salinity between diluted salt solutions such as seawater and dilute salt solutions such as fresh water. The RED stack has a cation exchange membrane and anion exchange membrane alternately arranged between two electrodes that selectively transmit anions and cations. Ion exchange membranes are easily contaminated with multivalent ions and organic matter, which affects the performance of RED. In this study, the fouling phenomena of cation and anion exchange membranes for various foulants possibly found in seawater and river water were investigated. Ion exchange membranes were contaminated with NaCl solution containing foulants, and the electrical resistance and the degree of contamination with contamination time were measured. The cation exchange membrane is contaminated with a cationic foulants and the anion exchange membrane is contaminated with anionic foulants. The fouled membranes were regenerated, and the electric resistance and the degree of contamination with regeneration time were measured. Acknowledgment This work was conducted under the framework of Research and Development Program of the Korea Institute of Energy Research (KIER) (B8-2441).

Relationships between transport and physical–mechanical properties of ion exchange membranes

Ion exchange membranes are sensitive indicators of ammonium and nitrate released from green manures with low C/N ratios

Heterogeneous ion-exchange membranes

In an unforced flowing NaCl solution in bulk, gravitational or electro convection supplies ions from bulk toward the membrane surface through a boundary layer. In a boundary layer formed on an anion exchange membrane, the convection converts to migration and diffusion and carries an electric current. In a boundary layer formed on a cation exchange membrane, the convection converts to migration and carry an electric current. In a forced flowing solution in bulk, the boundary layer thickness is reduced and gravitation or electro convection is disappeared. An electric current is carried by diffusion and migration on the anion exchange membrane and by migration on the cation exchange membrane. Ion transport in a boundary layer on the cation exchange membrane immersed in a NaCl solution is more restricted comparing to the phenomenon on the anion exchange membrane. This is due to lower counter-ion mobility in the boundary layer and the restricted water dissociation reaction in the membrane. The water dissociation reaction is generated in an ion exchange membrane and promoted due to the increased forward reaction rate constant. However, the current efficiency for the water dissociation reaction is generally low. The intensity of the water dissociation is more suppressed in the strong acid cation exchange membrane comparing to the phenomenon in the strong base anion exchange membrane due to lower forward reaction rate constant in the cation exchange membrane. In the strong acid cation exchange membrane, the intensity of electric potential is larger than the values in the strong base anion exchange membrane. Accordingly, the stronger repulsive force is developed between ion exchange groups (SO3• groups) and co-ions (OH− ions) in the cation exchange membrane, and the water dissociation reaction is suppressed. In the strong base anion exchange membrane, the repulsive force between ion exchange groups (N+(CH3)3 groups) and co-ions (H+ ions) is relatively low, and the water dissociation reaction is not suppressed. Violent water dissociation is generated in metallic hydroxides precipitated on the desalting surface of the cation exchange membrane. This phenomenon is caused by a catalytic effect of metallic hydroxides. Such violent water dissociation does not occur on the anion exchange membrane.

High-performance ion exchange membranes with high ion exchange capacity (IEC), excellent mechanical properties, lower membrane resistance and superior ions conductivity were developed with chemical-induced polymerization in this work. Through a series of synthesizing experiments, structure characterization and properties testing for polyolefin-based cation exchange membrane (CEM) and anion exchange membrane (AEM), LDPE proved to be an optimized backbone material. The CEM with 57.5% styrene, 38.4% LDPE, 3% crosslinking degree and 1% initiator addition yield the highest IEC value (1.72 mol/g) and moderate burst strength. The 10% addition of styrene was found to enhance IEC of 57% to AEM. However, continually increase styrene leaded lower IEC due to the decreasing grafting degree of vinyl benzene chloride (VBC) on polyethylene. The influence of fillers, such as surface-modified glass fiber (GF) and functionalized graphene oxides (GO), on thermal, mechanical and electrochemical properties of ion exchange membrane were investigated in this work by dynamic mechanical analysis, IEC and field emission scanning electron microscopes (FE-SEM), fourier-transform infrared spectroscopy (FT-IR) and electrochemical impedance spectroscopy. The addition of modified GF increases tensile strength, tensile modulus, storage modulus and interfacial adhesion of GF/CEM composite but degraded the strains. The composite with [3-(Methacryloxy) propyl] trimethoxy silane (3-MPS) modified GF obtained superior mechanical properties and interfacial adhesion, whereas the modified effect of triethoxyvinylsilane (TES) was inconspicuous. The addition of unmodified GF even had negative effects on GF/CEM mechanical properties. The FE-SEM showed that the GF treated by 3-MPS and poly(propylene-graft-maleic anhydride) (PP-g-MA) have better compatibility with the CEM matrix than 1,6 bis and TES treated GF. The FT-IR verified the strengthening effects from modified GF were attributed to the formation of Si-O-Si and Si-O-C bonds. The additions of modified GF in CEM positively influence water uptake ability but negatively on IEC. This section provided a way of strengthening GF/CEM composite. The CEM doped with functionalized graphene oxides was verified to be significantly improved in IEC (21% higher) and membrane conductivity (326.7% higher) compare to the pristine CEM. The results also suggested that the improved effects of dual-functionalized GO on CEM properties are superior to the single functionalized GO. The coexistence of -PO3H, -SO3H in GO resulted in CEM possessed 7.8% higher IEC, 77.29% higher membrane conductivity and 43.56% lower activation energy than that with single functionalized GO. This work provides a new strategy for the design of high-performance IEM with excellent mechanical property, high IEC, high conductivity and low membrane resistance

The rational design of ion exchange membranes (IEMs) is becoming more pertinent as their usage becomes broader and as their staple applications (i.e., electrodialysis, flow batteries, and fuel cells) improve in commercial viability. Such efforts would be catalyzed by an improved fundamental understanding of ion transport in IEMs. This review discusses recent progress in modeling ion partitioning and diffusion in IEMs in an effort to relate IEM performance metrics to fundamental membrane properties over which researchers and membrane manufacturers possess direct and sometimes precise control. Central focus is given to the Donnan‐Manning model for ion partitioning and the Manning‐Meares model for ion diffusion in IEMs. These two frameworks, which are derived from Manning's counter‐ion condensation theory for polyelectrolyte solutions, have been widely used within the IEM literature since their recent introduction. To explore this topic, the mathematical derivation of both models is revisited, followed by a survey of experimental and computational discussions of counter‐ion condensation in IEMs. Alternative models which fulfill similar roles in predicting IEM transport properties are compared. This review concludes by highlighting the uniquely favorable positions of the Donnan‐Manning and Manning‐Meares models and discussing their prospects as leading predictors of IEM partitioning and diffusive properties.

Recent research trends in the development of ion exchange membranes and their use in separation processes with chemical reactions are reviewed. Emphasis in research on the ion exchange membrane is trending toward analysis of micro-structure of the membranes and to development of new functionalized ion exchange membranes in response to industrial requirements. Separation processes with chemical reactions are discussed according to the following classifications: (1) double decomposition of electrolytes; (2) production of acid and base by bipolar ion exchange membrane processes; (3) separators for electrolysis; (4) separators for batteries; (5) use as solid polyelectrolytes; (6) active transport through ion exchange membranes; (7) acceleration of chemical reactions by ion exchange membranes; (8) carrier transport in ion exchange membranes; (9) transducers for electrical signals from chemical reactions; and (10) modified electrodes.

The point of use (POU) HF purification performance of an ion exchange membrane (IEM) is evaluated in this paper. First, no cationic extractable (i.e., Cu, Fe, and Ni) from two IEMs was detected in HF 0.5% which makes these membranes compatible with sub‐ppb grade HF. The IEM purification performance was evaluated with 0.5% HF spiked with 10 ppb of Fe, Ni, and Cu nitrates. The results show that after less than five turnovers through an IEM, the impurity concentration drops below 1 ppb. The decrease rate can be fitted to a model assuming the experimental tanks to be continuously stirred tank reactors and that the impurity concentration after the membrane is a function of the single‐pass purification efficiency of the IEM, the concentration before purification, and the metals desorbed from the IEM. The concentration after purification was investigated up to a cumulative Fe loading of 300 ppb in the 23 liter recirculated loop. It increases linearly vs. cumulative loading and can be explained by the Langmuir theory resulting in a purification efficiency at the equilibrium of close to 99.5% in this loading regime. This suggests that the capacity of the membrane is high enough to ensure an adequate lifetime. Finally, a POU IEM can reduce the Cu concentration in the bath resulting in less Cu outplating. No impact was noticed on particle and organic deposition, on surface roughness, and on 5 nm gate oxide integrity.

As the world produces more renewable energy in the need to transition away from fossil fuels, the use of low-temperature electrochemical reactors is an increasingly important topic of research. An enabling component of electrochemical reactors is an ion exchange membrane, which selectively transports either cations, in a cation exchange membrane (CEM), or anions, in an anion exchange membrane (AEM), from one compartment of a reactor to another. When a CEM and AEM are physically combined they can create a bipolar membrane (BPM), which can generate protons and hydroxide ions from water dissociation at the junction of the AEM and CEM when operated in reverse bias, while also reducing unwanted ion crossover in electrodialysis and electrolysis applications. Maintaining the junction interface is critical to the operation of a BPM, however due to the small size of the junction and the similarities of appearance between the AEM and CEM, it is difficult to obtain spectroscopic information about the BPM junctions. Additionally, in the literature the mechanism behind BPM failures are not well reported. These gaps in knowledge make rational design for improved membranes hard to achieve. Here, we use Confocal Raman Spectroscopy (CRS) to spatially observe spectral data throughout the AEM, CEM and AEM/CEM junction of a novel 3D spun bipolar membrane. CRS uses a monochromatic light to initiate and observe Raman scattering from the polymers in each membrane, showing characteristics of the polymer backbone structure, linkers, and ion exchange functional groups, throughout the membrane thickness. The confocal Raman microscope enables spectrum collection from a micron scale voxel, as opposed to the bulk volume, resulting in a nominally non-destructive technique for making spatiotemporal measurements. Using CRS, we identify the BPM junction thickness and homogeneity through 3-dimensional spatial mapping. We also demonstrate the ability of CRS to analyze the method of BPM failure when used in an electrodialysis reactor by obtaining spectral maps of failed membranes, showing junction delamination, ionic buildup in either the CEM or AEM, and ionic polymer breakdowns of the CEM or AEM due to contaminants. In collaboration with experimental collaborators, 3D BPM fabrication techniques were assessed for their impact on overall BPM performance and durability, while demonstrating the non-destructive usage of the CRS technique.

Grain ion-exchangers, as well as ion exchange — membranes are known as crosslinked polyelectrolytes. Ion exchange membranes have been recently used as selective separators in stacks of electrodialisiss and as solid electrolytes in membrane fuel cells. Few years ago, the ion exchange membranes were used in the electrochemical converter and as model substances in biophysics. Now, the mechanism of injection and colletion of ions in dielectric liquids using either ion-exchange membranes is being studied. Controlled injection and collection processes are needed in the field of fundamental research on liquid dielectrics (conduction breakdown, electrohydrodynamics), electrooptics and liquid crystals, as well as in the field of electronic or electric engineering. Ion-exchange membranes are used as ion-collectors or as injectors.