Decrease In Ion Exchange Capacity Research Articles

Phosphonate poly(vinylbenzyl chloride)-Modified Sulfonated poly(aryl ether nitrile) for Blend Proton Exchange Membranes: Enhanced Mechanical and Electrochemical Properties.

Blend proton exchange membranes (BPEMs) were prepared by blending sulfonated poly(aryl ether nitrile) (SPAEN) with phosphorylated poly(vinylbenzyl chloride) (PPVBC) and named as SPM-x%, where x refers to the proportion of PPVBC to the weight of SPAEN. The chemical complexation interaction between the phosphoric acid and sulfonic acid groups in the PPVBC-SPAEN system resulted in BPEMs with reduced water uptake and enhanced mechanical properties compared to SPAEN proton exchange membranes. Furthermore, the flame retardancy of the PPVBC improved the thermal stability of the BPEMs. Despite a decrease in ion exchange capacity, the proton conductivity of the BPEMs in the through-plane direction was significantly enhanced due to the introduction of phosphoric acid groups, especially in low relative humidity (RH) environments. The measured proton conductivity of SPM-8% was 147, 98, and 28 mS cm-1 under 95%, 70%, and 50% RH, respectively, which is higher than that of the unmodified SPAEN membrane and other SPM-x% membranes. Additionally, the morphology and anisotropy of the membrane proton conductivities were analyzed and discussed. Overall, the results indicated that PPVBC doping can effectively enhance the mechanical and electrochemical properties of SPAEN membranes.

Cross-linked anion exchange membranes with flexible, long-chain, bis-imidazolium cation cross-linker

Herein, poly (phenylene) oxide (PPO)-based cross-linked anion exchange membranes (AEMs) with flexible, long-chain, bis-imidazolium cation cross-linkers are designed and synthesized. Although the cross-linked membranes possess high ion exchange capacity (IEC) values of up to 3.51–3.94 meq g−1, they have a low swelling degree and good mechanical strength because of their cross-linked structure. Though the membranes with the longest flexible bis-imidazolium cation cross-linker (BMImH-PPO) possess the lowest IEC among these PPO-based AEMs, they show the highest conductivity (24.10 mS cm−1 at 20 °C) and highest power density (325.7 mW cm−2 at 60 °C) because of the wide hydrophilic/hydrophobic microphase separation in the membranes that promote the construction of ion transport channels, as confirmed by atom force microscope (AFM) images and the small angle X-ray scattering (SAXS) analyses. Furthermore, the BMImH-PPO samples exhibit good chemical stability (10% and 6% decrease in IEC and conductivity, respectively, in 2 M KOH at 80 °C for 480 h, and a 22% decrease in weight in Fenton's reagent at 60 °C for 120 h), making such cross-linked AEMs potentially applicable in alkaline anion exchange membrane fuel cells.

Dependence of the Transport Properties of Perfluorinated Sulfonated Cation-Exchange Membranes on Ion-Exchange Capacity

The transport properties of ion-exchange membranes depend on many factors, primarily, on ion-exchange capacity and chemical composition. Therefore, the correlation of transport properties with a single particular parameter is generally not quite strict. In this study, the dependence of transport properties of several perfluorinated sulfonated cation-exchange membranes that differ in side chain length and fraction of fragments containing ether groups on ion-exchange capacity is analyzed. It is shown that, with a decrease in the ion-exchange capacity from 1.35 to 0.66 mg-equiv/g, the proton conductivity of membranes contacting water and their diffusion permeability with respect to a 0.1 M HCl solution decrease by two orders of magnitude. A decrease in relative humidity leads to the most significant decrease in the conductivity of membranes with a low ion-exchange capacity. Thus, at a relative humidity of 32%, the conductivity of the studied membranes decreases more than 600-fold with a decrease in ion-exchange capacity. In general, the oxygen permeability of membranes is characterized by a similar dependence. However, in this set of membranes, it varies as little as threefold.

Caveat of High Temperature Accelerated Stability Test for Anion Exchange Membranes

Alkaline stability of hydroxide-conducting anion exchange membranes (AEMs) is a significant requirement for practical applications of alkaline membrane fuel cells. Recently, quaternized aryl ether-free polyaromatics with alkaline stable polymer backbone structure have been receiving much attention as promising materials for AEMs.1 Since a prolonged stability test (≥1000 h) is time-consuming and costly, a harsher test condition at more elevated temperature and higher alkaline concentration to push the limit of AEM stability was advised for degradation and durability studies of such membranes. In this study, we investigate alkaline stability of aryl ether-free Diels-Alder polyphenylene (DAPP) with a trimethylammonium cation attached to an electron-donating hexamethylene spacer2 under low and high temperature (80, 120 and 160 °C) alkaline stability test conditions. Although high temperature stability testing may seem to be a useful tool to measure alkaline stability in a short time period, we observed different phenomena when DAPP AEM was subjected to the extreme test conditions in a pressure vessel. Even though DAPP AEM did not show any structural change or significant decrease in ion exchange capacity or hydroxide conductivity in 4 M NaOH at 80 °C after 3000 h, at the elevated temperature of 160 °C, the membrane underwent instant crosslinking resulted in insolubility of the membrane and sharp decrease in water uptake and swelling degree. The source of crosslinking is the low concentration of residual alkyl bromide from the incomplete quaternization process, which often causes initial conductivity decrease of AEMs. The crosslinked membrane did not show any further change in their properties, exhibiting consistent ion exchange capacity and hydroxide conductivity during the follow-up alkaline stability test (4 M NaOH, 80 °C, 1000 h). In this presentation, structural analysis and membrane properties including ion exchange capacity, water uptake, swelling degree, solubility, mechanical properties and hydroxide conductivity of DAPP AEMs after different temperature alkaline stability testing will be discussed to elucidate the unexpected consequence of high temperature accelerated stability test. References E. J. Park, Y. S. Kim. J. Mater. Chem. A, 2018, 6, 15456–15477.M. R. Hibbs. J. Polym. Sci., Part B: Polym. Phys., 2013, 51, 1736–1742.

Improving the proton conductivity and antibacterial properties of sulfonated polybenzimidazole/ZnO/cellulose with surface functionalized cellulose/ZnO bionanocomposites

New bionanocomposite proton exchange membranes were prepared from sulfonated polybenzimidazole (s-PBI) and various amounts of sulfonated ZnO/cellulose nanohybrids (ZnO/cellulose-SO3H). The use of ZnO/cellulose-SO3H compensates for the decrease in ion exchange capacity of membranes observed when non-sulfonated nano-fillers are utilized. The strong –SO3H/–SO3H interaction between s-PBI chains and ZnO/cellulose-SO3H hybrids leads to ionic cross-linking in the membrane structure, which increases both the thermal stability and methanol resistance of the membranes. The ZnO/cellulose -SO3H in the membranes served as spacers for polymer chains to provide extra space for water permeation, so as to bring high permeation rates to the complex membranes. Moreover, the membranes exhibited excellent antibacterial activities against S. aureus and E. coli. A.

Sulfonated aromatic copoly(ether–amide) membranes II

Several aromatic sulfonated copoly(ether–amide)s, based on the aromatic diamines 4,4′-(hexafluoroisopropylidene)bis(p-phenyleneoxy)-dianiline (HFD) and 2,4-diaminobenzensulfonic acid (DABS) and 4,4′-oxybis(benzoic acid) (OBA), were synthesized through a polycondensation reaction. The sulfonation degree was controlled by introducing different concentrations of 2,4-DABS from 40 mol% up to 80 mol%. Proton nuclear magnetic resonance validated the expected concentrations of sulfonic acid groups in the sulfonated aromatic copoly(ether–amide)s. Thermal decomposition of sulfonic groups was found to initiate at 280°C, while main chain decomposition initiates at 410°C. Proton conductivity between 30°C and 75°C was 19.0 and 45.0 mS/cm, respectively, for the copolymer with the highest concentration of sulfonic groups (–SO3H). Comparison with structurally similar sulfonated copolyamides and copoly(ether–amide)s indicates that these new sulfonated copoly(ether–amide)s based on 4,4′-OBA show improved mechanical properties, but a decrease in ion exchange capacity and proton conductivity.

Effect of a neutral fluorinated network on the properties of a perfluorosulfonic acid ionomer as proton exchange membrane

Proton and water transport properties as well as water sorption, thermomechanical properties, and morphology of a new series of semi-Interpenetrating Polymer Network (semi-IPN) combining perfluorosulfonated ionomer (Aquivion®) with a neutral fluorinated network of composition ranging between 10 and 50 wt% have been studied. When less than 20 wt% of neutral fluorinated network are included, water and proton transport properties of semi-IPNs are enhanced compared to that of Aquivion®, despite of their decrease of ion exchange capacity and their capacity to absorb water. Thermal and chemical stabilities are maintained very close to those of Aquivion®. In addition, these new materials show similar performances in fuel cell operation at 105 °C compared to those of Aquivion®. That evidences that perfluorosulfonated ionomer can be strengthened by association with a neutral fluorinated network.

Hybrid materials based on MF-4SC perfluorinated sulfo cation-exchange membranes and silica with proton-acceptor properties

Hybrid materials based on perfluorinated sulfo cation-exchange MF-4SC membranes with silica nanoparticles in the pores, whose surface is modified by hydrocarbon fragments containing amino groups [3-aminopropyl and 3-(2-imidazolin-1-yl)propyl] that impart it with proton-acceptor properties, were obtained. In has been shown that this modification results in a decrease in ion exchange capacity, water uptake and diffusion permeability of the membranes, whereas the ionic conductivity of the membranes with low content of modifying groups increases in comparison with the membrane that contains only SiO 2 . The observed phenomenon, non-typical of ion-exchange materials, was explained using the model of the semielacticity of membrane pore walls.

Alkaline stability of poly(phenylene)‐based anion exchange membranes with various cations

Anion exchange membranes comprised of a poly(phenylene) backbone and one of five different cationic head‐groups are prepared, briefly characterized, and tested for stability in 4 M KOH at 90 °C. The two membranes with resonance‐stabilized cations (benzyl pentamethylguanidinium and benzyl N‐methylimidazolium) show large (>25%) decreases in both conductivity and ion exchange capacity (IEC) after just one day of testing. The membrane with benzyl trimethylammonium cations shows a 33% loss of conductivity (14% decrease in IEC) after 14 days while the membrane with trimethylammonium cations attached by a hexamethylene spacer shows the least degradation: a 5% loss of conductivity over 14 days with no accompanying loss in IEC. A similar membrane which has a six‐carbon spacer and a ketone adjacent to the phenyl ring shows much lower stability, suggesting that the ketone takes part in degradation reactions. © 2012 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1736–1742, 2013

Crosslinked membranes of sulfonated polyimides for polymer electrolyte fuel cell applications

Abstract: Polymer electrolyte fuel cell performance of crosslinked membranes of sulfonated polyimides based on 2,2′-bis(3-sulfophenoxy) benzidine was investigated at higher temperatures of 90–110 °C, relative humidities of 82–27% RH and pressures of 0.3–0.1 MPa. The operation conditions of temperature, pressure and relative humidity largely affected the PEFC performance in connection with each other. At 90 °C and relatively high humidification of 82/68% RH for hydrogen/air, the cell performance was hardly affected by the pressure and was kept in a high level even at 0.1 MPa. At low humidification of 48% and 27% RH, the cell performance was still kept in a reasonably high level at high pressures above 0.2 MPa, but it largely decreased at low pressures below 0.15 MPa. A slight decrease in ion exchange capacity (IEC) of membrane caused a relatively large decrease in the cell performance at a low relative humidity. With an increase in temperature from 90 to 110 °C, the cell performance largely decreased. For example, the membrane (MX2) with a relatively high IEC of 1.9 mequiv g −1 showed a low maximum output ( W max ) of 0.30 W cm −2 at 110 °C, 0.2 MPa and 49% RH, which was less than a half of the corresponding value (0.71 W cm −2 ) at 90 °C. These results indicate that the back-diffusion of water formed at cathode into membrane became less effective at the lower pressure and the higher temperature and for membrane with the lower IEC, resulting in the larger decrease in through-plane proton conductivity under PEFC operation. At 110 °C, 0.3 MPa and 49% RH, MX2 showed the fairly high PEFC performance and durability.

The stability of semi-interpenetrating polymer networks based on sulfonated polyimide and poly(ethylene glycol) diacrylate for fuel cell applications

A series of the semi-interpenetrating polymer network (semi-IPN) membranes based on sulfonated polyimide and poly(ethylene glycol) diacrylate were prepared and characterized comparing with pure sulfonated polyimide membrane and commercially available membrane, Nafion ® 117. The proton conductivity increased with the increase of poly(ethylene glycol) diacrylate contents in spite of the decrease in ion exchange capacity which is a key factor to improve the proton conductivity. The water stability of semi-IPN membranes containing poly(ethylene glycol) diacrylate is higher than the pure sulfonated polyimide membrane. Morphological structure showed that amorphous nature of the films also increased with the poly(ethylene glycol) diacrylate contents, which could make a crosslink, so that the crystallinity of polyimide could disappear. Semi-IPN membranes based on sulfonated polyimide and poly(ethylene glycol) diacrylate, which show good conductivity comparable to Nafion ® 117 in the range of 20–50% content of poly(ethylene glycol) diacrylate, could be promising proton conducting membranes in fuel cell application.

Proton exchange membranes modified with sulfonated silica nanoparticles for direct methanol fuel cells

Nanocomposite proton exchange membranes were prepared from sulfonated poly(phthalazinone ether ketone) (sPPEK) and various amounts of sulfonated silica nanoparticles (silica-SO 3H). The use of silica-SO 3H compensates for the decrease in ion exchange capacity of membranes observed when non-sulfonated nano-fillers are utilized. The strong –SO 3H/–SO 3H interaction between sPPEK chains and silica-SO 3H particles leads to ionic cross-linking in the membrane structure, which increases both the thermal stability and methanol resistance of the membranes. The membrane with 7.5 phr of silica-SO 3H (phr = g of silica-SO 3H/100 g of sPPEK in membranes) exhibits low methanol crossover, high bound-water content, and a proton conductivity of 3.6 fold increase to that of the pristine sPPEK membrane.

Ex situ hydrolytic degradation of sulfonated polyimide membranes for fuel cells

Ex situ hydrolytic stability of sulfonated polyimide (s-PI) membranes for fuel cells was studied depending on structural and external parameters including the ion exchange capacity, the block character, the temperature and the hydrogen peroxide concentration. Infrared spectroscopy was used to identify and quantify the chemical modifications such as the loss of imide functions and of ionic monomers. The decrease in ion exchange capacity due to the elution of sulfonated oligomers was confirmed by sulfur content analysis. A complete hydrolysis of some of the imide functions is observed leading to polymer chain scissions and to the loss of the mechanical properties. It is shown to be a thermo activated process and the activation energy (60kJ/mol) is found in good agreement with the value determined from fuel cell lifetimes. The degradation in fuel cell conditions is similar but faster than in pure water. The same kinetic can be reproduced ex situ by addition 0.05% of hydrogen peroxide.

Chemical Modification of a Sulfonated Membrane with a Cationic Polyaniline Layer to Improve its Permselectivity

The surface of a cation-exchange membrane (Neosepta) bearing sulfonate groups was modified by a thin polyaniline layer to produce a thin positively charged layer at its surface. This modification induces a slight modification of the surface morphology as evidenced by scanning electron microscopy and a decrease in ion exchange capacity. The presence of the polyaniline layer was confirmed by X-ray photoelectron spectroscopy. The selectivity of the modified and unmodified membranes toward protons vs. metallic cations such as Zn 2 + and Cu 2 + were determined after electrodialysis in a two-compartment electrochemical cell. The data indicate that the transport of the metallic cations is decreased significantly following the modification of the membrane with the cationic polyaniline layer. The latter allows the transport of protons from the catholyte to the anolyte compartment with a much improved selectivity since the divalent cations are excluded from the membrane due to the electrostatic barrier created by the thin protonated polyaniline layer.

Fundamental studies on a new series of anion exchange membranes: effect of simultaneous amination-crosslinking processes on membranes ion-exchange capacity and dimensional stability

The effects of amination time and temperature, the compositions of amination medium on membrane stability and ion-exchange capacity (IEC) are reported in this paper. It is revealed that the membrane’s IEC increases with the amination time and attains to a plateau value after some time which is dependent on the temperature, e.g. 56 h at 10 °C, and 4 h at 45 °C. To consider both the dimensional stability and the amination rate, it is recommended that the amination be conducted at 35 °C for 10 h in most cases. Addition of some ethylenediamine (EDA) to the amination medium is favorable to the membrane stability due to the formation of crosslinking structure in the membrane bone but it will cause a slight decrease in IEC. From both the IEC and the stability points of view, the content of saturated EDA should be controlled within 10% of the whole amination agent. To compare with the previous paper [1], the effect of base membranes on IEC and stability is also investigated. It is shown that the membrane dimensional stability can be improved by aryl substitutions without the change of the membrane IEC. Therefore, there are some alternative ways to increase the membrane stability or mechanical strength, e.g. by an increase in the content of EDA (crosslinking agent) or aryl bromine content, a decrease in amination time and temperature and the content of trimethyl amine, etc. By properly balancing them, a series of anion exchange membranes can be obtained to meet different industrial requirements, such as in diffusional dialysis, electrodialysis and water splitting processes.

Anion exchange membranes prepared by amination of cross-linked membranes having chloromethyl groups with 4-vinylpyridine and trimethylamine

Copolymer membranes composed of chloromethylstyrene and divinylbenzene were reacted with 4-vinylpyridine and then trimethylamine to prepare highly tight anion exchange membranes. When 4-vinylpyridine reacted with chloromethyl groups of the copolymer membranes, 4-vinylpyridine polymerized in the membrane matrix to form a ladder-like polymer, of which one polymer was cross-linked. Consequently, relationships of ion exchange capacity and water content to electrical resistance of the obtained membranes were completely different from those of the anion exchange membranes with benzyl trimethylammonium groups cross-linked with divinylbenzene. With increasing reaction time of the copolymer membranes with 4-vinylpyridine, the electrical resistance of the membranes markedly increased with a small decrease in ion exchange capacity and with the decrease in water content. And fixed ion concentration of the membranes reacted with 4-vinylpyridine and then trimethylamine was higher than that of the membranes with benzyl trimethylammonium groups. These are thought to be because of the formation of a ladder-like polymer in the membrane matrix and the introduction of pyridine unit, which is more hydrophobic and bulkier than trimethylamine. The remarkable decrease in the pore size of the membranes was confirmed by the measurement of the diffusion coefficient of neutral molecules, urea and glucose, through the membranes.

Synthesis of organic-inorganic composite membrane by sol-gel process

Silica was succesfully incorporated into cation exchange polymer membranes, CL-25T and Nafion 417, utilizing sol-gel process. As dipping time increased, increase in silica uptake in membrane was observed. In Nafion 417 membrane, no relationship was found between the silica uptake and the change in ion exchange capacity. But CL-25T which has larger pores than Nafion 417 shows proportional decrease in ion exchange capacity with increasing silica uptake. It suggests that the pore structure of membrane and the size control of silica sol are important to modify the structure of composite membranes. In CL-25T membranes modified by silica, the transport rate of IPA (isopropyl alcohol) increased with increasing OH- concentration on the pore surface.

Stability against oxidation of a type-I anion exchanger. I. The effect of persulfate ion on capacity and swelling

The effect of the strong anionic oxidant persulfate, S 2O 8 2−, on the ion exchange capacity of Bio-Rad AG1-X4 100–200 mesh anion exchange resin was investigated when present as the counterion, i.e., with the exchanger in the reactive persulfate form. The decrease of ion exchange capacity as a function of time and the increase in swelling due to scission of polymer chains by the oxidant were determined. It was found that very little (dry) capacity loss occurred during storage of air-dried S 2O 8 2−-form resins at ambient temperature. However, a progressive decrease in capacity was noted when the resin samples were kept fully water swollen. The potential effect of initial pH was briefly examined. Some experiments with chromate- and vanadate-form resins were also carried out.

Studies of the Synthetic Inorganic Ion Exchanger. II. The Properties of Stannic Phosphate

Abstract A recommended procedure for the preparation of stannic phosphate and a discussion of its ion exchange properties have been presented. Some of the results obtained are as follows. 1) The density of the stannic phosphate is 2.17 g./cm3. 2) Stannic phosphate is a weakly acidic cation exchanger and possesses several dissociable hydrogen atoms in the range of pKa. values. In a weakly acidic solution, in which the exchanger is useful, the exchange group having the pKa value of approximately three is most important. 3) The ion exchange equilibrium can be elucidated by the mass action law. 4) The affinity series for alkali metal coincides with the usual relationship observed in the ion exchange resin. 5) The rate-determining step is assumed to be the migration of ions through the water retained in the gel structure. 6) Stannic phosphate is unstable against heat treatment in air; that is, the separation of alkali metal does not go well with the exchanger dried at 110°C due to the slow rate of exchange. 7) It is fairly stable against heat treatment in water; that is, it undergoes only a slight decrease in ion exchange capacity even when it is treated in water at 250°C for 8 days. 8) It is stable against irradiation of about 109r. 9) The structure of stannic phosphate has been suggested on the basis of its thermal decomposition curve, its exchange capacity, its titration curves, and its X-ray diffraction patterns.

カ焼造粒モンモリロナイトによる放射性イオンの吸着

Although montmorillonite has a high cation exchange capacity, it has undesirable characteristics such as swelling and disintegrating into very fine particles in water, which causes the difficulty to separate them from aqueous phase. To improve these faults, a new stable exchanger has been prepared by the calcination of granular montmorillonite.The decrease of ion exchange capacity due to the calcination was improved by the treatment with hydrochloric acid or sodium hydroxide.It was foud that the Na-form exchanger treated with sodium hydroxide was excellent in the exchange capacity and the decontamination factor for radioactive ions. The linear relationship was foud between the concentration of co-existing Na ion and the adsorbed equilibrium of 137Cs on the montmorillonite, and also between breakthrough ratio of radioactive ion and the effluent volume in the range of rather low breakthrough ratio. It is possible to adopt this new product for the decontamination of radioactive ion in water by the column operation process.