Novel proton exchange membranes based on proton conductive sulfonated PAMPS/PSSA-TiO2 hybrid nanoparticles and sulfonated poly (ether ether ketone) for PEMFC

Nanocomposite membranes based on sulfonated poly (ether ether ketone) (SPEEK) and sulfonated core-shell TiO₂ nanoparticles were prepared. TiO₂ nanoparticles were sulfonated by redox polymerization method by using sodium styrene sulfonate (SSA) and 2-acrylamido-2-methyl-1-propane sulfonic acid (AMPS) monomers. The resultant hybrid nanoparticles (PAMPS-gTiO₂ and PSSA-g-TiO₂) were introduced to SPEEK with a sulfonation degree of 68%. Grafting of sulfonated polymers onto TiO₂ nanoparticles enhanced the content of proton transport sites in the membrane, leading to an increase in proton conductivity and power density. Besides, the mechanical and dimensional stabilities of the nanocomposite membranes were also improved compared with pure SPEEK membrane. The maximum power density for membranes containing 7.5 wt% of PAMPS-gTiO₂ and PSSA-g-TiO₂ nanoparticles at 80 °C obtained 283 mW cm⁻² and 245 mW cm⁻², respectively.     

Enhancement in proton conductivity by blending poly(polyoxometalate)-b-poly(hexanoic acid) block copolymers with sulfonated polysulfone

Designing polymer chains which contain building blocks with well-defined dimension is an efficient method to induce microphase separation and regulate the ionic channels of polymer electrolyte membranes (PEMs). In this study, a Wells-Dawson-type polyoxometalate (POM) is synthesized and chemically bonded to a norbornene derivative to prepare poly (POM) blocks. Then the block copolymer poly (POM)₁₀-b-poly (COOH)₃₀₀ is fabricated using poly (POM) and poly (COOH) blocks. Finally, the block copolymer is blended with sulfonated polysulfone (SPS). The electrostatic interactions between the block copolymer and SPS confer the blend membrane with enhanced mechanical and dimensional stabilities. Due to the homogenous distribution of POM clusters and the hydrophilic-hydrophobic interactions between POMs and polymer backbones, the adjacent hydrophilic domains are connected and continuous proton-transfer channels are induced. As a result, the blend membrane displays proton conductivity of 0.053 S cm⁻¹ (25 °C, 100% RH) and 1.5 × 10⁻² S cm⁻¹ (80 °C, 40% RH), which are 2.52 and 6.25 times higher than those of the plain SPS membrane. Furthermore, SPS/POM-BC-30 shows a maximum power density of 164.9 mW cm⁻², which is 54.7% higher than SPS.     

Enhanced proton conductivities of chitosan-based membranes by inorganic solid superacid SO42−–TiO2 coated carbon nanotubes

To increase proton conductivity of chitosan (CS) based polymer electrolyte membranes, a novel nanofiller-solid superacide SO₄^2--TiO₂ (STi) coated carbon nanotubes (STi@CNTs) are introduced into CS matrix to fabricate membranes for polymer electrolyte membrane fuel cells (PEMFCs). Owing to the STi coating, the dispersion ability of CNTs and interfacial bonding are obviously improved, hence, CNTs can more fully play their reinforcing role, which makes the CS/STi@CNTs composite membranes exhibit better mechanical properties than that of pure CS membrane. More importantly, STi possesses excellent proton transport ability and may create facile proton transport channels in the membranes with the help of high aspect ratio of CNTs. Particularly, the CS/STi@CNTs-1 membrane (1 wt% STi@CNTs loading) obtains the highest proton conductivity of 4.2 × 10⁻² S cm^–1 at 80 °C, enhancing by 80% when compared with that of pure CS membrane. In addition, the STi@CNTs also confer the composite membranes low methanol crossover and outstanding cell performance. The maximum power density of the CS/STi@CNTs-1 membrane is 60.7 mW cm⁻² (5 M methanol concentration, 70 °C), while pure CS membrane produces the peak power density of only 39.8 mW cm⁻².     

Design,synthesis and properties of polyaromatics with hydrophobic and hydrophilic long blocks as proton exchange membrane for PEM fuel cell application

A series of the poly(ether ether ketone)s with hydrophobic and hydrophilic long blocks were successfully synthesized by nucleophilic displacement condensation. The polyaromatics with different size of sulfonic acid group clusters were cast from their solutions to produce accordingly membranes. The comprehensive properties of these membranes were then fully characterized by determining the ion-exchange capacity, water uptake, proton conductivity, dimensional stabilities and mechanical properties. The experimental results show that the main properties of the membrane can be tailored by changing the cluster size of sulfonic acid groups or the length of hydrophilic units. The membrane of Block-6c has good mechanical, oxidative and dimensional stabilities together with high proton conductivity (2.09 × 10⁻² S cm⁻¹) at 80 °C under 100% relative humidity. The membranes also possess excellent thermal and dimensional stabilities, therefore, these polymers are potential and promising proton conducting membrane material for PEM full cell applications.     

Highly durable phosphonated graphene oxide doped polyvinylidene fluoride (PVDF) composite membranes

The polyvinylidene fluoride (PVDF) drew great attention over time amongst the hydrocarbon polymer membranes because of its high C–F chemical bond strength. In this work is to increase the proton conductivity of the PVDF polymer by doping phosphonated graphene oxide to its structure and investigate the improvement of the membrane. Different amounts of phosphonated graphene oxide additive (0.5%, 1% and 1.5% w/w) were doped to PVDF polymer on the purpose of synthesizing proton exchange composite membranes. Characterization tests, i.e, water uptake, swelling properties, ion exchange capacity, and proton conductivity of the synthesized membranes were investigated. The electrochemical impedance analysis results of synthesized membranes vary between 0.0224 S cm^-1 for 0.5% graphene oxide doped PVDF (PVDF/0.5PGO) and 0.0867 S cm^-1 for PVDF/1.5GO membrane. The power density values of PVDF/1.5PGO and PVDF/0.5GO are 48 mW cm⁻² and 28 mW cm⁻² at 0.6 V and 100% relative humidity at 80 °C. The experimental results demonstrate the importance of phosphonated graphene oxide doping into the PVDF composite membrane.     

Pore size tuning of Nafion membranes by UV irradiation for enhanced proton conductivity for fuel cell applications

The influence of optimal ultraviolet irradiation of Nafion membranes in enhancing proton conductivity and performance of passive micro-direct methanol fuel cells with silicon micro-flow channels is investigated for the first time. Initially, Nafion membranes are irradiated with different doses of ultraviolet radiation ranging within 0–400 mJ cm⁻² and their water uptake, swelling-ratios, porosity, and proton conductivities are measured using standard procedure. Results show that there is an enhancement in proton conductivity with an optimal dose of 198 mJ cm⁻² ultraviolet radiation. This enhancement is due to optimum photo-crosslinking of –SO₃H species resulting in maximum pore-size which facilitates enhanced proton-hopping from one –SO₃H site to another in the hydrophilic channel. Nafion membranes with three different thicknesses (50 μm, 90 μm and 183 μm) are irradiated with ultraviolet radiation with 198 mJ cm⁻² dose and passive micro-direct methanol fuel cells are assembled with irradiated Nafion proton exchange membranes. The polarization plots are obtained for the assembled devices. Results show an enhancement of power density of devices nearly by a factor of 1.2–1.5 with optimally irradiated membranes indicating that optimum dose of ultraviolet irradiation of Nafion membranes is an effective technique for power enhancement of proton exchange membrane fuel cells which use fuels like methanol, ethanol and hydrogen.     

An enhanced proton conductivity and reduced methanol permeability composite membrane prepared by sulfonated covalent organic nanosheets/Nafion

Sulfonated covalent organic nanosheets (SCONs) with a functional group (−SO₃H) are effective at reducing ion channels length and facilitating proton diffusion, indicating the potential advantage of SCONs in application for proton exchange membranes (PEMs). In this study, Nafion-SCONs composite membranes were prepared by introducing SCONs into a Nafion membrane. The incorporation of SCONs not only improved proton conductivity, but also suppressed methanol permeability. This was due to the even distribution of ion channels, formed by strong electrostatic interaction between the well dispersed SCONs and Nafion polymer molecules. Notably, Nafion-SCONs-0.6 was the best choice of composite membranes. It exhibited enhanced performance, such as high conductivity and low methanol permeability. The direct methanol fuel cell (DMFC) with Nafion-SCONs-0.6 membrane also showed higher power density (118.2 mW cm⁻²), which was 44% higher than the cell comprised of Nafion membrane (81.9 mW cm⁻²) in 2 M methanol at 60 °C. These results enabled us to work on building composite membranes with enhanced properties, made from nanomaterials and polymer molecules.     

4-Aminopyridine grafted sulfonated poly(arylene ether ketone sulfone) proton exchange membrane with high relative selectivity for fuel cells

A series of sulfonated poly(arylene ether ketone sulfone)s polymer having a degree of sulfonation of 80% and a carboxyl group in the side chain (C-SPAEKS) were prepared by polycondensation. The 4-aminopyridine grafted sulfonated poly(arylene ether ketone sulfone)s polymer membranes (SPPs) were prepared by amidation reaction with the carboxyl group to immobilize 4-aminopyridine on the side chain. The ¹H NMR results and Fourier transform infrared of SPP membranes demonstrated the successful grafting of the 4-aminopyridine. Proton conductivity, water absorption, swelling ratio, and thermal stability of different proportions of SPP membranes were investigated under the different conditions. With the increase of pyridine grafting content, the methanol permeability coefficient of the membrane decreased significantly from 8.17 × 10⁻⁷ cm²s⁻¹ to 8.92 × 10⁻⁸ cm²s⁻¹ at 25 °C. And, the proton conductivity and relative selectivity of the membrane were positively correlated with the grafted pyridine content. Among them, the SPP-4 membrane exhibited the highest proton conductivity of 0.088 Scm⁻¹ at 100 °C. The relative selectivity increased from 4.73 × 10⁴ S scm⁻³ to 9.84 × 10⁴ S scm⁻³.     

Synthesis and characterization of a long side-chain double-cation crosslinked anion-exchange membrane based on poly(styrene-b-(ethylene-co-butylene)-b-styrene)

By choosing a triple block polymer, poly(styrene-b-(ethylene-co-butylene)-b-styrene) (SEBS), as the backbone and adopting a long side-chain double-cation crosslinking strategy, a series of SEBS-based anion-exchange membranes (AEMs) was successively synthesized by chloromethylation, quaternization, crosslinking, solution casting, and alkalization. The 70C16-SEBS-TMHDA membrane showed high OH⁻ conductivity (72.13 mS/cm at 80 °C) and excellent alkali stability (only 10.86% degradation in OH⁻ conductivity after soaking in 4-M NaOH for 1700 h at 80 °C). Furthermore, the SR was only 9.3% at 80 °C and the peak power density of the H₂/O₂ single cell was up to 189 mW/cm² at a current density of 350 mA/cm² at 80 °C. By introducing long flexible side chains into a polymer SEBS backbone, the structure of the hydrophilic–hydrophobic microphase separation in the membrane was constructed to improve the ionic conductivity. Additionally, network crosslinked structure improved dimensional stability and mechanical properties.     

Sulfonated poly(arylene ether sulfone)s membranes with distinct microphase-separated morphology for PEMFCs

Copoly (arylene ether sulfone)s was employed for proton exchange membrane preparation via atom transfer radical polymerization followed by mild sulfonation, enhanced phase-separated morphology and favorable proton conductivity were achieved. The comprehensive ex-situ properties of a range of membranes with different ion exchange capacities were characterized alongside the fuel cell performances investigation. The membranes exhibit higher water uptake, which is beneficial to the proton conduction, compared to Nafion® 211 while maintaining similar swelling ratio. The prepared membranes exhibit reasonably high proton conductivity (0.16 S/cm at 85 °C) benefitting from the well-defined microstructure and high connectivity of the hydrophilic domains. Considering the comprehensive property, membrane with moderate ion exchange capacity (1.39 mmol/g) was employed to fabricate the membrane electrode assembly and peak power density of 0.65 W/cm² at 80 °C, 60% relative humidity was achieved for a H₂/O₂ fuel cell, these hydrocarbon membranes can therefore be implemented in PEMFCs.     

The effective methanol-blocking and proton conductivity membranes based on sulfonated poly (ether ether ketone ketone) and polyorganosilicon with functional groups

To solve the conflict between high proton conductivity and low methanol crossover of pristine sulfonated aromatic polymer membranes, the polyorganosilicon doped sulfonated poly (ether ether ketone ketone) (SPEEKK) composite membranes were prepared by introducing polyorganosilicon additive with various functional groups into SPEEKK in this study. Scanning electron microcopy (SEM) images showed the obtained membranes were compact. No apparent agglomerations, cracks and pinholes were observed in the SEM images of composite membranes. The good compatibility between polymer and additive led to the interconnection, thus producing new materials with great characteristics and enhanced performance. Besides, the dual crosslinked structure could be formed in composite membranes through the condensation of silanols and the strong interaction between matrix and additive. The formation of dual crosslinked structure optimized the water absorption, enhanced the hydrolytic stability and oxidative stability of membranes. Especially, the incorporation of additive improved the strength and flexibility of composite membranes at the same time, meaning that the life of the composite membranes might be extended during the fuel cell operation. Meanwhile, the proton conductivity improved with increasing additive content due to the loading of more available acidic groups. It is noteworthy that at 25% additive loading, the proton conductivity reached a maximum value of 5.4 × 10⁻² S cm⁻¹ at 25 °C, which exceeded the corresponding value of Nafion^@ 117 (5.0 × 10⁻² S cm⁻¹) under same experimental conditions. The composite membrane with 20 wt% additive was found to produce the highest selectivity (1.22 × 10⁵ S cm⁻³) with proton conductivity of 4.70 × 10⁻² S cm⁻¹ and methanol diffusion coefficient of 3.85 × 10⁻⁷ cm² s⁻¹, suggesting its best potential as proton exchange membrane for direct methanol fuel cell application. The main novelty of our work is providing a feasible and environment-friendly way to prepare the self-made polyorganosilicon with various functional groups and introducing it into SPEEKK to fabricate the dual crosslinked membranes. This design produces new materials with outstanding performance.     

Proton conduction of novel calcium phosphate nanocomposite membranes for high temperature PEM fuel cells applications

This work describes the synthesis and evaluation of nanocomposite membranes based on calcium phosphate (CP)/ionic liquids (ILs) for high-temperature proton exchange membrane (PEM) fuel cells. Several composite membranes were synthesized by varying the mass ratios of ILs with respect to the CP and all supported on porous polytetrafluoroethylene (PTFE). The membranes exhibit high proton conductivities. Two ionic liquids were investigated in this study, namely, 1-Hexyl-3- methylimidazolium tricyanomethanide, [HMIM][C₄N₃⁻], and 1-Ethyl-3-methylimidazolium methanesulfonate, [EMIM][CH₃O₃S⁻]. At room temperature, the CP/PTFE/[HMIM][C₄N₃⁻] composite membrane possessed a high proton conductivity of 0.1 S cm⁻¹. When processed at 200 °C, and fully anhydrous conditions, the membrane showed a conductivity of 3.14 × 10⁻³ S cm⁻¹. Membranes based on CP/PTFE/[EMIM][CH₃O₃S⁻] on the other hand, had a maximum proton conductivity of 2.06 × 10⁻³ S cm⁻¹ at room temperature. The proton conductivities reported in this work appear promising for the application in high-temperature PEMFCs operated above the boiling point of water.     

In-situ molecular-level hybridization enabling high-sulfonation-degree sulfonated poly(ether ether ketone) membrane with excellent anti-swelling ability and proton conduction

Sulfonated poly(ether ether ketone) (SPEEK) membrane with high sulfonation degree (SD) is a promising substitute of Nafion as proton exchange membrane (PEM), due to the excellent proton conductivity and low cost. However, its widespread application is limited by the inferior structural stability. Here, we report the fabrication of high SD SPEEK membrane with outstanding structural stability through an in-situ molecular-level hybridization method. Concretely, the ionic nanophase of SPEEK membrane is filled with precursors, which are then in-situ converted into polymer quantum dots (PQDs) by a microwave-assisted polycondensation process. In this manner, the micro-phase separation structure of SPEEK membrane is well maintained. PQDs with abundant hydrophilic functional groups together with the inherent –SO₃H groups impart hybrid membrane highly enhanced proton conductivity of 138.2 mS cm⁻¹ at 80 °C, which is comparable to Nafion. This then offers a 116.3% enhancement in device output power. Meanwhile, PQDs act as cross-linkers via generated electrostatic interactions with SPEEK, affording hybrid membrane with SD of 94.1% an ultralow swelling ratio of 1.35% at 25 °C, about 35 times lower than control membrane. More importantly, the in-situ molecular-level hybridization method is versatile, which can also boost the performances of chitosan (CS)-based membranes.     

Novel branched sulfonated poly(arylene ether)s based on carbazole derivative for proton exchange membrane

Proton exchange membrane (PEM) is a vital part of polymer electrolyte fuel cells (PEFCs). So it is of great importance to design the novel polymers for PEMs to improve the performance of PEFCs. Here two highly branched sulfonated copolymers (SBP-Cz-x) were synthesized based on a novel AB₂ monomer. For all we know, it is the first time that the 9H site of carbazole was used to prepare branched polymers. These copolymers given tough and transparent membranes by solvent casting method. SBP-Cz-x membranes exhibited excellent thermal stability and remarkable dimensional stability. Moreover, proton conductivity of SBP-Cz-x was very excellent. SBP-Cz-15 (IEC = 1.33 meq.g⁻¹) owned high proton conductivity of 42.1 mS cm⁻¹ at 80 °C. SBP-Cz-15 showed a pretty low swelling ratio of 12.7% with high water uptake (32.0%). SBP-Cz-x also owned remarkable oxidation stability. This study demonstrated that the strategy of fixing locally dense sulfonic acid groups on the branched points, which were surrounded by hydrophobic segment, could improve oxidative stability and dimensional stability efficiently.     

Synthesis and properties of sulfonated poly(arylene ether ketone sulfone) containing amino groups/functional titania inorganic particles hybrid membranes for fuel cells

In this work, the organic-inorganic hybrid membranes were prepared. The synthesis and properties of the hybrid membranes were investigated. The sulfonated poly(arylene ether ketone sulfone) containing amino groups (Am-SPAEKS) was synthesized by nucleophilic polycondensation. The sol-gel method was used to prepared functional titania inorganic particles (L-TiO₂). The ¹H NMR and FT-IR were performed to verified the structure of Am-SPAEKS and L-TiO₂. The organic-inorganic hybrid membranes showed both good thermal stabilities and mechanical properties than that of Am-SPAEKS. The L-Am-15% membrane exhibited the highest Young's modulus (2262.71 MPa) and Yield stress (62.09 MPa). The distribution of L-TiO₂ particles was revealed by SEM. Compared to Am-SPAEKS, the hybrid membranes showed higher proton conductivities. The L-Am-15% exhibited the highest proton conductivity of 0.0879 S cm⁻¹ at 90 °C. The results indicate that the organic-inorganic hybrid membranes have potential for application in proton exchange membrane fuel cells.     

Quaternary ammonium-functionalized poly(ether sulfone ketone) anion exchange membranes: The effect of block ratios

Anion exchange membranes based on quaternary ammonium-functionalized poly(ether sulfone ketone) block copolymers (QA-PESK) with various hydrophilic–hydrophobic oligomer block ratios (10:7, 10:18, and 10:26) were synthesized, and the block length effect on the membranes' physicochemical and electrical properties were systematically investigated. The QA-PESK-10-18 membrane, prepared using a hydrophilic and hydrophobic block ratio of 10:18, displayed well-balanced hydrophilic/hydrophobic phase separation, the highest conductivity of 23.19 mS cm⁻¹ at 20 °C and 57.84 mS cm⁻¹ at 80 °C, and the highest alkaline stability among the three block ratios tested, indicating that the membranes' properties were closely related to their morphologies, which were determined by the hydrophilic/hydrophobic ratio of the block copolymer. The H₂/O₂ single cell performance using the QA-PESK-10-18 revealed a maximum power density of 235 mW cm⁻².     

Facile synthesis of poly (arylene ether ketone)s containing flexible sulfoalkyl groups with enhanced oxidative stability for DMFCs

After tethering sodium 2-mercaptoethanesulfonate (MTS) to the bromomethylated poly(arylene ether ketone) precursor, a novel clustered sulfonated poly(arylene ether ketone) containing flexible sulfoalkyl groups (MTSPAEK) was prepared and used as polymer electrolyte membrane for application in DMFCs. The chemical structure and the degree of grafting of MTSPAEK copolymers were identified by ¹H NMR spectra. The resulted MTSPAEK copolymers exhibited excellent thermal stability (T_d5% > 259 °C) and good mechanical properties (tensile strength at break > 52 MPa). Compared to conventional sulfonated aromatic hydrocarbon polymers, MTSPAEK membranes displayed enhanced oxidative stability in Fenton's reagent owing to the elimination of free radicals by the sulfide groups located on the polymer side chains. Especially, MTSPAEK-2.10 with the highest content of flexible sulfoalkyl groups exhibited a highest proton conductivity of 0.181 S cm⁻¹ at 80 °C. It could be attributed to the obvious hydrophilic/hydrophobic phase-separated structure within the membrane, which was confirmed by AFM images. Moreover, MTSPAEK-2.10 membrane performed a peak power density of 70 mW cm⁻² in DMFC when feeding with 2 M methanol at 80 °C, which was comparable to the performance of recast Nafion as reported. Therefore, the combination of good thermal stability and mechanical properties, good oxidative stability, and good methanol barrier performance of MTSPAEK membranes indicated that they have potential to be alternative materials for PEMs in DMFCs.     

Constructing a long-range proton conduction bridge in sulfonated polyetheretherketone membranes with low DS by incorporating acid-base bi-functionalized metal organic frameworks

Functionalized metal-organic frameworks (MOFs) are being extensively developed as viable fillers to enhance the proton conductivity of proton exchange membranes. Herein, an amino-pendant sulfonic acid bi-functionalized MOFs material (UNCS)-doped SPEEK membrane with low degree of sulfonation (DS) can improve the proton conductivity as well as maintain the membrane dimensional stability. UNCS can act as bridges of proton donors and acceptors to reduce the activation energy barrier and shorten the distance of long-range proton conduction. Among all as-prepared membranes, SPEEK/UNCS-3 exhibited the highest proton conductivity of 186.4 mS·cm^?1 at 75 °C and 100% relative humidity (RH), which is much greater than that of pristine SPEEK and Nafion 117. Benefiting from the acid-base pair interaction between the amino groups of UNCS and the sulfonic acid groups of SPEEK, the dimensional stability and mechanical properties of the composite membranes were enhanced. More interestingly, STEM-HAADF and SAXS characterization consistently revealed that UNCS served as bridges among proton channels in the composite membranes for continuous proton transport.     

Comb-shaped sulfonated poly(aryl ether sulfone) proton exchange membrane for fuel cell applications

Structure design is the primary strategy to acquire suitable ionomers for preparing proton exchange membranes (PEMs) with excellent performance. A series of comb-shaped sulfonated fluorinated poly(aryl ether sulfone) (SPFAES) membranes are prepared from sulfonated fluorinated poly(aryl ether sulfone) polymer (SPFAE) and sulfonated poly(aryl ether sulfone) oligomer (SPAES-Oligomer). Chemical structures of the comb-shaped membranes are verified by ¹H nuclear magnetic resonance (NMR) and Fourier transform infrared (FT-IR) spectra. The comb-shaped SPFAES membranes display more continuous hydrophilic domains for ion transfer, because the abundant cations and flexible side-chains structure possess higher mobility and hydrophilicity, which show significantly improved proton conductivity, physicochemical stability, mechanical property compared to the linear SPFAE membranes. In a H₂/O₂ single-cell test, the SPFAES-1.77 membrane achieves a higher power density of 699.3 mW/cm² in comparison with Nafion® 112 (618.0 mW/cm²) at 80 °C and 100% relative humidity. This work offers a promising example for the synthesis of highly branched polymers with flexible comb-shaped side chains for high-performance PEMs.     

Influence of composition and acid treatment on proton conduction of composite polybenzimidazole membranes

Inorganic/organic composite membranes formed by polybenzimidazole, silicotungstic acid and silica with different ratio between them have been prepared and characterized before and after treatment in phosphoric acid in order to evaluate the influence of composition and acid treatment on some main characteristics of the membranes. In particular the proton conductivity, the mechanical stability and the structural characteristics of the membranes were evaluated. Silica behaved as a support on which the heteropolyacid remained blocked in finely dispersed state and as an adsorbent for water, thus determining a beneficial effect on proton conduction. The membrane with 50 wt.% of SiWA–SiO₂/PBI, mechanically stable, gave proton conductivity of 1.2×10⁻³ S cm⁻¹ at 160°C and 100% relative humidity. After treatment with phosphoric acid the proton conductivity of membranes increased to 2.23×10⁻³ S cm⁻¹ under the same test conditions. All the materials prepared had amorphous structure.