Cross-linked Hybrid Membranes Research Articles

Thermally cross-linked ultra-robust membranes for plasticization resistance and permeation enhancement – A combined theoretical and experimental study

This study reports enhanced flux in plasticization-resistive ultra-robust membranes by thermally cross-linking a blend of carboxylated polyimide (PI) and ladder-like amino-polysilsesquioxane (LAPSQ). A series of BTDA-Durene:DABA PIs (BTDA: 3,3′,4,4′-benzophenonetetracarboxylic dianhydride) with three different 2,3,5,6-tetramethyl-1,4-phenylenediamine (Durene):3,5-diaminobenzoic acid (DABA) molar ratios (3:2, 2:1, and 4:1) exhibited an increase in gas permeability with an increasing Durene:DABA molar ratio before and after dehydration-induced cross-linking; this indicated that the bulky Durene moiety was more critical for flux enhancement than the number of carboxylated sites post-cross-linking. More importantly, the thermally cross-linked PI/LAPSQ (80/20) membrane exhibited a significantly enhanced CO 2 permeability of 817% than that of its pre-crosslinked counterpart without sacrificing CO 2 /N 2 or CO 2 /CH 4 selectivity due to a combination of decarboxylation and amidation-induced cross-linking. Molecular dynamics simulations revealed that such a drastic increase in CO 2 permeability was due to larger and/or more interconnected cavities formed in the thermally cross-linked PI/LAPSQ (80/20) membrane. In addition, it showed a substantial increase in hardness and reduced modulus owing to the rigid double-stranded siloxane backbone of LAPSQ and plasticization resistance up to a CO 2 feed pressure of 22 bar. ● Membranes were cross-linked by decarboxylation/amidation of a hybrid polymer blend. ● Siloxane backbone in cross-linked membranes increased hardness and reduced modulus. ● CO 2 permeability of hybrid membranes increased 817% after thermal cross-linking. ● MD simulations showed cross-linking forms larger and more interconnected cavities. ● Cross-linked hybrid membranes were plasticization resistant up to 22 bar of CO 2 .

In situ implantation of cross-linked functional POSS blocks in Nafion® for high performance direct methanol fuel cells

Polyhedral oligomeric silsesquioxane (POSS) has attracted increasing attention because of its organic/inorganic, nanosize, easily functional nature, especially in the applications of direct methanol fuel cells (DMFCs). In this work, we have successfully synthesized a novel bifunctional POSS (Vi-POSS-SO3Na) with vinyl and sulfonic acid groups by thiol-ene click reaction. Vi-POSS-SO3Na was introduced into Nafion® matrix and cross-linked by in-situ simply thermal treatment. The implantation of the bifunctional POSS filler gives significant improvements in the performance of such proton exchange membranes (PEMs). The cross-linked hybrid membrane with 12 wt% of Vi-POSS-SO3Na (X-Nafion@POSS-12) has a high proton conductivity (121 mS cm−1) at 80 °C, excellent dimensional stability and the lowest methanol permeability (5.4 × 10−8 cm2 s−1). The highest power density of the DMFCs was obtained by using the X-Nafion@POSS-12 as PEM in DMFC at 80 °C, and its value (34.93 mW cm−2) is twice higher than that of Nafion 212 membrane (14.90 mW cm−2). The novel in-situ fabrication method gives a simple and potential approach for the preparation of PEMs used in DMFCs.

Preparation and Properties of Hybrid Silane-crosslinked Sulfonated Poly(aryl ether ketone)s as Proton Exchange Membranes

A series of novel organic-inorganic hybrid proton-conducting electrolyte membranes with silane-crosslinked sulfonated poly(aryl ether ketone)(SC-SPAEK) networks was prepared via a simple procedure that includes solution casting and acid treatment. The organosilicon pendants of the silane-grafted SPAEK, which were expected to serve as coupling and crosslinking agents, were found to play a key role in the homogenous dispersion of inorganic particles and improved the performance of hybrid membranes. The hybrid membranes exhibited enhanced proton conductivity, and SC-SPAEK/TiO2-4 showed an extremely high proton conductivity of 0.1472 S/cm at 100 °C. The crosslinked hybrid membranes also demonstrated good chemical resistance, oxidative stability, and mechanical properties. The crosslinked hybrid membranes with excellent comprehensive performance may be a promising material for proton exchange membrane fuel cells.

Facile one-step fabrication of sulfonated polyhedral oligomeric silsesquioxane cross-linked poly(ether ether ketone) for proton exchange membranes

The simplified structure of sulfonated polyhedral oligomeric silsesquioxane crosslinked poly(ether ether ketone) hybrid membranes.

Effect of “bridge” on the performance of organic-inorganic crosslinked hybrid proton exchange membranes via KH550

Abstract A series of novel organic-inorganic crosslinked hybrid proton exchange membranes were prepared using sulfonated poly(arylene ether ketone sulfone) polymers containing carboxyl groups (C-SPAEKS), (3-aminopropyl)-triethoxysilane (KH550), and tetraethoxysilane (TEOS). KH550 acted as a “bridge” after reacting with carboxyl and sulfonic groups of C-SPAEKS to form covalent and ionic crosslinked structure between the C-SPAEKS and SiO2 phase. The crosslinked hybrid membranes (C-SPAEKS/K-SiO2) were characterized by FT-IR spectroscopy, TGA, and electrochemistry, etc. The thermal stability, mechanical properties and proton conductivity of the crosslinked hybrid membranes were improved by the presence of both crosslinked structure and inorganic phase. The proton conductivity of C-SPAEKS/K-SiO2-8 was recorded as 0.110 S cm−1, higher than that of Nafion® (0.028 S cm−1) at 120 °C. Moreover, the methanol permeability of the C-SPAEKS/K-SiO2-8 was measured as 3.86 × 10−7 cm2 s−1, much lower than that of Nafion® 117 membranes (29.4 × 10−7 cm2 s−1) at 25 °C.

Organic–inorganic hybrid proton-conducting electrolyte membranes based on sulfonated poly(arylene ether sulfone) and SiO2–SO3H network for fuel cells

A series of novel organic–inorganic hybrid proton exchange membranes (PEMs) were prepared from the sulfonated poly(arylene ether sulfone) with 4-amino phenyl pendant groups (Am-SPAES), (3-isocyanatopropyl) triethoxysilane (ICPTES), and 3-(trihydroxysilyl) propane-1-sulfonic acid with covalent bonds to form network using a sol-gel method. The obtained cross-linked hybrid membranes (Am-SPAES/I-SiO2-S) displayed excellent solvent resistance and thermal and mechanical stability. The Am-SPAES/I-SiO2-S membranes with cross-linking network exhibited a higher proton conductivity (0.043 S cm−1 at 20°C) than PEMs without covalent bonds (Am-SPAES/SiO2-S) and the swelling ratio maintained below 17.00% even at 100°C. Most importantly, all of the obtained membranes showed considerably lower methanol permeability than that of Nafion 117. In addition, the chemical structures and morphologies of the hybrid membranes were characterized by Fourier transform infrared spectroscopy and scanning electron microscopy, respectively.

Dielectric behaviour of UV-crosslinked sulfonated poly (ether ether ketone) with methyl cellulose (SPEEK-MC) as proton exchange membrane

Proton exchange membrane materials based on sulfonated poly ether ether ketone (SPEEK) with Methyl Cellulose (MC) are developed by solution cast technique and exposed to UV radiation with Bezoin Ethyl Ether (BEE) as photoinitiator. The addition of MC into SPEEK polymer enhances the conductivity up to 8.7 × 10−3 Scm−1 at 30 °C temperature and 80% relative humidity. This new crosslinked hybrid membrane shows good prospect for the use as proton exchange membrane in fuel cell.

Improvement of pervaporation PVA membranes by the controlled incorporation of fullerenol nanoparticles

This work focuses on the incorporation of fullerenol nanoparticles to get PVA-fullerenol mixed matrix membranes for alcohol dehydration by pervaporation. Cross-linked hybrid membranes based on composites of polyvinyl alcohol (PVA) and low-hydroxylated fullerenol C60(OH)12 have been prepared by two different procedures. To improve the dispersion of the functionalized fullerene in the PVA network, the hydrodynamic properties of PVA, fullerenol and PVA/fullerenol composites in dilute solutions were studied by viscometry and dynamic light scattering. It was shown that the aggregate sizes increased with the increase of fullerenol content in the PVA/fullerenol composite solutions. The effect of low-hydroxylated fullerenol on the structure and morphology of PVA membranes was investigated by small-angle X-ray scattering and atomic force microscopy. It was observed that the incorporation of 5wt.% fullerenol and cross-linking with maleic acid led to a more uniform distribution of the amorphous PVA phase. As a result, membrane transport characteristics were improved for the dehydration of n-butanol–water mixtures by pervaporation. The PVA membranes containing 35wt.% maleic acid and 5wt.% fullerenol exhibited the best transport properties.

Oxygen‐enriching properties of a new hybrid membrane cross‐linked from PDMS and fluorine‐containing silicone resin

A fluorine‐containing silicone resin substituent group,vinyl group, and inorganic framework (SR‐FVI) was synthesized through hydrolytic condensation by using vinyltriethoxysilane, 13‐fluorooctyltriethoxysilane, tetraethoxysilane, and tetramethyldivinyldisiloxane as monomers. A new cross‐linked hybrid membrane (CHM) was prepared with the hydrogen‐containing silicone oil (HSO) as a cross‐linking agent, polydimethylsiloxane containing vinyl group and the SR‐FVI as matrix materials to enhance its membrane‐forming ability and permselectivity. The membrane‐forming process and the cross‐linking reactions between the silicon–hydrogen bond and the vinyl group were carried out simultaneously at room temperature. The effects of the SR‐FVI content in the CHMs, pressure difference, and temperature on the oxygen‐enriching properties were evaluated and discussed. A good equilibrium between membrane‐forming ability and oxygen‐enriching properties was attained, for example, oxygen permeability coefficient and ideal separation factor of the CHM with the SR‐FVI content of 50 wt% at 20°C and 0.10 MPa were 594 Barrer and 3.50, respectively. Compared to cross‐linked PDMS membranes without the SR‐FVI, the CHMs show better gas selectivity and similar gas permeability. The oxygen‐enriching property is attributed to the fluorine‐containing component in the CHM due to its good oxygen solubility. POLYM. ENG. SCI., 53:2328–2335, 2013. © 2013 Society of Plastics Engineers

Chemically stable hybrid polymer electrolyte membranes prepared by silane-crosslinking and thiol-ene click chemistry

A series of cross-linked hybrid membranes with low water uptake, high dimensional stabilities, as well as high oxidative stabilities are prepared by a combination of silane-crosslinking and thiol-ene click chemistry based on a sulfonated poly (arylene ether ketone) (SPAEK) with propenyl groups. 1H NMR measurement and Fourier transform infrared spectroscopy are used to characterize and confirm the chemical structure of SPAEK and its cross-linked hybrid polymer exchange membranes. We also investigate the changes in methanol permeability, proton conductivity and mechanical properties. Our findings demonstrate that the Si–O–Si cross-linked structure makes a great contribution to the improvement of dimensional and chemical stabilities. Therefore, these cross-linked hybrid membranes could be considered as promising materials for direct methanol fuel cell applications.

Novel hybrid polymer electrolyte membranes with high proton conductivity prepared by a silane-crosslinking technique for direct methanol fuel cells

In order to prepare a hybrid proton exchange membrane with low methanol permeability and high proton conductivity, two silane monomers, namely 3-glycidoxypropyl-trimethoxysilane (GPTMS) and 3-mercaptopropyl-trimethoxysilane (MPTMS) are first blended with a sulfonated poly(arylene ether ketone) (SPAEK). Then the blended membrane is heated to induce the grafting of GPTMS onto SPAEK. Finally, a hydrolysis-condensation is performed on the grafted membrane to induce cross-linking. The –SH groups of MPTMS are oxidized to sulfonic acid groups, which are attributed to enhance the proton conductivity of hybrid membranes. Fourier transform infrared spectroscopy is used to characterize and confirm the structures of SPAEK and these cross-linked hybrid membranes. The proton conductivity of a cross-linked hybrid membrane G50M50 reaches up to 0.20 S cm −1 at 80 °C, which is comparable to that of SPAEK and much higher than that of Nafion. Meanwhile, the methanol permeability is nearly three times lower than that of Nafion and two times lower than that of SPAEK. The ion-exchange capacity, water uptake, membrane swelling and thermal stability are also investigated to confirm their applicability in fuel cells.

Crosslinked hybrid membranes based on sulfonated poly(ether ether ketone)/γ-methacryloxypropyltrimethoxysilane/phosphotungstic acid by an in situ sol–gel process for direct methanol fuel cells

Proton exchange membranes with high dimensional stabilities and low water uptakes were constructed by incorporating phosphotungstic acid (PWA) into a cross-linked network composed of a crosslinkable sulfonated poly(ether ether ketone) containing dipropenyl groups (SDPEEK) and γ-methacryloxypropyltrimethoxysilane (KH570). The chemical structures of the hybrid membranes were confirmed by FT-IR spectroscopy and scanning electron microscopy (SEM). The results indicated that PWA particles were well dispersed in these membranes. The influences of the dispersed PWA on the properties of membranes such as thermal stability, water uptake, swelling ratio, proton conductivity, methanol permeability and mechanical property were researched. The addition of KH570-5/PWA in the hybrid membranes contributed to the improvement of the dimensional stabilities. And the hybrid membranes with 10–40wt% PWA showed higher proton conductivities than Nafion 117 at 80 °C, while the methanol permeabilities of these membranes were much lower than that of Nafion 117. The membranes also exhibited excellent mechanical properties. These results imply that the SDPEEK/KH570-5/PWA-x membranes are promising materials in the direct methanol fuel cells (DMFC) applications.

Effects of feed pressure on fluorinated polyimide–organosilicate hybrid membranes

The transport properties of a series of fluorinated polyimide–organosilicate hybrid membranes were characterized as a function of feed pressure to determine the degree of CO 2 plasticization. The pure gas feed pressures ranged from 4 to 30 atm using CO 2 and CH 4 at 35 °C. The sol–gel derived organosilicate domains were formed using partially hydrolyzed alkoxide precursors, which were cross-linked with the polymer matrix. The degree of plasticization was dependent upon the degree of cross-linking, being the lowest in a highly cross-linked hybrid membrane. Separate analysis of the diffusion and sorption behavior of CO 2 and CH 4 suggested that the plasticization phenomenon results more from changes in local chain dynamics rather than increases in free volume due to swelling.