Sulfonated polyimide/chitosan composite membrane for vanadium redox flow battery: Membrane preparation,characterization, and single cell performance

A novel sulfonated polyimide/chitosan (SPI/CS) composite membrane was prepared from self‐made SPI (50% of sulfonation degree) through an immersion and self‐assembly method, which was successfully applied in vanadium redox flow battery (VRB). The proton conductivity of SPI/CS composite membrane is effectively improved compared to the plain SPI membrane. The VO²⁺ permeability coefficient across SPI/CS composite membrane is 1.12 × 10^?7 cm² min^?1, which is only one tenth of that of Nafion® 117 membrane. Meanwhile, the proton selectivity of SPI/CS composite membrane is about eight times higher than that of Nafion® 117 membrane. In addition, the oxidative stability SPI/CS composite membrane is superior to that of pristine SPI membrane. The VRB single cell using SPI/CS composite membrane showed higher energy efficiency (88.6%) than that using Nafion® 117 membrane, indicating that SPI/CS composite membrane is a promising proton conductive membrane for VRB application. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Sulfonation of poly(phthalazinone ether sulfone ketone) by heterogeneous method and its potential application on proton exchange membrane (PEM)

A series of sulfonated PPESK (SPPESKs) were synthesized through a heterogeneous sulfonation process with fuming sulfuric acid as sulfonating agent in a chloroform solvent. Membranes prepared from SPPESKs were investigated and proved to be candidates of proton exchange membrane in fuel cell operating at high temperature and low humidity. The heterogeneous sulfonation reaction is verified to first occur on the interface of the acid phase and the chloroform phase, then went on in the acid phase. SPPESKs with sulfonation degree (DS) up to 2.0 are obtained through a new reprecipitation method. Effects of reaction temperature, reaction time, acid/polymer ratio, and chloroform/polymer ratio on the sulfonation reaction are reported in details. An increase in sulfonation degree results in the increase of hydrophilicity, bringing about a substantial gain in proton conductivity. SPPESK membranes exhibit high water uptake of about 105.4% with DS of 1.01, almost two times higher than that of Nafion® with similar dimensional variation. Conductivity values at 35°C, 60% R.H. ranging from 10^?3 to 10^?2 S/cm were measured, which are comparable to or higher than that of Nafion® 112 (1.635 × 10^?2 S/cm) under the same test condition. Thermogravimetric analysis shows that SPPESK membranes are stable up to 290°C in N₂. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1002–1009, 2007     

Preparation and properties of bisphenol A‐based sulfonated poly(arylene ether sulfone) proton exchange membranes for direct methanol fuel cell

Novel bisphenol A‐based sulfonated poly(arylene ether sulfone) (bi A‐SPAES) copolymers were successfully synthesized via direct copolymerization of disodium 3,3′‐disulfonate‐4,4′‐dichlorodiphenylsulfone, 4,4′‐dichlorodiphenylsulfone, and bisphenol A. The copolymer structure was confirmed by Fourier transform infrared spectra and ¹H NMR analysis. The series of sulfonated copolymers based membranes were prepared and evaluated for proton exchange membranes (PEM). The membranes showed good thermal stability and mechanical property. Transmission electron microscopy was used to obtain the microstructures of the synthesized polymers. The membranes exhibit increased water uptake from 8% to 66%, ion exchange capacities from 0.41 to 2.18 meq/g and proton conductivities (25°C) from 0.012 to 0.102 S/cm with the degree of sulfonation increasing. The proton conductivities of bi A‐SPAES‐6 membrane (0.10–0.15 S/cm) with high‐sulfonated degree are higher than that of Nafion 117 membrane (0.095–0.117 S/cm) at all temperatures (20–100°C). Especially, the methanol diffusion coefficients of membranes (1.7 × 10^?8 cm²/s–8.5 × 10^?7 cm²/s) are much lower than that of Nafion 117 membrane (2.1 × 10^?6 cm²/s). The new synthesized copolymer was therefore proposed as a candidate of material for PEM in direct methanol fuel cell. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

主链组成对低磺化度磺化芳香族聚合物质子交换膜性能的影响

通过改变共聚单体种类,探究主链元素种类对聚合物质子交换膜性能的影响。以3,3'-二磺酸基钠盐-4,4'-二氟二苯砜为磺化单体,4,4'-二氟二苯砜为非磺化单体,4,4'-二羟基二苯醚或4,4'-二巯基二苯硫醚为共聚单体,通过亲核缩聚反应成功可控制备出磺化度分别为30%和50%的磺化聚芳醚砜（SPES）与磺化聚芳硫醚砜（SPTES）。采用流延法制备了两种聚合物的透明坚韧的质子交换膜。研究发现两种聚合物膜均显示出了良好的力学性能以及较为适中的吸水率与溶胀度。两种聚合物质子交换膜的起始分解温度达到250℃,具有良好的热稳定性。随磺化度的升高,两种聚合物膜的吸水率、溶胀率以及质子传导率均升高。由于主链硫较氧原子与苯环的共轭作用更强以及供电子硫原子与吸电子基团的相互作用,SPTES膜较SPES膜表现出更高的玻璃化转变温度（T _g）、更低的溶胀率以及更高质子传导率。其中SPES-50与SPTES-50在80℃、100%RH条件下,质子传导率分别为0.136S/cm与0.142S/cm,表明其作为质子交换膜具有潜在的应用前景。     

Sulfonated Membranes from Random Aramide Copolyisophtalamides with Increasing Sulfonation Degree: Characterization for Possible Use as Solid Electrolyte in Fuel Cell

Sulfonated aromatic random copolyisophthalamides with increasing sulfonation degree were synthesized using different concentrations of 2,4-diaminobenzenosulfonic acid, DABS, and 4,4′-(9-fluorenylidene)diamine, BFA, by direct polycondensation with isophthalic acid, ISO. Ionic membranes from these copolymers were cast from solution using dimethylacetamide, DMAc. The sulfonation degree was confirmed by FT-IR and ¹H NMR. The membranes were thermally stable up 310°C. Water uptake (WU%), Ion Exchange Capacity (IEC) and proton conductive values at room temperature, for the sulfonated membrane with 50 mol.% of DABS (BFAS55), were similar or higher than those obtained for Nafion^® 115, tested under the same conditions.     

Sulfonated poly(ether ether sulfone) copolymers for proton exchange membrane fuel cells

Novel aromatic sulfonated poly(ether ether sulfone)s (SPEESs) with tert‐butyl groups were synthesized by aromatic nucleophilic polycondensation of disodium 3,3′‐disulfonate‐4,4′‐dichlorodiphenylsulfone (SDCDPS), 4,4′‐dichlorodiphenylsulfone (DCDPS), and tert‐butylhydroquinone (TBHQ). The resulting copolymers showed very good thermal stability and could be cast into tough membranes. The morphology of the membranes was investigated with atomic force microscopy. The proton conductivity of SPEES‐40 membranes increased from 0.062 S/cm at 25°C to 0.083 S/cm at 80°C, which was higher than the 0.077 S/cm of Nafion 117 under the same testing conditions. These copolymers are good candidates to be new polymeric electrolyte materials for proton exchange membrane fuel cells. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1443–1450, 2007     

Highly conductive proton exchange membranes based on sulfonated poly(phthalazinone ether sulfone) and cerium sulfophenyl phosphate

Polymer composite membranes based on sulfonated poly(phthalazinone ether sulfone) (SPPES) and cerium sulfophenyl phosphate (CeSPP) are prepared. Three CeSPP concentrations are used: 10, 20, and 30 wt.%. The membranes are characterised by infrared spectroscopy (IR), X-ray diffraction spectroscopy, thermal gravimetric analysis, scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The IR results indicate the formation of intense hydrogen bonds between CeSPP and SPPES molecules. The SEM micrographs show that CeSPP well dispersed in composite membrane. The properties of the membranes are evaluated by their water uptake, ionic exchange capacity, proton conductivity and methanol permeability. The proton conductivity of the SPPES (DS 91%)/CeSPP (30 wt.%) composite membrane (I) reaches 0.384 S/cm at 130 °C and 100% relative humidity, which is three times more than Nafion®117. CeSPP improves the conductivity of composite membranes at a low humidity. At 105 °C and 70% RH, the proton conductivity of membrane (I) is 9.1 × 10⁻² S/cm, while Nafion®117 8.8 × 10⁻³ S/cm. The methanol permeability of membrane (I) is 10⁻⁸ cm²/s. That is much lower than Nafion®117.     

Sulfonated polyimide and poly (ethylene glycol) diacrylate based semi‐interpenetrating polymer network membranes for fuel cells

Semi‐interpenetrating polymer network (semi‐IPN) membranes based on novel sulfonated polyimide (SPI) and poly (ethylene glycol) diacrylate (PEGDA) have been prepared for the fuel cell applications. SPI was synthesized from 1,4,5,8‐naphthalenetetracarboxylic dianhydride, 4,4′‐diaminobiphenyl 2,2′‐disulfonic acid, and 2‐bis [4‐(4‐aminophenoxy) phenyl] hexafluoropropane. PEGDA was polymerized in the presence of SPI to synthesize semi‐IPN membranes of different ionic contents. These membranes were characterized by determining, ion exchange capacity, water uptake, water stability, proton conductivity, and thermal stability. The proton conductivity of the membranes increased with increasing PEGDA content in the order of 10^?1 S cm^?1 at 90°C. These interpenetrating network membranes showed higher water stability than the pure acid polyimide membrane. This study shows that semi‐IPN SPI membranes based on PEGDA which gives hydrophilic group and structural stability can be available candidates comparable to Nafion® 117 over 70°C. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Sulfonated poly(arylene ether ketone)s prepared by direct copolymerization as proton exchange membranes: Synthesis and comparative investigation on transport properties

Sulfonated poly(aryl ether ketone)s (SPAEK) copolymers were synthesized by aromatic nucleophilic polycondensation from 3,3′, 5,5′‐tetramethyl‐4, 4′–biphenol, 1,4‐bis(4‐fluorobenzoyl) benzene, and disulfonated difluorobenzophenone. The SPAEK membranes did not exhibit excessive swelling in hot water and at the same time show the proton conductivities in the range of 0.030 S/cm to 0.099 S/cm at 80°C. The methanol diffusion coefficients of the SPAEK membranes were in the range of 4.7 × 10^?7 to 8.1 × 10^?7cm²/s measured at 25°C. The transport properties of this series of SPAEK copolymers were compared to poly(aryl ether ether ketone)s (SPEEK), poly(aryl ether ether ketone ketone)s (SPEEKK), and Nafion® membranes. It was found that the transport properties (including proton conductivity and methanol permeability) follows the trend of SPEEKK‐60 < SPAEK‐60 < SPEEK‐60 < Nafion® 117, the order of which is also attributed to the differences in the chemical structure of the polymers and the membrane morphology. In general, this novel series of SPAEK membranes possess various advantages, such as low cost of the initial monomers, high thermal and mechanical stability, and low methanol permeability while simultaneously possessing sufficient proton conductivity, which makes them notably promising as proton exchange membrane (PEM) materials in direct methanol fuel cell (DMFC) applications. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Physical and electrochemical behaviors of directly polymerized sulfonated poly(arylene ether ketone sulfone)s proton exchange membranes with different backbone structures

Sulfonated poly(ether ether ketone sulfone) (SPEEKS) and sulfonated poly(ether ether ketone ketone sulfone) (SPEEKKS) copolymers with different degree of sulfonation (DS) were synthesized by aromatic nucleophilic polycondensation of disodium 3,3′‐disulfonate‐4,4′‐dichloro‐diphenylsulfone (SDCDPS), tertbutylhydroquione, and 4,4′‐difluorobenzophenone or 1,4′‐bi(4‐fluorobenzoyl) benzene. Prepared sulfonated copolymers were characterized by Fourier transform infrared spectra, thermogravimetric analysis, and differential scanning calorimetry. The transmission electron microscope was used to investigate the microstructure of membranes. The different distance between two adjacent sulfonic groups in two series of membranes resulted in different physical and electrochemical properties between two kinds of membranes with the same DS. The proton conductivity, ionic exchange capacity and water uptake of SPEEKS membranes were higher than those of SPEEKKS membranes while the mechanical strength of SPEEKS membranes was lower than that of SPEEKKS membranes at the same DS. Moreover, the SPEEKKS membranes with DS equals to 0.8 showed a good combination of a high proton conductivity (0.046 S/cm at 25°C, 0.061 S/cm at 80°C), acceptable water uptake (33–65 wt %), excellent mechanical strength (tensile strength reached 49.7 MPa), and good thermal properties (T_g above 250°C, T_d5% above 300°C). It suggested that this could be a promising membrane for proton exchange membrane fuel cell application. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

A Sulfophenylated Polysulfone as the DMFC Electrolyte Membrane – an Evaluation of Methanol Permeability and Cell Performance

A sulfophenylated polysulfone (PSU‐sph), carrying 0.8 sulfonic acid units per repeating unit of the polymer, is evaluated as a membrane electrolyte for DMFC applications. The liquid uptake, methanol transport characteristics, electrolyte conductivity, and fuel cell performance are investigated. The methanol transport and DMFC performance results are compared to those of Nafion® 117. The PSU‐sph membrane investigated shows superior qualities with regard to methanol crossover, with a methanol permeability of approximately 25% compared to that of Nafion®. The conductivity was measured to be 15% compared to that of Nafion®. However, this could not fully account for the internal resistance of the cell, implying that the contact resistance between the electrodes and electrolyte is higher when PSU‐sph is used, probably because the electrodes are developed for use with Nafion® membranes. The stability of the PSU‐sph membrane seems promising, with very low degradation observed over a period of 72 hours. It was concluded that although the mass transport properties of the PSU‐sph membrane sample investigated were superior, it could not match the performance of Nafion® 117 in a DMFC application. However, a higher degree of sulfonation may have a significant positive effect on cell performance. The results also showed that a fully intergrated MEA is needed to fully assess new menbrane materials.     

Synthesis of Low Methanol Permeation Polymer Electrolyte Membrane from Polystyrene-Butadiene Rubber

In order to find a low cost polymer electrolyte membrane with low methanol cross-over, the development of novel polymer electrolytes have been actively carried out in recent time as alternatives to Nafion®, which is the state-of-the art membrane. The problems associated with these alternative membranes are higher permeability to the fuel, lower proton attraction and thermal stability. This work therefore was focused on synthesizing low methanol permeable membrane with good proton conductvity and thermal stability from locally available polymer (Polystyrene-butadiene rubber). Results obtained revealed that the synthesized membrane exhibited methanol permeation in the ranges of 2.13 × 10^?7 to 7.58 × 10^?7 mol/cm²s which was lower than that of Nafion® (3.15 × 10^?6 cm²/s). The proton conductivity of the synthesized membrane is in the order of 10^?2 S/cm. The results also show that water and solvent uptake of the synthesized membrane are moderate as compared to that of Nafion®. These results are influenced by the degree of sulphonation and membrane thickness ranging from 0.112 mm?0.420 mm.     

Random sulfonated poly(arylene ether sulfone) and sulfonated poly(arylene ether ketone) membranes for fuel cell applications

In this study, sulfonated poly(arylene ether sulfone) (SPAES) and sulfonated poly(arylene ether ketone) (SPAEK) were randomly synthesized, employing a presulfonation process. This presulfonation process resulted in a more controlled and reproducible sulfonation level. The respective polymers were prepared using 2,2-Bis(4-hydroxyphenyl) propane at 50% molar ratio, which also provided some membrane elasticity. The resulting polymers, each had 25% of the block containing the sulfonic domains (SPAES A 25 and SPAEK A 25). Better conductive membranes were achieved for the random sulfone polymers than for the random ketone polymers, with values, respectively, of 0.24 and 0.07 S cm⁻¹ at 80°C. The lower proton conductivity from the ketone-based polymer was compensated with very low methanol permeability (0.25 × 10⁻⁶ cm² s⁻¹) and outstanding oxidative stability. The selectivity of both polymer membranes exceeded the reported values for the state-of-the-art Nafion® 117 and other commercially available options. Both polymer membranes, with their unique combination of ionic domains, elastomeric blocks, and resulting morphology, could be viable candidates for fuel cell applications.     

Effect of sulfonic acid-functionalized polysilsesquioxane on new semifluorinated sulfonated polytriazole composites and investigation of proton exchange membrane properties

A new semifluorinated sulfonated copolytriazole is synthesized, maintaining a particular degree of sulfonation of 80% following the click reaction of two terminal azides 1,4-bis-[{2′-trifluromethyl 4′-(4″-azidophenyl)phenoxy}]phenyl, and 4,4′-diazido-2,2′-stilbenedisulfonic acid disodium salt with equal molar amounts of two dialkyne monomers namely, 1,3-diethynylbenzene and 3,5-bis(prop-2-ynyloxy)benzoic acid and designated as PTEHCSH-80. Further, the copolytriazole is used to prepare polymer composites employing the sol-gel reaction of the starting precursor sol 3-(trihydroxylsilyl) propane-1-sulfonic acid. The weight percentage (wt%) of the filler is varied from 0 to 10 wt%, and a series of polymer composite films are prepared and abbreviated as PTEHCSH-80/X (where X is wt% of the filler, X = 0. 2.5, 5.0, 7.5, 10.0). All the polymer composites are characterized through FTIR spectroscopic techniques. The composite films revealed various desirable properties such as high thermochemical and dimensional and mechanical stabilities in their corresponding acid form. Moreover, the composites exhibited proton conductivities ranging from 62 to 98, 117 to 182, and 131 to 195 mS/cm at three different temperatures 30°C, 80°C, and 90°C, respectively, in a hydrated state.     

Polymer Electrolyte Membrane Based on Sulfonated Poly(Ether Ketone Ether Sulfone) (S-PEKES) with Low Methanol Permeability for Direct Methanol Fuel Cell Application

Poly(ether ketone ether sulfone), (PEKES), was synthesized by the nucleophilic aromatic substitution polycondensation between bisphenol S and 4,4′-difluorobenzophenone (system A), and between bisphenol S and 4,4′-dichlorobenzophenone (system B). The oxidative stability was characterized by using a Fenton's reagent. S-PEKES membranes show a higher thermal stability than that of Nafion 117 and comparable to that of S-PEEK 150XF. The proton conductivity values of S-PEKES of the highest DS are comparable to those of Nafion 117 and S-PEEK. The methanol permeability of the synthesized and fabricated S-PEKES membrane is lower than that of Nafion 117 by at least an order of magnitude.     

Anhydrous proton‐conducting electrolyte based on a nematic poly(methyl acrylate) containing sulfonated side chains

A nematic poly(methyl acrylate) containing terminal sulfonic acids in side chains was prepared by etherification of a brominated mesomorphic precursor with 2‐hydroxyethanesulfonic acid sodium salt. Differential scanning calorimetry measurements and polarized light microscopy observation revealed that the sulfonated polymer exhibited the nematic mesophase at medium temperatures (189–227°C). Electrochemical impedance spectroscopy measurements showed that temperature dependence of anhydrous proton conductivity for the nematic polymer followed the Arrhenius law and that the estimated activation energy was 95 kJ mol⁻¹ in the nematic phase. The proton conductivities of the nematic polymer were two orders of magnitude higher than those of anhydrous Nafion®117 membrane at the same temperature. The enhanced anhydrous proton conductivities of the polymeric electrolyte were ascribed to the orientational order and fluidity of the nematic liquid crystal. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40382.     

Multiblock sulfonated-fluorinated poly(arylene ether)s for a proton exchange membrane fuel cell

New proton exchange membranes were prepared and evaluated as polymer electrolytes for a proton exchange membrane fuel cell (PEMFC). Sulfonated-fluorinated poly(arylene ether) multiblocks (MBs) were synthesized by nucleophilic aromatic substitution of highly activated fluorine terminated telechelics made from decafluorobiphenyl with 4,4′-(hexafluoroisopropylidene)diphenol and hydroxyl-terminated telechelics made from 4,4′-biphenol and 3,3′-disulfonated-4,4′-dichlorodiphenylsulfone. Membranes with various sulfonation levels were successfully cast from N-methyl-2-pyrrolidinone. An increase sulfonated block size in the copolymer resulted in enhanced membrane ion exchange capacity and proton conductivity. The morphological structure of MB copolymers was investigated by tapping mode atomic force microscopy (TM-AFM) and compared with those of Nafion^® and sulfonated poly(arylene ether) random copolymers. AFM images of MBs revealed a very well defined phase separation, which may explain their higher proton conductivities compared to the random copolymers. The results are of particular interest for hydrogen/air fuel cells where conductivity at high temperature and low relative humidity is a critical issue.     

Thermo and electrochemical characterization of sulfonated PEEK–WC membranes and Krytox-Si-Nafion® composite membranes

Two types of membranes, the sulfonated PEEK-WC (poly(oxa-p-phenylene-3,3-phthalido-p-phenylene-oxyphenylene)(SPWC) and Krytox-Si-Nafion® (KSiN) composite membranes are proposed for DMFC applications.The properties based on water uptake, ion exchange capacity, proton conductivity, gas permeability, thermal stabilityand methanol crossover are summarized. The comparative studies on SPWC and Nafion® 117 membranes clarify us that the amorphous sulfonated PEEK-WC polymer shows thermal and mechanical stability with less methanol flux and gas permeability. The membrane also exhibits the increase in water uptake, ion exchange capacity and proton conductivity as sulfuric acid doping agent concentration was increased. The KSiN is unique in term of its miscible hybrid structure of silica particles modified with Nafion® structured Krytox 157 FSL chain (KSi) andNafion®. Based on the KSiN membranes with different KSi content, it was found that when KSi content increased, the reduction of gas permeability, methanol crossover and thermal stability are improved. The composite membrane performs the proton conductivity in the wide range of high temperature (60–130°C).     

Proton Conducting Borosiloxane Solid Electrolytes and Their Composites with Nafion®

A variety of proton conducting borosiloxane solid electrolytes containing -SO₃H groups as proton sources were prepared. The presence of boron as a Lewis acid in the inorganic-organic hybrid structure was thought to lead to enhanced -SO₃H dissociation, while the incorporation of alkyl groups overcame the tendency of the materials towards deliquescence at high temperatures and high relative humidity. Robust films, prepared from composites of borosiloxane electrolyte and Nafion® 117, were thermally stable and exhibited superior proton conducting characteristics to Nafion® 117.     

A low-cost counter electrode of ITO glass coated with a graphene/Nafion® composite film for use in dye-sensitized solar cells

Carbon black (CB), multi-walled carbon nanotube (MWCNT), and graphene (GN) were examined as catalytic films on the counter electrodes (CEs) of dye-sensitized solar cells (DSSCs). GN exhibits the best performance among these materials for the corresponding cell. A composite film of GN/Nafion® was next used as the catalytic film on the CE of a DSSC. Nafion® is demonstrated to be an excellent dispersant for inhibiting the aggregation of GN. A solar-to-electricity conversion efficiency (η) of 8.19% was achieved for the DSSC sensitized by TBA(Ru[(4-carboxylic acid-4′-carboxylate-2,2′-bipyridine)(4,4′-bis(5-(hexylthio)-2,2′-bithien-5′-yl)-2,2′-bipyridine)(NCS)₂]), i.e., CYC-B11 dye, which was synthesized by our group, after the optimization of the composition of GN/Nafion®, and an η of 8.89% was exhibited for the cell with a sputtered-Pt (s-Pt) film on its CE under the same conditions. The significance of the cell with the composite film of GN/Nafion® lies in the fact that the expensive Pt is avoided in this case, thereby the cost of the pertinent DSSC was greatly reduced, even though its η (8.19%) is slightly smaller than that of the cell with the s-Pt film (8.89%).