Phosphoric acid doped sulfonated poly(tetra phenyl isoquinoline ether sulfone) copolymers for high temperature proton exchange membrane potential application

Phosphoric acid-doped sulfonated poly(tetra phenyl isoquinoline ether sulfone)s (PA-SPTPIESs) were successfully synthesized for high temperature proton exchange membrane. Poly(tetra phenyl ether ketone sulfone)s (PTPEKS) were prepared from 1,2-bis(4-fluorobenzoyl)-3,4,5,6-tetraphenyl benzene (BFBTPB) and bis(4-fluorohenyl) sulfone with bis(4-hydroxyphenyl) sulfone. The synthesis of the poly(tetra phenyl isoquinoline ether sulfone)s (PTPIESs), was carried out via an intramolecular ring-closure reaction of dibenzoylbenzene of PTPEKS with benzylamine. The sulfonated poly(tetra phenyl isoquinoline ether sulfone)s (SPTPIESs) were obtained by following sulfonation with concentrated sulfuric acid and doped by phosphoric acid. Different contents of sulfonated unit on PTPIESs (8, 12, 16 mol% of BFBTPB) and PA-SPTPIESs were studied by FT-IR, ¹H NMR spectroscopy, and thermogravimetric analysis (TGA). Strong acid–base interaction effect between poly benzisoquinoline (PBI) and sulfonic acid groups formed ionic crosslinking network between polymer chains. The ion exchange capacity (IEC) and proton conductivity of PA-SPTPIESs were evaluated with degree of sulfonation and doping of phosphoric acid.     

Preparation and characterization of sulfonated poly(tetra phenyl ether ketone sulfone)s for proton exchange membrane fuel cell

Sulfonated poly(tetra phenyl ether ketone sulfone)s SPTPEKS were successfully synthesized for proton exchange membrane. Poly(tetra phenyl ether ketone sulfone)s PTPEKS were prepared by the 4,4′-dihydroxydiphenylsulfone with 1,2-bis(4-fluorobenzoyl)-3,4,5,6-tetraphenylbenzene (BFBTPB) and 4,4′-difluorodiphenylsulfone, respectively, at 210 °C using potassium carbonate in sulfolane. PTPEKS were followed by sulfonation using chlorosulfonic acid and concentrated sulfuric acid at two stage reactions. Different contents of sulfonated unit of SPTPEKS (17, 20, 23 mol% of BFBTPB) were studied by FT-IR, ¹H NMR spectroscopy, and thermo gravimetric analysis (TGA). Sorption experiments were conducted to observe the interaction of sulfonated polymers with water. The ion exchange capacity (IEC) and proton conductivity of SPTPEKS were evaluated with increase of degree of sulfonation. The water uptake of synthesized SPTPEKS membranes exhibit 25–61% compared with 28% of Nafion 211^®. The SPTPEKS membranes exhibit proton conductivities (25 °C) of 11.7–25.3 × 10⁻³ S/cm compared with 33.7 × 10⁻³ S/cm of Nafion 211^®.     

Synthesis and characterization of novel cardo poly(aryl ether sulfone) bearing zwitterionic side groups for proton exchange membranes

A novel series of sulfonated poly(aryl ether sulfone)s with zwitterionic groups ([-CH₂CH₂CH₂N⁺CH₃(CH₂CH₂SO₃⁻)₂]) have been prepared by the copolycondensation of a secondary amine-containing biphenol monomer with 4,4′-biphenol and 4,4′-dichlorodiphenylsulfone, and this was followed by the reaction with sodium 2-bromoethanesulfonate. All the resulting copolymers can form uniform and tough membranes by simple solution casting. The investigation of ion exchange capacity (IEC) values indicated that each ammonium group interacted with one sulfonate group. Because of strong intermolecular interaction, the increased packing density of chain formed that resulted in polymer membranes with lower water uptake and swelling ratio, and better oxidative stability compared with side-chain-type sulfonated poly(aryl ether sulfone)s with the close IEC values. The polymer membranes bearing zwitterionic groups kept intact in Fenton’s reagent at 80 °C for 20 h. Furthermore, these membranes demonstrated higher proton conductivity than the side-chain-type sulfonated polymer membranes at the same measurement conditions.     

Composite membranes based on a sulfonated poly(arylene ether sulfone) and proton-conducting hybrid silica particles for high temperature PEMFCs

The organic-inorganic composite membranes are prepared by inserting poly(styrene sulfonate)-grafted silica particles into a polymer matrix of sulfonated poly(arylene ether sulfone) copolymer. The first step consisted in using atom transfer radical polymerization method to prepare surface-modified silica particles grafted with sodium 4-styrenesulfonate, referred to as PSS-g-SiO₂. Ion exchange capacities up to 2.4 meq/g are obtained for these modified silica particles. In a second step, a sulfonated poly(arylene ether sulfone) copolymer is synthesized via nucleophilic step polymerization of sulfonated 4,4′-dichlorodiphenyl sulfone, 4,4′-dichlorodiphenyl sulfone and phenolphthalin monomers in the presence of potassium carbonate. The copolymer is blended with various amounts of silica particles to form organic-inorganic composite membranes. Esterification reaction is carried out between silica particles and the sulfonated polymer chains by thermal treatment in the presence of sodium hypophosphite, which catalyzed the esterification reaction. The water uptake, proton conductivity, and thermal decomposition temperature of the membranes are measured. All composite membranes show better water uptake and proton conductivity than the unmodified membrane. Moreover, the membranes are tested in a commercial single cell at 80 °C and 120 °C in humidified H₂/air under different relative humidity conditions. The composite membrane containing 10%(w/w) of PSS-g-SiO₂ particles, which have ester bonds between polymer chains and silica particles, showed the best performance of 690 mA cm⁻² at 0.6 V, 120 °C and 30 %RH, even higher than the commercial Nafion^® 112 membrane.     

Novel sulfonated poly(phthalazinone ether ketone) ionomers containing benzonitrile moiety for PEM fuel cell applications

A series of benzonitrile-containing sulfonated poly(phthalazinone ether ketone) ionomers were successfully synthesized via the direct copolymerization of benzonitrile-containing bis(phthalazinone), 3,3′-sulfonated-4,4′-difluorodiphenyl ketone and 4,4′-difluoro-diphenyl ketone. The sulfonation degrees can been readily controlled by changing the feed ratio of monomers. The resulting sulfonated polymers with inherent viscosity ranging from 0.45 to 0.72 dL g⁻¹ were characterized by ¹H NMR and other technologies. These sulfonated polymers had good solubility in polar aprotic solvents and afforded tough and ductile membranes by casting from DMAc solution at 60 °C. Due to the specially designed chemical structures, the membranes showed excellent thermal and oxidative stabilities. Thermogravimetric analysis (TGA) traces demonstrated that all the sulfonated polymers exhibited good thermal stability with initial weight loss > 220 °C. The membranes exhibited superior oxidative and hydrolytic stabilities as evidenced by Fenton's reagent. The membranes showed moderate water uptake in low sulfonation degree (≦1.2), and the proton conductivity of the membrane with sulfonation degree of 1.2 was 1.03 × 10⁻³ S cm⁻¹ at 25 °C and 100% relative humidity. The proton conducting and other properties as a membrane can be tailorated by controlling the sulfonation degree.     

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.     

New highly proton-conducting membrane based on sulfonated poly(arylene ether sulfone)s containing fluorophenyl pendant groups,for low-temperature polymer electrolyte membrane fuel cells

A novel series of sulfonated poly(arylene ether sulfone)s (SPAESs) containing fluorophenyl pendant groups are successfully developed and their membranes are evaluated in low-temperature proton exchange membrane fuel cells. The SPAESs are synthesized from 4,4′-dichlorodiphenylsulfone (DCDPS), 3,3′-disulfonate-4,4′-dichlorodiphenylsulfone (SDCDPS), and (4-fluorophenyl)hydroquinone by nucleophilic aromatic substitution polycondensation. The structure and properties of SPAESs membranes are characterized using ¹H-NMR, EA, FT-IR, TG, and DSC, along with the proton conductivity, water uptake, ion exchange capacity and chemical stability. A maximum proton conductivity of 0.35 S cm⁻¹ at 90 °C is achieved for SPAES membrane with 50% SDCDPS. These SPAES membranes display high dimensional stability and oxidative durability, due to the introduction of fluorophenyl pendant groups on the polymer backbone. The fuel cell performances of the MEAs with SPAES reaches an initial power density of 120.6 mW cm⁻² at 30 °C, and greatly increases to 224.3 mW cm⁻² at 80 °C using H₂ and O₂ gases.     

Anion conductive poly(tetraphenyl phthalazine ether sulfone) containing tetra quaternary ammonium hydroxide for alkaline fuel cell application

The poly(tetraphenyl ether ketone sulfone)s (PTPEKSs) were synthesized from 1,2-bis(4-fluorobenzoyl)-3,4,5,6-tetraphenyl benzene (BFBTPB) and bis(4-fluorophenyl) sulfone with bis(4-hydroxydiphenyl) sulfone in sulfolane. The synthesis of poly(tetraphenyl phthalazine ether sulfone)s (PTPPESs) was carried out via an intramolecular ring-closure reaction of dibenzoylbenzene moiety with hydrazine monohydrate. The PTPPES-QAHs [poly(tetraphenyl phthalazine ether sulfone-quaternary ammonium hydroxide)]s were synthesized via chloromethylation of PTPPES, quaternization with trimethylamine, and followed by an anion exchange of tetra-quaternary ammonium chloride polymers with KOH. Different contents of quaternized unit in PTPPES-QAH (15, 20, 25 mol% of BFBTPB) were studied by FT-IR, ¹H NMR spectroscopy, and thermogravimetric analysis (TGA). Sorption experiments were conducted to observe the interaction of quaternized polymers with water. The ion exchange capacity (IEC), ion conductivity and cell performance of PTPPES-QAH were evaluated with increasing the degree of quaternization.     

Cross-linked sulfonated poly(phathalazinone ether ketone)s for PEM fuel cell application as proton-exchange membrane

The cross-linkable sulfonated ploy(arylene ether)s derived from 3,3′-diallyl-4,4′-dihydroxybiphenyl, bisphthalazinone, 4,4′-difluorobenzophenone (DFBP) and sulfonated 4,4′-diflourobenzophenone (SDFBP) were synthesized over a wide range of DFBP/SDFBP molar ratios. The resulting sulfonated poly(arylene ether)s with high inherent viscosity (1.02–1.29 dL g⁻¹) are soluble in polar organic solvents and can form flexible and transparent membranes by casting from their solution. Cross-linking reaction was carried out using the thermal activated radical cross-linking agent (TARC) at 140 °C. The comprehensive properties of the virgin and the cross-linked membranes were compared accordingly. The results showed that the cross-linked membranes revealed the better mechanical, oxidative and dimensional stabilities together with high proton conductivity (9.675 × 10⁻³ S cm⁻¹) at 25 °C under 100% relative humidity.     

Synthesis and properties of hexafluoroisopropylidene-containing sulfonated poly(arylene thioether phosphine oxide)s for proton exchange membranes

A series of novel sulfonated poly(arylene thioether phosphine oxide)s with hexafluoroisopropylidene moieties (sPTPOF) were prepared by polycondensation of sulfonated bis(4-fluorophenyl)phenyl phosphine oxide and bis(4-fluorophenyl)phenyl phosphine oxide with 4,4′-(hexafluoroisopropylidene) diphenthiol. The incorporation of hexafluoroisopropylidene moieties to the resulting polymers is effective to increase the hydrophobicity of non-sulfonated segments and to decrease the swelling while maintaining high proton conductivity. For instance, sPTPOF-100 showed a proton conductivity of 0.090 S/cm as well as a swelling of 5.3% at 80 °C. In addition, the sPTPOF polymers exhibited excellent thermal properties and oxidative stability. AFM phase images illustrated that the sPTPOF membranes show a special nanophase-separated morphology, namely, the connectivity of ionic channels increased obviously but their width only slightly increased with increasing sulfonation degree. This special microstructure is favorable for promoting proton transport and restraining the swelling. The sPTPOF polymers are a promising material for proton exchange membranes.     

Crosslinked sulfonated poly(arylene ether sulfone) membranes for fuel cell application

A series of sulfonated poly(arylene ether sulfone) with photocrosslinkable moieties is successfully synthesized by direct copolymerization of 3,3′-disulfonated 4,4′-difluorodiphenyl sulfone (SDFDPS) and 4,4′-difluorodiphenyl sulfone (DFDPS) with 4,4′-biphenol (BP) and 1,3-bis-(4-hydroxyphenyl) propenone (BHPP). The content of crosslinkable moieties in the polymer repeat unit is controlled from 0 to 10 mol% by changing the monomer feed ratio of BHPP to BP. The polymer membranes can be crosslinked by irradiating UV with a wavelength of 365 nm. From FT-IR analysis, it can be identified that UV crosslinking mainly occurs due to the combination reaction of radicals that occurs in conjunction with the breaking of the carbon–carbon double bonds (–CH = CH-) of the chalcone moieties in the backbone. Consequently, a new bond is created to form cyclobutane. The crosslinked membranes show less water uptake, a lower level of methanol permeability, and good thermal and mechanical properties compared to pristine (non-crosslinked) membranes while maintaining a reasonable level of proton conductivity. Finally, the fuel cell performance of the crosslinked membranes is comparable to that of the Nafion 115 membrane, demonstrating that these membranes are promising candidates for use as polymer electrolyte membranes in DMFCs.     

Role of post-sulfonation of poly(ether ether sulfone) in proton conductivity and chemical stability of its proton exchange membranes for fuel cell

Commercially available poly(ether ether sulfone), PEES, was directly sulfonated using concentrated sulfuric acid at low temperatures by minimizing degradation during sulfonation. The sulfonation reaction was performed in the temperature range of 5–25 °C. Sulfonated polymers were characterized by FTIR, ¹H NMR spectroscopy and ion exchange capacity (IEC) measurements. Degradation during sulfonation was investigated by measuring intrinsic viscosity, glass transition temperature and thermal decomposition temperature of sulfonated polymers. Sulfonated PEES, SPEES, membranes were prepared by solvent casting method and characterized in terms of IEC, proton conductivity and water uptake. The effect of sulfonation conditions on chemical stability of membranes was also investigated via Fenton test. Optimum sulfonation condition was determined to be 10 °C with conc. H₂SO₄ based on the characteristics of sulfonated polymers and also the chemical stability of their membranes. SPEES membranes exhibited proton conductivity up to 185.8 mS cm⁻¹ which is higher than that of Nafion 117 (133.3 mS cm⁻¹) measured at 80 °C and relative humidity 100%.     

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.     

Preparation and characterization of sulfonated amine-poly(ether sulfone)s for proton exchange membrane fuel cell

Sulfonated amine-poly(ether sulfone)s (S-APES)s were prepared by nitration, reduction and sulfonation of poly(ether sulfone) (ultrason^®-S6010). Poly(ether sulfone) was reacted with ammonium nitrate and trifluoroacetic anhydride to produce the nitrated poly(ether sulfone), and was followed by reduction using tin(II)chloride and sodium iodide as reducing agents to give the amino-poly(ether sulfone). The S-APES was obtained by reaction of 1,3-propanesultone and the amino-poly(ether sulfone) (NH₂-PES) with sodium methoxide. The different degrees of nitration and reduction of poly(ether sulfone) were successfully synthesized by an optimized process. The reduction of nitro group to amino was done quantitatively, and this controlled the contents of the sulfonic acid group. The films were converted from salt to acid forms with dilute hydrochloric acid. Different contents of sulfonated unit of the S-APES were studied by FT-IR, ¹H NMR spectroscopy, differential scanning calorimetry (DSC), and thermo gravimetric analysis (TGA). Sorption experiments were conducted to observe the interaction of sulfonated polymers with water and methanol. The ion exchange capacity (IEC), a measure of proton conductivity, was evaluated. The S-APES membranes exhibit conductivities (25 °C) from 1.05 × 10⁻³ to 4.83 × 10⁻³ S/cm, water swell from 30.25 to 66.50%, IEC from 0.38 to 0.82 meq/g, and methanol diffusion coefficients from 3.10 × 10⁻⁷ to 4.82 × 10⁻⁷ cm²/S at 25 °C.     

Synthesis and characterization of sulfonated poly (arylene ether ketone sulfone) block copolymers containing multi-phenyl for PEMFC

Sulfonated multi-block copolymers (SMBPs) were successfully synthesized from precursors of hydrophilic and hydrophobic block oligomers. The hydrophilic block oligomer was synthesized using 1,2-bis(4-fluorobenzoyl)-3,4,5,6-tetraphenylbenzene (BFBTPB) and 4,4′-(2,2-diphenylethenylidene) diphenol (DHTPE). The hydrophobic block oligomer was prepared by bis(4-hydroxyphenyl) sulfone and bis(4-fluorophenyl) sulfone. The sulfonation was taken selectively on hydrophilic block segment as well as para position of the pendant phenyl groups with concentrated sulfuric acid. To control the IEC the stoichiometry mole ratios were changed with hydrophilic blocks of 10, 13 and 17 mol%. The structural properties of SMBPs were studied by FT-IR, ¹H NMR spectroscopy, thermogravimetric analysis (TGA), and atomic force microscope (AFM). The water uptakes were 9.7–42.3% at 30 °C and 14.3%–70.4% at 80 °C with changing the ion exchange capacities. The resulted ion exchange capacities (IEC) were 1.09–1.63 meq./g. The highest power density of a fuel cell using SMBP 17 (IEC = 1.63 meq./g) and Nafion 211 was 0.41 and 0.45 W/cm², respectively, at 0.6 V.     

Sulfonated poly(ether sulfone) electrolytes structured with mesonaphthobifluorene graphene moiety for PEMFC

Sulfonated poly(ether sulfone)s containing a mixture of cis and trans mesonaphthobifluorene moiety were synthesized, and their properties were characterized. The mesonaphthobifluorene graphene moiety contained 6 phenyl rings and was conjugated together to form planar sheets of sp²-bonded carbon. Poly(arylene ether sulfone)s containing a mixture of cis and trans tetraphenyl ethylene units were synthesized by polycondensation, and converted into graphene by intramolecular Friedel–Craft cyclization with Lewis acid (FeCl₃). The sulfonation was taken selectively on mesonaphthobifluorene units with concentrated sulfuric acid. The structural properties of the sulfonated polymers were investigated by ¹H NMR spectroscopy. The membranes were studied with regard to ion exchange capacity (IEC), water uptake, and proton conductivity.     

Partly fluorinated poly(arylene ether ketone sulfone) hydrophilic–hydrophobic multiblock copolymers for fuel cell membranes

Hydrophilic–hydrophobic alternating poly(arylene ether ketone sulfone) multiblock copolymers, 6FK-BPSH100, were prepared by the synthesis and coupling of partly fluorinated hydrophobic poly(arylene ether ketone)oligomers (6FK) and disulfonated hydrophilic poly(arylene ether sulfone) telechelic oligomers (BPSH100), containing 3,3′-disulfonated-4,4′dichlorodiphenylsulfone (SDCDPS) as a source of ionomeric moieties. By precisely controlling the molecular weight and composition of the telechelic oligomers, a series of multiblock copolymers were prepared varying in block length and ion exchange capacity (IEC) for a comparative study. The resulting copolymers afforded tough and ductile membranes by solution casting from DMAc. Membrane properties of these copolymers were characterized with regard tointrinsic viscosity, thermal stabilities, morphology, water uptake, and proton conductivity. The results were compared to those of Nafion^® and random copolymer BPSH35. The nanophase separated morphology developed in the membranes was illustrated by transmission electron microscopy (TEM), which account for enhanced proton conductivity at reduced relative humidity (RH). More importantly, film processing studies have demonstrated that a major advance in proton conductivity versus RH behavior and greatly reduced water uptake could be achieved via precise annealing experiments.     

Robust proton exchange membrane for vanadium redox flow batteries reinforced by silica-encapsulated nanocellulose

High ion selectivity and mechanical strength are critical properties for proton exchange membranes in vanadium redox flow batteries. In this work, a novel sulfonated poly(ether sulfone) hybrid membrane reinforced by core-shell structured nanocellulose (CNC-SPES) is prepared to obtain a robust and high-performance proton exchange membrane for vanadium redox flow batteries. Membrane morphology, proton conductivity, vanadium permeability and tensile strength are investigated. Single cell tests at a range of 40–140 mA cm⁻² are carried out. The performance of the sulfonated poly(ether sulfone) membrane reinforced by pristine nanocellulose (NC-SPES) and Nafion® 212 membranes are also studied for comparison. The results show that, with the incorporation of silica-encapsulated nanocellulose, the membrane exhibits outstanding mechanical strength of 54.5 MPa and high energy efficiency above 82% at 100 mA cm⁻², which is stable during 200 charge-discharge cycles.     

Construction of a new continuous proton transport channel through a covalent crosslinking reaction between carboxyl and amino groups

Sulfonated poly(arylene ether ketone sulfone) bearing pendant carboxylic acid groups (C-SPAEKS) and sulfonated poly(arylene ether ketone sulfone) containing amino groups (Am-SPAEKS) were used to prepare C-SPAEKS/Am-SPAEKS crosslinked membranes. ¹H NMR and Fourier transform infrared spectra proved that C-SPAEKS and Am-SPAEKS copolymers, as well as C-SPAEKS/Am-SPAEKS crosslinked membrane, were successfully synthesized. TEM images showed that a continuous proton transport channel formed after crosslinking. Thermogravimetric analysis curves demonstrated that the thermal property of the crosslinked membranes improved. The crosslinked membranes exhibited suitable mechanical properties at 25 and 80 °C. The methanol permeability of C-SPAEKS/Am-SPAEKS-40 was 2.35 × 10⁻⁷ cm² s⁻¹ at 60 °C, which was lower than that of C-SPAEKS (24.12 × 10⁻⁷ cm² s⁻¹) and Am-SPAEKS (17.91 × 10⁻⁷ cm² s⁻¹). The proton conductivity of C-SPAEKS/Am-SPAEKS-40 was 0.089 S cm⁻¹, which was higher than that of C-SPAEKS and Am-SPAEKS at 80 °C. The results proved that C-SPAEKS/Am-SPAEKS crosslinked membranes were potential proton exchange membranes for direct methanol fuel cell applications.     

Crosslinked sulfonated poly(arylene ether sulfone)/silica hybrid membranes for high temperature proton exchange membrane fuel cells

Sulfonated poly(arylene ether sulfone) copolymer is synthesized via nucleophilic step polymerization of sulfonated 4,4′-dichlorodiphenyl sulfone, 4,4′-dichlorodiphenyl sulfone and phenolphthalin monomers in the presence of potassium carbonate. The copolymer is blended with various amounts of silica particles to form organic–inorganic composite membranes. Esterification reaction is carried out between silica particles and the sulfonated polymer chains by thermal treatment in the presence of sodium hypophosphite, which catalyzed the esterification reaction. The composition and incorporation of the sulfonated repeat unit are confirmed by ¹H NMR. The water uptake, proton conductivity, and thermal decomposition temperature of the membranes are measured. The silica content in the polymer matrix and the effect of esterification are evaluated. All composite membranes show better water uptake and proton conductivity than the unmodified membrane. Moreover, the membranes are tested in a commercial single cell at 80 °C and 120 °C in humidified H₂/air under different relative humidity conditions. The composite membrane containing 10% (w/w) silica shows the best performance among the prepared membranes especially under high temperature and low humidity conditions.