Quinoxaline-based crosslinked membranes of sulfonated poly(arylene ether sulfone)s for fuel cell applications

A series of crosslinkable sulfonated poly(arylene ether sulfone)s (SPAESs) were synthesized by copolymerization of 4,4′-biphenol with 2,6-difluorobenzil and 3,3′-disulfonated-4,4′-difluorodiphenyl sulfone disodium salt. Quinoxaline-based crosslinked SPAESs were prepared via the cyclocondensation reaction of benzil moieties in polymer chain with 3,3′-diaminobenzidine to form quinoxaline groups acting as covalent and acid-base ionic crosslinking. The uncrosslinked and crosslinked SPAES membranes showed high mechanical properties and the isotropic membrane swelling, while the later became insoluble in tested polar aprotic solvents. The crosslinking significantly improved the membrane performance, i.e., the crosslinked membranes had the lower membrane dimensional change, lower methanol permeability and higher oxidative stability than the corresponding precursor membranes, with keeping the reasonably high proton conductivity. The crosslinked membrane (CS1-2) with measured ion exchange capacity of 1.53 mequiv. g⁻¹ showed a reasonably high proton conductivity of 107 mS/cm with water uptake of 48 wt.% at 80 °C, and exhibited a low methanol permeability of 2.3 × 10⁻⁷ cm² s⁻¹ for 32 wt.% methanol solution at 25 °C. The crosslinked SPAES membranes have potential for PEFC and DMFCs.     

Synthesis and characterization of crosslinked sulfonated poly(arylene ether sulfone) membranes for high temperature PEMFC applications

Sulfonated poly(arylene ether sulfone) copolymers containing carboxyl groups are prepared by an aromatic substitution polymerization reaction using phenolphthalin, 3,3′-disulfonated-4,4′-dichlorodiphenyl sulfone, 4,4′-dichlorodiphenyl sulfone and 4,4′-bisphenol A as polymer electrolyte membranes for the development of high temperature polymer electrolyte membrane fuel cells. Thin, ductile films are fabricated by the solution casting method, which resulted in membranes with a thickness of approximately 50 μm. Hydroquinone is used to crosslink the prepared copolymer in the presence of the catalyst, sodium hypophosphite. The synthesized copolymers and membranes are characterized by ¹H NMR, FT-IR, TGA, ion exchange capacity, water uptake and proton conductivity measurements. The water uptake and proton conductivity of the membranes are decreased with increasing the degree of crosslinking which is determined by phenolphthalin content in the copolymer (0-15 mol%). The prepared membranes are tested in a 9 cm² commercial single cell at 80 °C and 120 °C in humidified H₂/air under different relative humidity conditions. The uncrosslinked membrane is found to perform better than the crosslinked membranes at 80 °C; however, the crosslinked membranes perform better at 120 °C. The crosslinked membrane containing 10 mol% of phenolphthalin (CPS-PP10) shows the best performance of 600 mA cm⁻² at 0.6 V and better performance than the commercial Nafion^® 112 (540 mA cm⁻² at 0.6 V) at 120 °C and 30 % RH.     

Synthesis of multi-block poly(arylene ether sulfone) copolymer membrane with pendant quaternary ammonium groups for alkaline fuel cell

A series of multi-block poly(arylene ether sulfone)s are synthesized via the copolymerization of bis(4-hydroxyphenol) sulfone, 3,3′, 5,5′-tetramethylbiphenol and 4,4′-difluorodiphenyl sulfone. The resulting multi-block copolymers are brominated by using N-bromosuccinmide (NBS) as bromination reagent. The bromomethylated copolymer is solution cast to form clear, creasable films, and subsequent soaking of these films in aqueous trimethylamine to give benzyltrimethylammonium groups. The anion exchange membranes obtained by the solution hydroxide exchange with aqueous sodium hydroxide show varying degrees of ionic conductivity depending on their ion exchange capacity. The highest hydroxide conductivity 0.029 S cm⁻¹ is achieved with the QBPES-40 membrane having IEC value of 1.62 mequiv g⁻¹ at room temperature and 100% RH. The obtained anion exchange membranes also have good mechanical properties and dimensional stability, which greatly facilitates the preparation of a MEA and the cell operation.     

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.     

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.     

Crosslinked poly(arylene ether sulfone) block copolymers containing pendant imidazolium groups as both crosslinkage sites and hydroxide conductors for highly selective and stable membranes

Crosslinked poly(arylene ether sulfone)s with pendant imidazolium units, both as crosslinkage sites and hydroxide conductors, were developed as anion exchange membranes (AEMs). These crosslinked membranes, with IECs of 0.80–1.21 meq/g, showed high hydroxide conductivity over 0.01 S/cm at 20 °C and 0.06 S/cm at 80 °C. Furthermore, the crosslinked membranes containing imidazolium groups on the side chains of the polymer exhibited good thermal, mechanical and dimensional stability, as well as excellent chemical stability at high pH. The combination of high hydroxide conductivity and low methanol permeability caused these crosslinked membranes to have very high selectivity up to 13 × 10⁵ S s/cm³, suggesting our crosslinked membranes are suitable for DMAFCs. These membranes can also be used for various other applications including gas separations.     

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.     

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.     

Properties and fuel cell performance of proton exchange membranes prepared from disulfonated poly(sulfide sulfone)

A series of disulfonated poly(sulfide sulfone)s (SPSSF)s copolymers are synthesized via direct aromatic nucleophilic substitution polycondensation of 4,4′-dichlorodiphenylsulfone (DCDPS), 3,3′-disulfonate-4,4′-dichlorodiphenylsulfone (SDCDPS) and 4,4′-thiobisbenzenethiol at various molar ratios. Tough and flexible membranes with 30 mol% (SPSSF30) to 50 mol% (SPSSF50) SDCDPS monomers are obtained by casting from DMAc solution. Their physicochemical properties including thermal properties, mechanical properties, water uptake, swelling ratio and oxidative stability are fully investigated. And the fuel cell performance of SPSSF membranes at different temperature and relative humidity is evaluated comprehensively for the first time. It is found that the SPSSF40 membrane exhibited low dimensional change in the temperature range of 20–100 °C, good mechanical properties, high oxidative stability and comparable fuel cell performance to Nafion 212 membrane. Besides, the H₂ crossover density of the SPSSF40 membrane is only 50% of that of Nafion 212 membrane. Consequently, SPSSF40 membranes prove to be promising candidates as new polymeric electrolyte materials for proton exchange membrane (PEM) fuel cells operated at medium temperatures.     

Preparation and properties of phosphoric acid doped sulfonated poly(tetra phenyl phthalazine ether sulfone) copolymers for high temperature proton exchange membrane application

Phosphoric acid-doped sulfonated poly(tetra phenyl phthalazine ether sulfone) (PA-SPTPPES) copolymers were successfully synthesized by the 4,4′-dihydroxydiphenylsulfone with 1,2-bis(4-fluorobenzoyl)-3,4,5,6-tetraphenylbenzene (BFBTPB) and 4,4′-difluorodiphenylsulfone in sulfolane. Poly(tetra phenyl phthalazine ether sulfone)s (PTPPESs) were prepared via an intramolecular ring-closure reaction of dibenzoylbenzene of precursor and hydrazine. The sulfonated poly(tetra phenyl phthalazine ether sulfone) (SPTPPES) membranes were obtained by sulfonation under concentrated sulfuric acid, and followed phosphoric acid-doped by immersion in phosphoric acid. Different contents of doped and sulfonated unit of PA-SPTPPES (10, 15, 20 mol% of BFBTPB) were studied by FT-IR, ¹H NMR spectroscopy, and thermo gravimetric analysis (TGA). The ion exchange capacity (IEC) and proton conductivity of SPTPPESs and PA-SPTPPESs were evaluated with increase of degree of sulfonation and doping level. The PA-SPTPPESs membranes exhibit proton conductivities (80 °C, relative humidity 30%) of 41.3 ∼ 74.1 mS/cm and the maximum power densities of PA-SPTPPES 10, 15, and 20 were about 294, 350, and 403 mW/cm².     

Crosslinked sulfonated poly(arylene ether ketone) membranes bearing quinoxaline and acid-base complex cross-linkages for fuel cell applications

A series of crosslinkable sulfonated poly(arylene ether ketone)s (SPAEKs) were synthesized by copolymerization of 4,4′-biphenol with 2,6-difluorobenzil and 5,5′-carbonyl-bis(2-fluorobenzene-sulfonate). A facile crosslinking method was successfully developed, based on the cyclocondensation reaction of benzil moieties in polymer chain with 3,3′-diaminobenzidine to form quinoxaline groups acting as covalent and acid-base ionic crosslinking. The uncrosslinked and crosslinked SPAEK membranes showed high mechanical properties and the isotropic membrane swelling, while the later became insoluble in tested polar aprotic solvents. The crosslinking significantly improved the membrane performance, i.e., the crosslinked membranes had the lower membrane dimensional change, lower methanol permeability and higher oxidative stability than the corresponding precursor membranes, with keeping the reasonably high proton conductivity. The crosslinked membrane (C-B4) with an ion exchange capacity of 2.02 mequiv. g⁻¹ showed a reasonably high proton conductivity of 111 mS cm⁻¹ with a low water uptake of 42 wt% at 80 °C. C-B4 exhibited a low methanol permeability of 0.55 × 10⁻⁶ cm² s⁻¹ for 32 wt% methanol solution at 25 °C. The crosslinked SPAEK membranes have potential for PEFC and DMFC applications.     

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^®.     

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.     

Comparison of alkaline fuel cell membranes of random & block poly(arylene ether sulfone) copolymers containing tetra quaternary ammonium hydroxides

A series of modified anion conductive block poly(arylene ether sulfone) copolymer membranes containing a selective substituted unit, 15%, 20% and 25% 4,4′-(2,2-diphenylethenylidene) diphenol, were prepared for use in alkaline fuel cells. The anion exchange membranes were synthesized by first introducing chloromethyl groups. Quaternary ammonium groups could then be added to the tetra-phenyl ethylene units, followed by subsequent ion exchange. The tetra quaternary ammonium hydroxide polymers showed high molecular weights and exhibited high solubility in polar aprotic solvents. The block copolymer membrane showed higher ionic conductivity (21.37 mS cm⁻¹) than the random polymer membrane of similar composition (17.91 mS cm⁻¹). The membranes showed good chemical stability in 1.0 M KOH solution at 60 °C. They were characterized by ¹H NMR, FT-IR, TGA and measurements of ion exchange capacity, water uptake and ionic conductivity.     

Soluble sulfonated polybenzothiazoles derived from 3,3′-disulfonate-4,4′-dicarboxylbiphenyl for proton exchange membranes

Two series of sulfonated polybenzothiazoles were synthesized by polycondensation of 2,5-diamino-1,4-benzenedithiol dihydrochloride and 3,3′-disulfonate-4,4′-dicarboxylbiphenyl with 4,4′-dicarboxylbiphenyl or 2,2-bis(4-carboxyphenyl) hexafluoropropane, which were termed as sPBT-DP and sPBT-BP, respectively. The first series is insoluble in common polar solvents because of its rigid structure. In contrast, the sPBT-BP series are soluble in DMSO and NMP, due to the flexible hexafluoroisopropylidene moieties in the backbone. Thus they could be cast into homogeneous membrane and evaluated as proton exchange membranes. The studies illustrated that they showed high thermal and oxidative stability as well as excellent mechanical properties. Moreover, they exhibited high proton conductivity and outstanding dimensional stability. For example, sPBT-BP57.5 displayed a proton conductivity of 0.094 S/cm and an in-plane swelling of 9.7% as well as a through-plane swelling of 35% at 80 °C. The sPBT-BP ionomers are a promising material for proton exchange membranes.     

4,4′-Oxydianiline (ODA) containing sulfonated polyimide/protic ionic liquid composite membranes for anhydrous proton conduction

The aim of this study was to utilize ionic liquids (ILs) in preparation of modified sulfonated polyimide (SPI) composite membranes to substantially increase the conductivity of proton exchange membranes (PEMs). Protic ILs used included 1-vinylimidazolium trifluoromethanesulfonate [ImVH][OTf] and 1-methyl-imidazolium trifluoromethanesulfonate [ImMH][OTf]. SPIs are synthesized from diamine, 2,2-bis[4-(4-amino-phenoxy)phenyl]propane (BAPP), sulfonated diamine, 4,4′-diamino diphenyl ether-2,2′-disulfonic acid (ODADS), and an aromatic anhydride, ODPA (4,4′-oxy diphthalic anhydride). ODADS improves conductivity, while BAPP enhances the mechanical and thermal properties of SPIs. We have prepared SPI/IL composite PEM using 50 wt.% [ImVH][OTf] with a high conductivity of 3–6 mS/cm at 120 °C and anhydrous condition depending on the ODADS content. [ImVH][OTf] offered better conductivity, which can be attributed to its chemical structure that has a vinyl group attached to an imidazolium ring to provide lower melting temperature and lattice energy, thereby increasing conductivity.     

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.     

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.     

Proton exchange membranes based on semi-interpenetrating polymer networks of fluorine-containing polyimide and Nafion

A series of reinforced composite membranes as proton exchange membranes were prepared from Nafion^®212 and crosslinkable fluorine-containing polyimides (FPI). FPI was prepared from the polymerization of 4,4′-(hexafluoroisopropylidene) diphthalic anhydride (6FDA), 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl (TFMB), and 3,5-diaminobenzoic acid (DABA). Then FPI was thermally crosslinked during the membrane preparation and formed the semi-interpenetrating polymer networks (semi-IPN) structure in the composite membranes. The thermal properties of the composite membranes were characterized by thermogravimetric analysis. The crosslinking density of FPI in the composite membranes was evaluated by the gel fraction. These membranes showed excellent thermal stabilities and good oxidative stabilities. Compared with Nafion^®212, the obtained composite membranes displayed much improved mechanical properties and dimensional stabilities. The tensile strength of the composite membranes was more than twice that of Nafion^®212. The composite membranes exhibited high proton conductivity, which ranged from 2.3 × 10⁻² S cm⁻¹ to 9.1 × 10⁻² S cm⁻¹. All membranes showed an increase in proton conductivity with temperature elevation.     

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.