Synthesis of nickel catalyzed sulfonated poly (phenylenebenzophenone)s from primarily sulfonated monomer for proton exchange membranes

This extensive study adequately explores the considerable influence of nickel catalyst and wholly aromatic primarily sulfonated monomers. The synthesis of the chemically and mechanically stable sulfonated poly (phenylenebenzophenone)s (SPPBP) flexible membranes from primarily Sulfonated 1,4-dichloro-2,5-diphenylenebenzophenone (SPBP) and 1,4-dichloro-2,5-diphenylenemethoxybenzophenone (SPMBP) monomers have been reported here using nickel catalyzed carbon-carbon coupling copolymerization. The synthesized SPBP monomer typically possesses a symmetrical structure with excellent reactivity that effectively assisted to control the position, number, and distribution of the sulfonic acid groups in the polymer backbone and attained high molecular weight SPPBP copolymers. The synthesized polymers showed ion exchange capacity (IEC) 1.0–1.93 meqv./g, water uptake 36.4–84.7% and comparable proton conductivity 28.5–94.9 meqv./g to Nafion^® (98.92 meqv./g) at 90 °C. The atomic force microscopic (AFM) results show that SPPBP copolymer membranes provide well phase-separated morphology and thermogravimetric analysis (TGA) confirms the excellent thermal stability of the synthesized SPPBP membranes as well. The synthesized SPPBP membranes possess a potential feature for the practical application in the fuel cell.     

Studies of sulfonated poly(phenylene)-block-poly(ethersulfone) for proton exchange membrane fuel cell

The polymers were prepared by nickel catalyzed carbon–carbon coupling reaction of 1,4-dichloro-2,5-dibenzoylbenzene (DCDBB) and sulfone oligomer. DCDBB was synthesized from oxidation reaction of 2,5-dichloro-p-xylene and followed by Friedel–Craft reaction with benzene. DCDBB monomer had good reactivity in polymerization by electron withdrawing group as benzophenone. Sulfone group of oligomer had improving flexibility and solubility. Post sulfonation was carried out to add sulfonic acid groups by using chlorosulfuric acid. These polymers were presumably stable against nucleophilic attack by hydrogen peroxide, hydroxide anion, and radical generated by proton exchange membrane fuel cell operation system. The number of sulfonic acid groups were controlled by varying the mole ratio of 1,4-dichloro-2,5-dibenzoylbenzene in synthesized polymer. A series of membranes were studied by ¹H NMR spectroscopy, thermo-gravimetric analysis, ion exchange capacity, water uptake, and proton conductivity. Also surface morphologies were assessed by atomic force microscope (AFM).     

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.     

Preparation and characterization of grafted propane sulfonic acid polyphenylene membrane via superacid-catalyzed reaction

A series of polyphenylene-based polyelectrolytes were synthesized from 2,2'-biphenol, and isatin by superacid catalyzed polyhydroxyalkylation reactions. Grafted sulfonated polyphenylenes were synthesized via K₂CO₃ catalyzed condensation reaction with 3-bromopropane sulfonic acid potassium salt. These polymers have all carbon–carbon linkages without any ether linkage on polymer backbone, which were not attacked by nucleophiles (H₂O, hydrogen peroxide, hydroxide anion and radical). Particularly, chemical modification to flexible sulfoalkyl groups implanted to a biphenol unit afforded better stability due to less reactive towards nucleophilic substitution reaction, and good proton mobility because of well phase separation. The structural properties of the synthesized polymers were investigated by ¹H NMR spectroscopy. The membranes were studied by ion exchange capacity (IEC), water uptake, dimensional stability as well as proton conductivity assessment. The chemical degradation test was performed by Fenton's reagent, and compared with the usual sulfonated poly(ether sulfone)s and Nafion.     

Preparation,characterization and properties of proton exchange nanocomposite membranes based on poly(vinyl alcohol) and poly(sulfonic acid)-grafted silica nanoparticles

Nanocomposite membranes based on the poly(vinyl alcohol) (PVA)/poly(sulfonic acid)-grafted silica nanoparticles (PSA-g-SN) were prepared via solvent casting of PVA cross linked by glutardialdehyde in the presence of various amounts (0–20 wt%) of silica nanoparticles (SN), poly(styrene sulfonic acid)- (PSSA-g-SN) and poly (2-acrylamido-2-methyl-1-propane sulfonic acid)-grafted silica nanoparticles (PAMPS-g-SN) as hydrophilic inorganic modifiers. PSA-g-SN nanoparticles were synthesized by surface-initiated redox grafting of SSA and AMPS monomers from the surface of the aminopropylated silica nanoparticles. Membranes were then characterized by FTIR, impedance spectroscopy, thermogravimetric analysis (TGA), water uptake, tensile strength test and SEM. The best proton conductivity was observed for membranes containing 5 wt% of nanoparticles. Among three nanoparticles used, the highest proton conductivity (10.4 mS/cm) was observed for PVA membrane prepared in the presence of 5 wt% PAMPS-g-SN nanoparticles. Results showed that grafting of sulfonated monomer onto the silica nanoparticles enhances various properties, for example proton conductivity, of the polymer electrolyte membranes (PEMs).     

Synthesis and characterization of sulfonated poly(arylene ether ketone ketone sulfone) membranes for application in proton exchange membrane fuel cells

A series of sulfonated poly(arylene ether ketone ketone sulfone) (SPAEKKS) copolymers were synthesized by nucleophilic polycondensation. The copolymers exhibit good thermal and oxidative stabilities, all the SPAEKKS copolymers can be cast into tough membranes. Ionic exchange capacities (IEC), water uptake properties, thermal stabilities, methanol diffusion coefficients and proton conductivities were thoroughly studied. Also the microstructures of the membranes were investigated by TEM. The proton conductivity of the SPAEKKS-4 membrane is close to that of Nafion-117 at 80 °C. The methanol diffusion coefficient of the membrane is much lower than that of Nafion-117 under the same testing conditions. The SPAEKKS membranes are promising in proton exchange membranes fuel cell (PEMFC) application.     

Synthesis and characterization of proton exchange membranes based on sulfonated poly(fluorenyl ether nitrile oxynaphthalate) for direct methanol fuel cells

A series of sulfonated poly(fluorenyl ether nitrile oxynaphthalate) (SPFENO) copolymers with different degree of sulfonation (DS) are synthesized via nucleophilic polycondensation reactions with commercially available monomers. Incorporation of the naphthalanesulfonate group into the copolymers and their copolymer structures are confirmed by ¹H NMR spectroscopy. Thermal stability, mechanical properties, water uptake, swelling behavior, proton conductivity and methanol permeability of the SPFENO membranes are investigated with respect to their structures. The electrochemical performance of a direct methanol fuel cell (DMFC) assembled with the SPFENO membrane was evaluated and compared to a DMFC with a Nafion 117 membrane. The DMFC assembled with the SPFENO membrane of proper DS exhibits better electrochemical performance compared to the Nafion 117-based cell.     

Synthesis and characterization of new proton conducting hybrid membranes for PEM fuel cells based on poly(vinyl alcohol) and nanoporous silica containing phenyl sulfonic acid

Organic-inorganic hybrid proton exchange membranes were prepared from poly(vinyl alcohol) (PVA) and various amounts of nanoporous silica containing phenyl sulfonic acid groups. These hybrid membranes were prepared via co-condensation of functionalized nanoporous SBA-15 (SBA-ph-SO₃H) as hydrophilic inorganic modifier, glutaraldehyde (GLA) as cross-linking agent in a PVA matrix. These membranes were characterized for their morphology, thermal stability, electrochemical and physicochemical properties using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and water uptake studies. The SBA-ph-SO₃H/PVA composite membranes have a higher water retention and thermal stability than that of Nafion 117, perhaps because of responsibility of both acidic groups and nanoporous structure of silica additive. This work demonstrates the promising potential of new composite membranes for the development of high-performance and high-stability PEM fuel cells with improved proton conductivity.     

Synthesis and characterization of sulfonated polyphenylene containing DCTPE for PEMFC potential application

The synthesis of conjugated polyphenylenes containing tetraphenylethylene (PPTPE) moiety, their functionalization with sulfonic acid groups, and the measurement of apposite parameters for PEMs are described. The polymers were prepared by Ni-catalyzed carbon–carbon coupling reaction of dichlorotetraphenylethylene and 2,5-dichlorobenzophenone. These polymers have all carbon–carbon linkages without any ether linkage on polymer backbone, which were not attacked by nucleophiles (H₂O, hydrogen peroxide, hydroxide anion and radical), and the twisted structure provided good solubility in aprotic polar solvent. The sulfonic acid groups were introduced by sulfonation reaction with concentrated sulfuric acid. All these membranes were prepared from dimethylacetamide (DMAc) polymer solution. The membranes were studied by ion exchange capacity (IEC), water uptake, proton conductivity, and single cell performance. The chemical degradation test of the prepared membrane was performed by Fenton reagent, and compared with normal sulfonated poly(ether sulfone)s & Nafion.     

Crosslinked poly(arylene ether sulfone) block copolymers containing quinoxaline crosslinkage and pendant butanesulfonic acid groups as proton exchange membranes

Crosslinkable poly (arylene ether sulfone) block copolymers (bSPAES (x/y)) containing pendant butanesulfonic acid and ethanedione groups were prepared from a new side-chain difluoro aromatic monomer 1-(2,6-difluorophenyl)-2-(3,5-dimethoxyphenyl)-1,2-ethanedione via block copolycondensation, demethylation, and further nucleophilic substitution of 1,4-butane sultone. Meanwhile, quinoxaline-based crosslinked block copolymers (C-bSPAES (x/y)) were obtained via cyclocondensation. The corresponding block copolymer membranes have high mechanical properties and anisotropic membrane swelling for either crosslinked or uncrosslinked ones. bSPAES (5/10) with ion exchange capacity (IEC) of 2.05 mequiv. g⁻¹ has low water uptake (WU) of 59.1% at 80 °C but relatively high conductivity of 225 mS cm⁻¹, which is ascribed to its good microphase separation. Meanwhile, the crosslinked C-bSPAES (5/10) with IEC of 1.76 mequiv. g⁻¹ exhibits a decreased WU by half, an improved oxidative stability by 200% and a reduced membrane swelling by 40% than the uncrosslinked bSPAES (5/10). The results suggest that quinoxaline-based crosslinking can obviously improve properties of bSPAES (x/y). In addition, even though maximum power density of C-bSPAES (5/10) is lower than that of Nafion 212, C-bSPAES (5/10) still has an acceptable good single-cell performance, indicating a possible fuel cell application.     

Synthesis and characterization of pendant propane sulfonic acid on phenylene based copolymers by superacid-catalyzed reaction

A series of phenylene based polyelectrolytes were synthesized from 2,2′-biphenol, biphenyl and isatin by superacid catalyzed polyhydroxyalkylation reactions. Grafted sulfonated polymers were synthesized by substitution reaction with 3-bromopropane sulfonic acid potassium salt. These polymers have all carbon–carbon structure on polymer backbone without ether linkage. Particularly, the flexible sulfoalkyl groups were attached to a 2,2′-biphenol unit and formed grafting structure which afforded better stability due to less reactive towards nucleophilic substitution reaction, and good proton mobility because of well phase separation. The structure properties of the synthesized polymers were investigated by ¹H NMR spectroscopy. The membranes were studied by ion exchange capacity (IEC), water uptake, dimensional stability, proton conductivity, and cell performance. The chemical deterioration test was performed by Fenton reagent, and compared with normal sulfonated poly(ether sulfone)s and Nafion.     

Synthesis and characterization of novel sulfonated poly(arylene ether ketone) copolymers with pendant carboxylic acid groups for proton exchange membranes

A series of novel side-chain-type sulfonated poly(arylene ether ketone)s with pendant carboxylic acid groups copolymers (C-SPAEKs) were synthesized by direct copolymerization of sodium 5,5′-carbonyl-bis(2-fluorobenzenesulfonate), 4,4′-difluorobenzophenone and 4,4′-bis(4-hydroxyphenyl) valeric acid (DPA). The expected structure of the sulfonated copolymers was confirmed by FT-IR and ¹H NMR. Membranes with good thermal and mechanical stability could be obtained by solvent cast process. It should be noted that the proton conductivity of these copolymers with high sulfonatation degree (DS > 0.6) was higher than 0.03 S cm⁻¹ and increased with increasing temperature. At 80 °C, the conductivity of C-SPAEK-3 (DS = 0.6) and C-SPAEK-4 (DS = 0.8) reached up to 0.12 and 0.16 S cm⁻¹, respectively, which were higher than that of Nafion 117 (0.10 S cm⁻¹). Moreover, their methanol permeability was much lower than that of Nafion 117. These results showed that the synthesized materials might have potential applications as the proton exchange membranes for DMFCs.     

Synthesis and electrochemical properties of blend membranes of polysulfone and poly (acrylic acid-co-2-(2-(piperazin-1-yl) ethylamino)-2-hydroxyethyl methacrylate) for proton exchange membrane fuel cell

In this work, new piperazine containing copolymer membrane was developed from acrylic acid and 2-(2-(piperazin-1-yl)ethylamino)-2-hydroxyethyl methacrylate through free radical polymerization method by means of AIBN as an initiator, in bulk. The monomer feed ratio was varied to obtain various copolymers having a different composition. The developed copolymer was blended in polysulfone (PSF) at 3 and 6 wt% using N,N′-Dimethylformamide solvent. The FTIR spectra and 1H NMR spectral data have proved the presence of copolymer that has hydrophilic functional group which influences the better proton conductivity. The membranes were characterized by their morphology using scanning electron microscope and x-ray diffraction analysis. The hydrophilic nature of the membranes is proved through high water uptake ratio. The exchangeable proton at the carboxylic acid group has enhanced the high ion exchange capacity. The blend membranes have higher water uptake, low swelling rate and higher ion exchange capacity than that of neat PSF membrane. The fabrication of fuel cell and studies on proton exchange capacity indicates that the prepared membranes have proton conductivity of as high as 8.77 × 10^?4 S cm^?1. Low methanol crossover was obtained about 2.112 × 10^?6 cm²s^?1 when compared to the pristine membrane.     

Novel sulfonated poly(oxybenzimidazole) membranes bearing sulfo-napthalimide pendant groups with improved proton conductivity and fuel cell performance

The goal of the present work is to introduce a new aromatic bulky six-membered sulfo-napthalimide pendant groups, specifically 2-(2,5-dicarb-oxyphenyl-1,3-dioxo- 2,3-didihydro-1Hbenzo[de]isoquinoline-6-sulfonate (PDDDBIS), into the poly(oxybenzimidazole) (POBI) main chain. As no sulfo-napthalimide-bearing POBI has been reported yet, this could be a potential strategy to improve the solubility, processability, and proton conductivity of sulfonated POBIs in addition to boosting fuel cell performance. Out of six membranes synthesized, one sulfonated POBI membrane with pendant PDDDBIS groups (SPOBI-100) exhibited a fairly high proton conductivity of 0.172 S/cm, which is higher than Nafion-117 (0.161 S/cm) at 90 °C. Notably, an H₂/O₂ PEM fuel cell fabricated with the SPOBI-100 membrane displayed good performance with the maximum peak power density of 547 mW/cm² and output current density of 1259 mA/cm² in 0.99 V at 90 °C with100% RH, which is higher than the Nafion 117 power density (519 mW/cm²) and current density (1215 mA/cm²) under the same testing conditions.     

Controllable sulfonation of aromatic poly(arylene ether ketone)s containing different pendant phenyl rings

The sulfonation selectivity of various pendant phenyl groups in poly(arylene ether ketone) (Ph-3F-PAEK) is invested via the postsulfonation approach. The sulfonated Ph-3F-PAEKs with different degrees of sulfonation (DS) are quantitatively synthesized by controlling the length of the segments that cannot be sulfonated. In this study, ¹H NMR and FT-IR are used to confirmed the structures of the polymers and the experimentally DS values were calculated by ¹H NMR. The experimentally observed DSs are corresponding to the theoretical values expected from the monomer ratios. All the sulfonated membranes have excellent mechanical properties (with a Young's modulus >1.3 GPa, a tensile strength >55 MPa and the elongation >10%). Thermogravimetric analysis (TGA) is used to characterized the thermal stability of these polymers, and all the polymers show excellent thermal properties at high temperatures. The methanol permeability values of Ph-3F-SPAEKs in the range of 0.37 × 10⁻⁷ cm² s⁻¹ to 4.12 × 10⁻⁷ cm² s⁻¹ are much lower than that of Nafion^® 117 (1.55 × 10⁻⁶ cm² s⁻¹). It should be noted that the polymer with highest DS, Ph-3F-SPAEK-100 with an ion exchange capacity of 2.16 mequiv. g⁻¹, exhibits high proton conductivity of 0.187 S cm⁻¹ at 80 °C, which is also higher than that of Nafion^® 117.     

Synthesis of sulfonated poly(diketonephenylene)s containing dibenzoyl moiety via Ni/Zn catalyst

The new monomer, 1,2-bis(4-chlorobenzoyl)-3,6-diphenylbenzene, was synthesized from the Frieldel–Craft reaction of chlorobenzene and fumaryl chloride followed by the Diels–Alder reaction. Poly(diketonephenylene)s containing the dibenzoyl moiety in the side chains were synthesized from 1,2-bis(4-chlorobenzoyl)-3,6-diphenylbenzene and 1,4-dichloro-2,5-dibenzoylbenzene as a reactive monomer. The polymerization was performed employing a Ni/Zn catalyzed carbon–carbon coupling reaction followed by a sulfonation reaction with chlorosulfuric acid. These polymers consisted of diketone in the main chain and dibenzoyl in the side chain, which consisted of four active phenyl groups for sulfonation. A series of membranes was studied via ¹H NMR spectroscopy, ion exchange capacity (IEC), water uptake, and proton conductivity analyses. The thermal and chemical stability of the prepared membrane is then characterized through a thermogravimetric investigation.     

Sulfonated poly(arylene ether)s based proton exchange membranes for fuel cells

During the past decade proton exchange membrane fuel cells (PEMFCs) as one kind of the potential clean energy sources for electric vehicles and portable electronic devices are attracting more and more attentions. Although Nafion® membranes are considered as the benchmark of proton exchange membranes (PEMs), the drawbacks of Nafion® membranes restrict the commercialization in the practical application of PEMFCs. As of today, the attention is to focus on developing both high-performance and low-cost PEMs to replace Nafion® membranes. In all of these PEMs, sulfonated poly(arylene ether ketone)s (SPAEKs) and sulfonated poly(arylene ether sulfone)s (SPAESs) are the most promising candidates due to their excellent performance and low price. In this review, the efforts of SPAEK and SPAES membranes are classified and introduced according to the chemical compositions, the microstructures and configurations, as well as the composites with polymers and/or inorganic fillers. Specifically, several perspectives related to the modification and composition of SPAESs and SPAEKs are proposed, aiming to provide the development progress and the promising research directions in this field.     

Poly(arylene ether)s with pendant sulfoalkoxy groups prepared by direct copolymerization method for proton exchange membranes

A novel sulfonated monomer sodium-3-(4-(2,6-difluorobenzoyl)phenoxy)propane-1-sulfonate was designed and synthesized. Based on above monomer, a series of sulfonated poly(arylene ether) copolymers containing aliphatic acid groups between aromatic backbones and sulfonic acid groups (PSOA-SPAE) were successfully prepared by direct copolymerization. Ion exchange capacity (IEC) of the copolymers could be mediated in the range of 1.07–1.61 meq g⁻¹ by the monomer ratios used in the copolymerization. These copolymers exhibited good oxidative and dimensional stability. The proton conductivities of copolymer films increased with the increase of IEC and temperature. The conductivity of PSOA-SPAE-80 was 4.94 × 10⁻² S cm⁻¹ at room temperature, and was up to 1.35 × 10⁻¹ S cm⁻¹ at 100 °C, which was close to that of Nafion 117. These copolymers may be promising proton exchange membranes (PEMs) due to their high proton conductivity and good oxidative and dimensional stability.     

Novel sulfonated poly(arylene ether ketone) copolymers bearing carboxylic or benzimidazole pendant groups for proton exchange membranes

A novel strategy in which the benzimidazole group and sulfonic group are simultaneously attached to an aromatic polymer has been reported in this paper. For this purpose, sulfonated poly(arylene ether ketone) copolymers containing carboxylic acid groups (SPAEK-x-COOH, x refers to the molar percentage of sulfonated repeating units) are prepared by the aromatic nucleophilic polycondensation of sodium 5,5′-carbonyl-bis(2-fluobenzene-sulfonate) (SDFBP), 4,4′-difluorobenzophenone (DFBP) and phenolphthalin (PPL). Then the carboxylic acid groups attached to the SPAEK-x-COOH are transformed to benzimidazole units through condensation reactions (referred to as SPAEK-x-BI). Fourier transform infrared spectroscopy and ¹H NMR measurements are used to characterize and confirm the structures of these copolymers. SPAEK-x-COOH membranes exhibit superior mechanical properties with maximum elongations at break up to 133%, meanwhile SPAEK-x-BI also shows good thermal and mechanical stability. The proton conductivity, swelling ratio and methanol permeability of the polymers with benzimidazole are lower than those with carboxylic groups, which indicated that there is an acid-base complex between benzimidazole and sulfonic acid groups. A balance of proton conductivity, methanol permeability, thermal and mechanical stabilities can be designed by incorporation of functional groups to meet the requirements for the applications in direct methanol fuel cells.