Highly proton conducting proton‐exchange membranes based on fluorinated poly(arylene ether ketone)s with octasulfonated segments

A new bisphenol monomer containing a pair of electron‐rich tetra‐arylmethane units was designed and synthesized. Based on this monomer, along with commercial 4,4′‐(hexafluoroisopropylidene)diphenol A and 4,4′‐difluorobenzophenone, a series of novel poly(arylene ether ketone)s containing octasulfonated segments of varying molar percentage (x) (6F‐SPAEK‐x) were successfully synthesized by polycondensation reactions, followed by sulfonation. Tough, flexible, and transparent membranes, exhibiting excellent thermal stabilities and mechanical properties were obtained by casting. 6F‐SPAEK‐x samples exhibited appropriate water uptake and swelling ratios at moderate ion exchange capacities (IECs) and excellent proton conductivities. The highest proton conductivity (215 mS cm⁻¹) is observed for hydrated 6F‐SPAEK‐15 (IEC = 1.68 meq g⁻¹) at 100 °C, which is more than 1.5 times that of Nafion 117. Furthermore, the 6F‐SPAEK‐10 membrane exhibited comparable proton conductivity (102 mS cm⁻¹) to that of Nafion 117 at 80 °C, with a relatively low IEC value (1.26 meq g⁻¹). Even under 30% relative humidity, the 6F‐SPAEK‐20 membrane (2.06 meq g⁻¹) showed adequate conductivity (2.1 mS cm⁻¹) compared with Nafion 117 (3.4 mS cm⁻¹). The excellent comprehensive properties of these membranes are attributed to well‐defined nanophase‐separated structures promoted by strong polarity differences between highly ionized and fluorinated hydrophobic segments. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 25–37     

Synthesis and characterization of poly(arylene ether ketone)s bearing pendant sulfonic acid groups for proton exchange membrane materials

A bisphenol monomer (2,5‐dimethoxy)phenylhydroquinone was prepared and further polymerized to obtain poly(arylene ether ketone) copolymers containing methoxy groups. After demethylation and sulfobutylation, a series of novel poly(arylene ether ketone)s bearing pendant sulfonic acid group (SPAEKs) with different sulfonation content were obtained. The chemical structures of all the copolymers were analyzed by ¹H NMR and ¹³C NMR spectra. Flexible and tough membranes with reasonably good mechanical properties were prepared. The resulting side‐chain‐type SPAEK membranes showed good dimensional stability, and their water uptake and swelling ratio were lower than those of conventional main‐chain‐type SPAEK membranes with similar ion exchange capacity. Proton conductivities of these side‐chain‐type sulfonated copolymers were higher than 0.01 S/cm and increased gradually with increasing temperature. Their methanol permeability values were in the range of 1.97 × 10^?7–5.81 × 10^?7 cm²/s, which were much lower than that of Nafion 117. A combination of suitable proton conductivities, low water uptake, low swelling ratio, and high methanol resistance for these side‐chain‐type SPAEK films indicated that they may be good candidate material for proton exchange membrane in fuel cell applications. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

A facile synthesis of cellulose acetate reinforced graphene oxide nanosheets as proton exchange membranes for fuel cell applications

In this work, for the first time, a simple casting process is used to create an efficient and highly stable cellulose acetate (CA) based membrane with dispersive graphene oxide nanosheets (GO). The successful preparation of GO and its integration into the polymer matrix was verified by structural and morphological characterization using FTIR, TEM, SEM, and XRD. Furthermore, the impact of GO nanosheets and their content on the composite membranes' physicochemical properties is investigated. The water uptake increased up to 24% as the concentration of GO increased, while the ion exchange capacity increased threefold compared to the blank CA membrane. Additionally, increasing GO loading also enhanced the proton conductivity and the tensile strength of the developed membranes. The homogeneous CA/GO nanocomposite membranes with GO filler amounts ranging from 0.3 to 0.8 wt% were found to have excellent proton conductivity varying from 9.2 to 15.5 mS/cm compared to 6.94 mS/cm for Nafion 212. Further, as systematically studied and compared in membrane performance, the overall power density of the membrane electrode assembly (MEA) with GO content was increased up to 519 mW/cm² compared to 401 mW/cm² for Nafion 212 with significantly lower cost. The encouraging outcomes of this study pave the way for a simple, environmentally friendly, and cost-effective approach for developing nanocomposite membranes for application in PEMFCs.     

Highly phosphonated poly(N‐phenylacrylamide) for proton exchange membranes

A novel highly phosphonated poly(N‐phenylacrylamide) ( PDPAA ) with an ion‐exchange capacity (IEC) of 6.72 mequiv/g was synthesized by the radical polymerization of N‐[2,4‐bis(diethoxyphosphinoyl)phenyl]acrylamide ( DEPAA ), followed by the hydrolysis with trimethylsilyl bromide. Then, the crosslinked PDPAA membrane was successfully prepared by the electrophilic substitution reaction between the aromatic rings of PDPAA and the carbocation formed from hexamethoxymethylmelamine (CYMEL) as a crosslinker in the presence of methanesulfonic acid. The crosslinked PDPAA membrane had high oxidative stability against Fenton's reagent at room temperature. The proton conductivity of the crosslinked PDPAA membrane was 8.8 × 10^?2 S/cm at 95% relative humidity (RH) and 80 °C, which was comparable to Nafion 112. Under low RH, the crosslinked PDPAA membrane showed the proton conductivity of 1.9 × 10^?3 and 4.7 × 10^?5 S/cm at 50 and 30% RH, respectively. The proton conductivity of the crosslinked PDPAA membrane lied in the highest class among the reported phosphonated polymers, and, consequently, the very high local concentration of the acids of PDPAA (IEC = 6.72 mequiv/g) achieved high and effective proton conduction under high RH. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Synthesis of ionic polybenzimidazoles with broad ion exchange capacity range for anion exchange membrane fuel cell application

In this study, new anion exchange membranes (AEM) based on crosslinked polybenzimidazole (m-PBI) with quaternary ammonium groups, crosslinkable allyl groups, and hydrophobic ethyl groups as side chains are synthesized and characterized. The AEMs are crosslinked by thermal thiol-ene reaction using a dithiol crosslinker. The ion exchange capacity (IEC) values and crosslinking density were controlled by the number of quaternary ammonium groups and allyl groups, respectively. The introduction of ethyl groups improved the solubility of ionic PBIs even at very low IEC values by eliminating the hydrogen bonding interaction of imidazole rings. This method allows ionic PBIs with broad IEC values, from 0.75 to 2.55 mmol/g, to be prepared. The broad IEC values were achieved by independently controlling the numbers of quaternary ammonium groups, allyl groups, and hydrophobic ethyl groups during preparation. The crosslinked ionic PBIs revealed hydroxide conductivity from 16 to 86 mS/cm at 80°C. The wet membranes also showed excellent mechanical strength with tensile strength of 12.2 to 20.1 MPa and Young's Modulus of 0.67 to 1.45 GPa. The hydroxide conductivity of a crosslinked membrane (0.40Q0.60Et1.00Pr, IEC = 0.95 mmol/g) decreased only 7.9% after the membranes was immersed in a 1.0 M sodium hydroxide solution at 80°C for 720 h. A single fuel cell based on this membrane showed a maximum peak power density of 136 mW/cm² with a current density of 377 mA /cm² at 60°C.     

Multiblock poly(Phenylene ether nitrile)s with pendant sulfoalkoxyl side chain for H2/air fuel cells at low humidity condition

A series of multiblock poly(phenylene ether nitrile)s with pendant sulfoalkoxyl side chains have been developed as proton exchange membranes for fuel cells. The membranes were obtained by a solution casting method and exhibited good thermal stability, flexibility, and mechanical strength. The membranes displayed well‐developed microphase separation, which largely contributed to their excellent ion conduction ability. One of the new membranes with a low ion exchange capacity of 1.57 mequiv g^?1 showed higher proton conductivity than Nafion 212 over the entire RH range (30–95%). The maximum power output generated in a single cell test reached up to 0.754, 0.640, and 0.414 W cm^?2 at 70 °C under 80%, 50%, and 30% RH conditions, respectively. The current density of the membrane obtained at 0.6 V (I _0.6) was as high as 640 mA cm^?2, which was much higher than that of Nafion 212 (375 mA cm^?2 at 30% RH), suggesting its superiority for a more rapid system start‐up. Furthermore, the in situ durability test at 50% RH was performed at a constant current loading, and the membrane did not show any significant voltage reduction over the 400 h testing period. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 1940–1948     

Mesoporous hollow silica spheres as micro-water-tanks in proton exchange membranes

In order to decrease the swelling of Nafion^® and reduce the dependency of proton conductivity on high relative humidity (RH), mesoporous hollow silica spheres were synthesized and dispersed in Nafion matrix as micro-water-tanks in the proton exchange membranes (PEM). The morphologies of MHSi and Nafion/MHSi composite membranes are characterized by SEM and TEM. The effects of MHSi on water uptake, swelling, dehydration rate and proton conductivity of the composite membranes were investigated. The results show that, with a suitable portion of MHSi in the membrane, composite PEMs with enhanced water uptake, reduced swelling and improved proton conductivity are obtained.     

Highly sulfonated multiblock copoly(ether sulfone)s for fuel cell membranes

Highly sulfonated multiblock copoly(ether sulfone)s applicable to proton electrolyte fuel cells (PEFCs) were synthesized by the coupling reaction of corresponding hydroxyl‐ terminated oligomers in the presence of highly reactive decafluorobiphenyl (DFB) as a chain extender, followed by postsulfonation with concentrated sulfuric acid. Their molecular weights were reasonably high as determined by viscosity measurement (η_inh = 0.72–1.58 dL/g). It was also confirmed that postsulfonation selectively took place in hydrophilic segments to yield highly sulfonated multiblock copolymers (IEC = 1.90–2.75 mequiv/g). The resulting polymers gave transparent, flexible, and tough membranes by solution casting. The 4b membrane, as a representative sample, demonstrated good mechanical strength in the dry state regardless of high IEC value (2.75 mequiv/g). The 4a–c membranes with higher IEC values (IEC = 2.75–2.79 mequiv/g) maintained high water uptake (13.7–17.7 wt %) at 50% RH and it was still high (7.4–8.5 wt %) at 30% RH. Proton conductivity of all membranes at 80 °C and 95% RH was higher than that of Nafion 117. Furthermore, the 4a membrane showed high proton conductivity, comparable with Nafion 117 in the range of 50–95% RH, and maintained high proton conductivity (2.3 × 10^?3 S/cm) even at 30% RH. Finally, the surface morphology of the membrane was investigated by tapping mode atomic force microscopy, which showed well‐connected hydrophilic domains that could work as proton transportation channel. This phase separation and the high water uptake behavior probably contributed to high and effective proton conduction in a wide range of relative humidity. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2757–2764, 2010     

Sulfonated polybenzimidazoles: Proton conduction and acid–base crosslinking

A series of soluble, benzimidazole‐based polymers containing sulfonic acid groups (SuPBI) has been synthesized. SuPBI membranes resist extensive swelling in water but are poor proton conductors. When blended with high ion exchange capacity (IEC) sulfonated poly(ether ether ketone) (SPEEK), a polymer that has high proton conductivity but poor mechanical integrity, ionic crosslinks form reducing the extent of swelling. The effect of sulfonation of PBI on crosslinking in these blends was gauged through comparison with nonsulfonated analogs. Sulfonic acid groups present in SuPBI compensate for acid groups involved in crosslinking, thereby increasing IEC and proton conductivity of the membrane. When water uptake and proton conductivity were compared to the IEC of blends containing either sulfonated or nonsulfonated PBI, no noticeable distinction between PBI types could be made. Comparisons were also made between these blends and pure SPEEK membranes of similar IEC. Blend membranes exhibit slightly lower maximum proton conductivity than pure SPEEK membranes (60 vs. 75 mS cm^?1) but had significantly enhanced dimensional stability upon immersion in water, especially at elevated temperature (80 °C). Elevated temperature measurements in humid environments show increased proton conductivity of the SuPBI membranes when compared with SPEEK‐only membranes of similar IEC (c.f. 55 for the blend vs. 42 mS cm^?1 for SPEEK at 80 °C, 90% relative humidity). © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3640–3650, 2010     

Chemically modified proton‐conducting membranes based on sulfonated polyimides: Improved water stability and fuel‐cell performance

A series of branched/crosslinked sulfonated polyimide (B/C‐SPI) membranes were prepared and evaluated as proton‐conducting ionomers based on the new concept of in situ crosslinking from sulfonated polyimide (SPI) oligomers and triamine monomers. Chemical branching and crosslinking in SPI oligomers with 1,3,5‐tris(4‐aminophenoxy)benzene as a crosslinker gave the polymer membranes very good water stability and mechanical properties under an accelerated aging treatment in water at 130 °C, despite their high ion‐exchange capacity (2.2–2.6 mequiv g^?1). The resulting polymer electrolytes displayed high proton conductivities of 0.2–0.3 S cm^?1 at 120 °C in water and reasonably high conductivities of 0.02–0.03 S cm^?1 at 50% relative humidity. In a single H₂/O₂ fuel‐cell system at 90 °C, they exhibited high fuel‐cell performances comparable to those of Nafion 112. The B/C‐SPI membranes also displayed good performances in a direct methanol fuel cell with methanol concentrations as high as 50 wt % that were superior to those of Nafion 112. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3751–3762, 2006     

Proton conducting membranes based on poly(vinyl chloride) graft copolymer electrolytes

The direct preparation of proton conducting poly(vinyl chloride) (PVC) graft copolymer electrolyte membranes using atom transfer radical polymerization (ATRP) is demonstrated. Here, direct initiation of the secondary chlorines of PVC facilitates grafting of a sulfonated monomer. A series of proton conducting graft copolymer electrolyte membranes, i.e. poly(vinyl chloride)‐g‐poly(styrene sulfonic acid) (PVC‐g‐PSSA) were prepared by ATRP using direct initiation of the secondary chlorines of PVC. The successful syntheses of graft copolymers were confirmed by ¹H‐NMR and FT‐IR spectroscopy. The images of transmission electron microscopy (TEM) presented the well‐defined microphase‐separated structure of the graft copolymer electrolyte membranes. All the properties of ion exchange capacity (IEC), water uptake, and proton conductivity for the membranes continuously increased with increasing PSSA contents. The characterization of the membranes by thermal gravimetric analysis (TGA) also demonstrated their high thermal stability up to 200°C. The membranes were further crosslinked using UV irradiation after converting chlorine atoms to azide groups, as revealed by FT‐IR spectroscopy. After crosslinking, water uptake significantly decreased from 207% to 84% and the tensile strength increased from 45.2 to 71.5 MPa with a marginal change of proton conductivity from 0.093 to 0.083 S cm^?1, which indicates that the crosslinked PVC‐g‐PSSA membranes are promising candidates for proton conducting materials for fuel cell applications. Copyright © 2008 John Wiley & Sons, Ltd.     

Sulfonated and crosslinked polyphosphazene-based proton-exchange membranes

Proton-exchange membranes, for possible use in H₂/O₂ and direct methanol fuel cells have been fabricated from poly[bis(3-methylphenoxy)phosphazene] by first sulfonating the base polymer with SO₃ and then solution-casting thin films. The ion-exchange capacity of the membrane was 1.4 mmol/g. Polymer crosslinking was carried out by dissolving benzophenone photoinitiator in the membrane casting solution and then exposing the resulting films after solvent evaporation to UV light. The crosslinked membranes look particularly promising for possible proton exchange membrane (PEM) fuel cell applications. A sulfonated and crosslinked polyphosphazene membrane swelled less than Nafion 117 in both water and methanol. Proton conductivities in crosslinked and non-crosslinked 200 μm thick water-equilibrated polyphosphazene films at temperatures between 25°C and 65°C were essentially the same and only 30% lower than those for Nafion 117. Additionally, water and methanol diffusivities in the crosslinked polyphosphazene membrane were very low (≤1.2×10⁻⁷ cm²/s). Sulfonated/crosslinked polyphosphazene films showed no signs of mechanical failure (softening) up to 173°C and a pressure of 800 kPa and did not degrade chemically when soaked in a hot hydrogen peroxide/ferrous ion solution.     

Novel sulphonated poly (vinyl chloride)/poly (2-acrylamido-2-methylpropane sulphonic acid) blends-based polyelectrolyte membranes for direct methanol fuel cells

Proton-conducting and methanol barrier properties of the proton exchange membrane (PEM), as well as the high cost of direct methanol fuel cell (DMFC) components, are the key determinants of the performance and commercialization of DMFCs. Therefore, this study aimed to develop cost- and performance-effective membranes based on sulphonated poly (vinyl chloride) (SPVC)/poly (2-acrylamido-2-methyl-1-propane sulphonic acid) (PAMPS) blends. Such membranes have been simply prepared by blending SPVC and PAMPS solutions, followed by solvent evaporation via casting. Interaction of SPVC with PAMPS was confirmed by different characterization techniques such as Fourier Transform Infra-red (FTIR) and Raman scattering spectroscopy in which the two characteristic absorption bands of sulfonic groups appeared at 1093 and 1219 cm⁻¹ additionally, strong peaks at around 1656 cm⁻¹ attributed to vibration of amide groups of PAMPS portion in the polymer blend. Furthermore, the interaction of SPVC with PAMPS improves the thermal properties along with ion exchange capacity in turn decreasing the methanol permeability through the membrane in comparison with the SPVC membrane. The IEC of PVC and Nafion 117 membranes were 1.25, 0.91 meq/g; respectively. And the maximum water uptake of PVC and Nafion 117 membranes were 75 and 65.44%; respectively. Methanol permeability value of 7.7 × 10⁻⁷ cm²/s which was noticeably lower than the corresponding value recorded for Nafion® (3.39 × 10⁻⁶ cm²/s). Therefore, these fabricated membranes can be considered a low-cost efficient candidate for use in DMFC, especially for its capability to resolve the methanol cross-over issue.     

Inorganic–organic hybrid polymers with pendent sulfonated cyclic phosphazene side groups as potential proton conductive materials for direct methanol fuel cells

A synthetic method is described to produce a proton conductive polymer membrane with a polynorbornane backbone and inorganic–organic cyclic phosphazene pendent groups that bear sulfonic acid units. This hybrid polymer combines the inherent hydrophobicity and flexibility of the organic polymer with the tuning advantages of the cyclic phosphazene to produce a membrane with high proton conductivity and low methanol crossover at room temperature. The ion exchange capacity (IEC), the water swelling behavior of the polymer, and the effect of gamma radiation crosslinking were studied, together with the proton conductivity and methanol permeability of these materials. A typical membrane had an IEC of 0.329 mmol g⁻¹ and had water swelling of 50 wt%. The maximum proton conductivity of 1.13 × 10⁻⁴ S cm⁻¹ at room temperature is less than values reported for some commercially available materials such as Nafion. However the average methanol permeability was around 10⁻⁹ cm s⁻¹, which is one hundred times smaller than the value for Nafion. Thus, the new polymers are candidates for low-temperature direct methanol fuel cell membranes.     

Enhancing proton conductivity of proton exchange membrane with SPES nanofibers containing porous organic cage

Effective proton conducting sites and establishing proton channels are two critical factors in developing high‐performance proton exchange membranes. This study first establishes a strategy in designing effective proton conducting channels for Nafion by using solution blowing of sulfonated polyethersulfone (SPES) nanofibers containing CC3, which is an emerging porous organic cage that possesses the advantages of dissolvable organic solvents and high proton conduction from its interconnected three‐dimensional pore structure. Our strategy results in SPES nanofiber networks with CC3 uniformly involved in and composite membranes with Nafion‐filled interfiber voids. Benefiting from such structural features, the composite membrane exhibits high proton conductivity (0.315 S cm^?1 at 80°C and 100% RH), low methanol permeability (0.69 × 10^?7 cm² S^?1), excellent water absorption, thermal and dimensional stability, and single‐cell performance. This study provides not only a valuable reference for the application of CC3 but also a new idea for establishment of proton transfer channels.     

Alternative proton-conducting electrolytes and their electrochemical performances

This study was focused on the performances of membrane electrode assemblies (MEAs) consisting of the proton–conducting 90PVA/3PWA/4GPTMS/1P₂O₅/2Gl and 80PVA/10PWA/6GPTMS/2P₂O₅/2Gl hybrid membranes as electrolytes together with a Pt/C electrode for proton exchange membrane fuel cells. The MEAs were fabricated and tested as a function of temperature and humidity, and yielded a current density value of about 350?mA?cm^?2 at 60?°C and 100% relative humidity (RH) for the membrane electrolyte 80PVA/10PWA/6GPTMS/2P₂O₅/2Gl. These values were compared with Nafion? membranes, and the single-cell performances based on proton-conducting organic/inorganic hybrid electrolytes were discussed. The test conditions employed were equivalent for each MEA that had an active area of 5?cm². These hybrid membranes showed a high proton conductivity in the range of 10^?3–10^?2 S cm^?1 at low temperatures, i.e., 60, 80, and 90?°C, and 50%, 75%, and 100% RH.     

Sulfonated poly(ether sulfone)s with binaphthyl units as proton exchange membranes for fuel cell application

Sulfonated poly(ether sulfone)s containing binaphthyl units (BNSHs) were successfully prepared for fuel cell application. BNSHs, which have very simple structures, were easily synthesized by postsulfonation of poly(1,1′‐dinaphthyl ether phenyl sulfone)s and gave tough, flexible, and transparent membranes by solvent casting. The BNSH membranes showed low water uptake compared to a typical sulfonated poly(ether ether sulfone) (BPSH‐40) membrane with a similar ion exchange capacity (IEC) value and water insolubility, even with a high IEC values of 3.19 mequiv/g because of their rigid and bulky structures. The BNSH‐100 membrane (IEC = 3.19 mequiv/g) exhibited excellent proton conductivity, which was comparable to or even higher than that of Nafion 117, over a range of 30–95% relative humidity (RH). The excellent proton conductivity, especially under low RH conditions, suggests that the BNSH‐100 membrane has excellent proton paths because of its high IEC value, and water insolubility due to the high hydrophobicity of the binaphthyl structure. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5827–5834, 2009     

Phosphoric acid‐doped imidazolium ionomers with enhanced stability for anhydrous proton‐exchange membrane applications

Phosphoric acid‐doped crosslinked proton‐conducting membranes with high anhydrous proton conductivity, and good chemical stability in phosphoric acid were synthesized and characterized. The synthetic procedure of the acid‐doped composite membranes mainly involves the in situ crosslinking of polymerizable monomer oils (styrene and acrylonitrile) and vinylimidazole, and followed by the sulfonation of pendant imidazole groups with butanesultone, and further doped with phosphoric acid. The resultant phosphoric acid‐doped composite electrolyte membranes are flexible and show high thermal stability and high‐proton conductivity up to the order of 10^?2 S cm^?1 at 160 °C under anhydrous conditions. The phosphoric acid uptake, swelling degree, and proton conductivity of the composite membranes increase with the vinylimidazole content. The resultant composite membranes also show good oxidative stability in Fenton's reagent (at 70 °C), and quite good chemical stability in phosphoric acid (at 160 °C). The properties of the prepared electrolyte membranes indicate their promising prospects in anhydrous proton‐exchange membrane applications. © 2013 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013 , 51, 1311–1317     

Novel proton-conductive nanochannel membranes with modified SiO2 nanospheres for direct methanol fuel cells

A novel approach is proposed to prepare a proton-conductive nanochannel membrane based on polyvinylidene difluoride (PVDF) porous membrane with modified SiO₂ nanospheres. The hydrophilic PVDF porous membrane with a 450-nm inner pore size was chosen as the supporting structure. Pristine SiO₂ with a uniform particle size of 95–110 nm was synthesized and functionalized with –NH₂ and –COOH, respectively. Through-plane channels of porous membrane and arranged functional nanoparticles in pores could contribute to constituting efficient proton transfer channels. The characteristics such as morphology, thermal stability, water uptake, dimensional swelling, proton conductivity and methanol permeability as proton exchange membranes, of the SiO₂ nanospheres, and the composite membrane were investigated. The formation of ionic channels in membrane enhanced the water uptakes and proton conduction abilities of the composite membranes. PVDF/Nafion/SiO₂–NH₂ exhibited superior proton conductivities (0.21 S cm^?1) over other samples due to several proton sites and the acid–base pairs formed between –NH₂ and –SO₃H. Furthermore, all the composite membranes exhibited improved methanol resistance compared with Nafion. Therefore, such a design based on porous membrane provided feasibility for high-performance proton exchange membrane in fuel cell applications.     

Proton conducting grafted/crosslinked membranes prepared from poly(vinylidene fluoride‐co‐chlorotrifluoroethylene) copolymer

Poly(vinylidene fluoride‐co‐chlorotrifluoroethylene) (P(VDF‐co‐CTFE)) backbone was grafted with crosslinkable chains of poly(hydroxyl ethyl acrylate) (PHEA) and proton conducting chains of poly(styrene sulfonic acid) (PSSA) to produce amphiphilic P(VDF‐co‐CTFE)‐g‐P(HEA‐co‐SSA) graft copolymer via atom transfer radical polymerization (ATRP). Successful synthesis and microphase‐separated structure of the copolymer were confirmed by ¹H NMR, FT‐IR spectroscopy, and TEM analysis. Furthermore, this graft copolymer was thermally crosslinked with sulfosuccinic acid (SA) to produce grafted/crosslinked membranes. Ion exchange capacity (IEC) increased continuously with increasing SA contents but the water uptake increased up to 6 wt% of SA concentration, above which it decreased monotonically. The membrane also exhibited a maximum proton conductivity of 0.062 S/cm at 6 wt% of SA concentration, resulting from competitive effect between the increase of ionic groups and the degree of crosslinking. XRD patterns also revealed that the crystalline structures of P(VDF‐co‐CTFE) disrupted upon graft polymerization and crosslinking. These membranes exhibited good thermal stability at least up to 250°C, as revealed by TGA. Copyright © 2009 John Wiley & Sons, Ltd.