The effect of crosslinked networks with poly(ethylene glycol) on sulfonated polyimide for polymer electrolyte membrane fuel cell

To investigate the effect of crosslinking by a hydrophilic group on a sulfonated polyimide electrolyte membrane, sulfonated polyimide end‐capped with maleic anhydride was synthesized using 1,4,5,8‐naphthalenetetracarboxylic dianhydride, 4,4′‐diaminobiphenyl, 2,2′‐disulfonic acid, 2‐bis [4‐(4‐aminophenoxy)phenyl] hexafluropropane and maleic anhydride. The sulfonated polyimides end‐capped with maleic anhydride were self‐crosslinked or crosslinked with poly(ethylene glycol) diacrylate. A series of the crosslinked sulfonated polyimides having various ratios of sulfonated polyimide and poly(ethylene glycol) diacrylate were prepared and compared with uncrosslinked and self‐crosslinked sulfonated polyimides. The synthesized sulfonated polyimide films were characterized for FTIR spectrum, thermal stability, ion exchange capacity, water uptake, hydrolytic stability, morphological structure, and proton conductivity. The formation of sulfonated polyimide was confirmed in FTIR spectrum. Thermal stability was good for all the sulfonated polyimides that exhibited a three‐step degradation pattern. Ion exchange capacity was the same for both the uncrosslinked and the self‐crosslinked sulfonated polyimides (1.30 mEq/g). When the crosslinked sulfonated polyimides with poly(ethylene glycol) were compared, the ion exchange capacity was decreased as 1.27 > 1.25 > 1.23 mEq/g and water uptake was increased as 23.8 < 24.0 < 24.3% with the increase in poly(ethylene glycol) diacrylate content. All the crosslinked sulfonated polyimides with poly(ethylene glycol) diacrylate were stable for over 200 h at 80 °C in deionized water. Morphological structure and mean intermolecular distance were obtained by WAXD. Proton conductivities were measured at 30, 50, 70, and 90 °C. The proton conductivity of the crosslinked sulfonated polyimides with poly(ethylene glycol) diacrylate increased with the increase in poly(ethylene glycol) diacrylate content despite the fact that the ion exchange capacity was decreased. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1455–1464, 2005     

Sulfonated Poly(ether ether ketone) and Poly(ethylene glycol) Diacrylate Based Semi-Interpenetrating Network Membranes for Fuel Cells

Polymer electrolyte membranes are prepared from novel semi-interpenetrating polymer network material where the sulfonated poly (ether ether ketone) (SPEEK) is the linear polymer and the poly (ethylene glycol) diacrylate (PEGDA) is the cross-linking constituent. The semi-IPN is prepared by in situ polymerization of PEGDA in the presence of sulfonated poly (ether ether ketone). SPEEK is prepared by direct sulfonation of commercial PEEK (Gatone? 1100) by reported procedures. SPEEK with degree of sulfonation 63% (calculated from FT-NMR) is selected as the base membrane and different semi-IPN membranes were prepared by varying the PEGDA and SPEEK ratio. The degree of sulfonation of SPEEK and the formation of semi-IPN were confirmed by spectroscopy studies. The various semi-IPN membranes were characterized for ion-exchange capacity, water uptake, hydrolytic stability, proton conductivity and thermal stability for evaluating the suitability of these membranes for fuel cells. The proton conductivity of the membranes decreased with increasing PEGDA content. The Semi-IPN membranes exhibited conductivities (30°C) from 0.018 S/cm to 0.006 S/cm. These interpenetrating network membranes showed higher hydrolytic stability than the pure SPEEK membrane. This study shows that semi-IPN membranes based on PEGDA and SPEEK can be viable candidates for electrolyte membranes.     

Characterizations and stability of polyimide-phosphotungstic acid composite electrolyte membranes for fuel cell

Organic-inorganic composite membranes from partially aliphatic sulfonated polyimides and heteropolyacids (HPAs) were synthesized. A series of composite membranes with varying amounts of heteropolyacid were prepared by altering the weight ratio of polyimide and HPA. The partially aliphatic sulfonated polyimides are synthesized from 1,4,5,8-naphthalenetetracarboxylic dianhydride, 4,4′-diaminobiphenyl 2,2′-disulfonic acid as the sulfonated diamine, and decamethylenediamine as the aliphatic diamine. The incorporation of HPA is confirmed by FT-IR analyses. When appropriately embedded in a hydrophilic polymer matrix, the hydrated HPAs are expected to endow the composite membrane with their high proton conductivity, while retaining the desirable mechanical properties of the polymer film. These composite membranes were evaluated for thermal stability, ion exchange capacity, water uptake and proton conductivity. Also the extraction of HPA from the polyimide membranes and their stability in water were determined. Though water uptake and IEC decreased with increase in HPA content, the proton conductivity of the composite membranes increased with increase in HPA weight content. This study shows that partially aliphatic sulfonated polyimide composite membranes with HPA can be a viable substitute for Nafion^® for fuel cells which show good conductivity comparable to Nafion^®117 at temperatures nearing 100 °C, keeping in mind that polyimides have good thermal stability and low cost.     

Physicochemical characterization of ion-exchange membranes in water-methanol mixtures

A complete physicochemical characterization of two ion-exchange membranes—CM2 and Nafion^®117—used in electrodialysis and in direct methanol fuel cells (DMFC) has been carried out. For each membrane, in different methanol-water mixtures—0%, 20%, 40%, 60%, 80% and 100%—and at different temperatures (25.0; 40.0 et 55.0 °C), we have measured the variations of the geometrical dimensions, the proton electrical conductivity, the swelling rate and the amount of methanol in the membrane. The FTIR analysis of Nafion^®117 was performed at different methanol contents of the external solution.The results show that the CM2 membrane presents the best geometrical stability, and the lowest conductivity at any methanol content. At high methanol contents, Nafion^®117 is 10 times more conductive than the CM2 membrane. It was found that the methanol is absorbed more by Nafion^®117, and its effect is more noticeable on the microstructure of this membrane, under standard conditions. The high methanol permeability of these membranes, particularly of the Nafion^®117, induces bad cell efficiencies and lifetimes.     

High efficiency direct methanol fuel cell based on poly(styrenesulfonic) acid (PSSA)-poly(vinylidene fluoride) (PVDF) composite membranes

semi-Interpenetrating polymer network (sIPN) composite membranes consisting of poly(styrenesuflonic) acid (PSSA) and poly(vinylidene fluoride) (PVDF) have been prepared and evaluated as proton exchange membrane electrolytes in direct methanol fuel cells (DMFCs). The membranes fabricated were evaluated in terms of their proton conductivity, methanol permeability, and their performance characteristics in direct methanol fuel cells (DMFCs). PSSA-PVDF membranes demonstrated decreased methanol crossover during operation of direct methanol fuel cells compared to state-of-art Nafion^®-H membranes, yielding improved efficiency. PSSA-PVDF membranes have been demonstrated to operate efficiently in 1 in. × 1 in. and 2 in. × 2 in. direct methanol fuel cells. Fuel cells operating with PSSA-PVDF membranes were observed to have dramatically lower crossover rates compared to Nafion^® 117 systems. Greater than 95% reduction in crossover was observed in some cases. These properties of PSSA-PVDF membranes resulted in improved fuel performance and fuel cell efficiencies for direct methanol fuel cells. It was also observed that the PSSA-PVDF membranes behave quite differently compared with Nafion^®-based systems in terms water management characteristics at the cathode. The best performance with the new membranes was observed with very low oxygen or air flow rates at the cathode which is in contrast to Nafion^®-based systems, which generally require higher flow rates due to excessive water accumulation at the cathode, resulting in flooding.     

Dimensionally stable Nafion–polyethylene composite membranes for direct methanol fuel cell applications

Nafion^® impregnated Solupor^®, microporous UHMWPE film, (N-PE), Nafion^®117 (N117) and a membrane prepared using a DE2020 Nafion^® dispersion (DE2020) were characterized with respect to their swelling degree (SD), methanol cross-over, proton conductivity and DMFC performance at various methanol concentrations in order to understand the effect of impregnation of an ion-conductive polymer membrane to the fuel cell performance.     

Semi-interpenetrating polymer networks toward sulfonated poly(ether ether ketone) membranes for high concentration direct methanol fuel cell

Semi-IPNs were constructed by forming the crosslinking networks via the reaction between BPPO and diamine cross-linkers to overcome the dimensional swelling and methanol-permeation issues of SPEEK.     

Synthesis of novel crosslinked sulfonated poly(ether sulfone)s using bisazide and their properties for fuel cell application

Novel crosslinked sulfonated poly(ether sulfone)s (PESs) were prepared by thermal irradiation of the allyl-terminated telechelic sulfone polymers using a bisazide. The sulfonated polymers in different comonomer compositions were fully characterized by ¹H NMR, and the crosslinked structure was also verified by FT-IR spectroscopic analyses. Having both the uniform distribution of the hydrophilic conductive sites and controlled hydrophobic nature by minimized crosslinking over the rigid rod poly(ether sulfone) backbone, the crosslinked polymer membrane (PES-60) offered excellent proton conductivity of 0.79 S cm⁻¹ at 100 °C together with hydrolytic and oxidative stability. In addition, only 17% of methanol permeability of the Nafion^® was observed for the crosslinked PES-60.     

Synthesis of fluoro-containing sulfonated poly(phthalazinone ether ketone ketone)s and their properties as PEM in PEMFC and DMFC

A series of sulfonated poly(ether ketone ketone)s (SPPFEKKs) containing both of phthalazinone and hexafluoroisopropylidene moieties were synthesized by direct nucleophilic polycondensation reaction from 4-(4-hydroxyphenyl)-1(2H)-phthalazinone (DHPZ), 4,4-hexafluoroisopropylidene-diphenol (BPAF), 1,4-bi(4-fluorobenzoyl) benzene (DFKK) and 1,4-bi(3-sodium sulfonate-4-fluorobenzoyl) benzene (SDFKK). The obtained SPPFEKKs had high molecular weight with inherent viscosity ranged from 1.29 to 1.53 dL/g and their chemical structure was characterized by FT-IR and ¹H NMR. The ionic membranes of SPPFEKKs showed high proton conductivity, for instance, SPPFEKK-120 (DS = 1.20) demonstrated 1.0 × 10⁻¹ S/cm proton conductivity at 95 °C, which was very close to that of Nafion^®117. All the SPPFEKK membranes exhibited methanol permeability lower than 2.76 × 10⁻⁷ cm²/s, which was much lower than that of Nafion^®117 (2.38 × 10⁻⁶ cm²/s). These copolymers also showed excellent thermal stability and good solubility in aprotic polar organic solvents. The ionic membranes of SPPFEKK demonstrated tensile strength varied from 57 to 69 MPa depending on their DS.     

磺化聚芳醚砜/磺化聚酰亚胺复合质子交换膜的制备与性能研究

利用溶液浇铸法制备了一系列双磺化型磺化聚芳醚砜/磺化聚酰亚胺(SPAES/SPI)复合质子交换膜.扫描电子显微镜(SEM)结果显示复合膜不存在明显的相分离,表明二者具有很好的相容性.由于SPI的引入,复合膜在甲醇中稳定性较纯SPAES具有大幅的提高,比Nafion112低得多的甲醇吸收率表明了这些复合膜具有比后者更低的甲醇透过率.复合膜显示了与单组分膜相类似的高温分解稳定性,磺酸基团的分解温度达到了290℃以上.复合膜显示出远高于纯SPAES膜的尺寸稳定性能,在130℃高温中200h处理后,所有的复合膜均保持了高的机械性能,而此时纯SPAES膜已经溶解于水中.而且由于两种磺化聚合物间的复合,复合膜维持了较高的IEC水平,显示了较高的质子导电率,在80%相对湿度时的质子导电率与Nafion112相近,而在水中的质子导电率均高于Nafion112.     

Zirconium meta-sulfonphenyl phosphonic acid-incorporated Nafion membranes for reduction of methanol permeability

Zirconium meta-sulfonphenyl phosphonic acid (Zr-msPPA)/Nafion^® composite membranes were prepared to reduce methanol permeability of the Nafion^® 117 membrane in direct methanol fuel cell (DMFC) applications. Zr-msPPA crystalline nano proton conductors were synthesized inside the membranes via the reaction of zirconium chloride octahydrate and meta-sulfonphenyl phosphonic acid that had been soaked prior. Synthesis of the Zr-msPPA in the membranes was identified from a series of chemical and physical structure characterizations using FTIR, NMR, EDS, and XRD spectroscopy. The thermal stability of the composite membranes was enhanced by addition of the Zr-msPPA, with considerable reduction in methanol permeability with increasing Zr-msPPA content, as the Zr-msPPA nano conductors acted as crystalline barriers to methanol permeation. The ion conductivity also decreased with increasing Zr-msPPA content, but its effect was not as strong as with methanol permeation given the innate, high conductivity of Zr-msPPA.     

Preparation and properties of Nafion/hollow silica spheres composite membranes

In present work, hollow silica spheres (HSS)/Nafion^® composite membranes were prepared by solution casting. The thermal properties, water retention, swelling behavior and proton conductivity of the composite membranes were explored. It was found that HSS dispersed well at micrometer scale in the obtained composite membranes by SEM and TEM observation. Thermal properties of composite membranes were improved than that of recast Nafion^® membrane. Compared with the recast Nafion^® membrane, the composite membranes showed higher water uptake and lower swelling degree at the temperature range from 40 to 100 °C. At the same HSS loading, the smaller the diameter of HSS in composite membranes, the more the water uptake, however, the swelling degree of composite membranes was increased. The proton conductivity of the composite membrane with 3–5 wt.% HSS (120 and 250 nm) increased distinctively at above 60 °C, reached the optimal value at 100 °C, and decreased slowly when the temperature exceeded 100 °C.     

Modification of proton conductive polymer membranes with phosphonated polysilsesquioxanes

New hybrid membranes for fuel cell applications based on sulfonated poly(ether ether ketone) (SPEEK) and phosphonated polysilsesquioxanes were synthesized. The impedance spectroscopy measurements show an increase of the proton conductivity for all studied composites, in comparison to plain SPEEK. For hybrid membranes containing 20 wt% of polysilsesquioxane with 80 mol% of phosphonated units the conductivities can reach values that are similar to Nafion 117^® at 100% RH. The best results of proton conductivity (142 mS/cm) were obtained for composites with 40 wt% of the same polysilsesquioxane at 120 °C also at 100% RH.     

Sulfonated poly(fluorenyl ether) membranes containing perfluorocyclobutane groups for fuel cell applications

This paper describes the preparation and electrochemical properties of new proton conducting polymer membranes, sulfonated poly(fluorenyl ether) membrane-containing perfluorocyclobutane (PFCB) moieties for fuel cell applications. The sulfonated polymers were prepared via thermal cyclodimerization of 9,9-bis(4-trifluorovinyloxyphenyl)fluorene and subsequent post-sulfonation using chlorosulfonic acid (CSA) as a sulfonating agent. The post-sulfonation reaction was carried out by changing the molar ratio of CSA/repeating unit of the polymer at room temperature for 5 h and the resulting sulfonated polymers showed different degrees of sulfonation (DS) and ion exchange capacities (IEC). With the increment of CSA content, the DS, IEC and water uptake of the sulfonated polymer membranes increased. Their proton conductivity was investigated as a function of temperature. The polymer membrane with an IEC value of 1.86 mmol/g showed a water content of 25% similar to Nafion-115's but showed higher proton conductivity than Nafion-115 over the temperature 25–80 °C. The polymer membrane with lower water uptake and higher IEC showed similar proton conductivity and methanol permeability to Nafion-115. These results confirmed that the sulfonated poly(fluorenyl ether)-containing PFCB groups could be a promising material for fuel cell membranes.     

Investigation of sulfonated poly(ether ether ketone sulfone)/heteropolyacid composite membranes for high temperature fuel cell applications

The sulfonated poly(ether ether ketone sulfone) (SPEEKS)/heteropolyacid (HPA) composite membranes with different HPA content in SPEEKS copolymers matrix with different degree of sulfonation (DS) were investigated for high temperature proton exchange membrane fuel cells. Composite membranes were characterized by Fourier transfer infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). FTIR band shifts suggested that the sulfonic acid groups on the copolymer backbone strongly interact with HPA particles. SEM pictures showed that the HPA particles were uniformly distributed throughout the SPEEKS membranes matrix and particle sizes decreased with the increment of copolymers' DS. The holes were not found in SPEEKS‐4/HPA30 (consisting of 70% SPEEKS copolymers with DS = 0.8 and 30% HPA) composite membrane after composite membranes were treated with boiling water for 24 h. Thermal stabilities of the composite membranes were better than those of pure sulfonated copolymers membranes. Although the composite membranes possessed lower water uptake, it exhibited higher proton conductivity for SPEEKS‐4/HPA30 especially at high temperature (above 100 °C). Its proton conductivity linearly increased from 0.068 S/cm at 25 °C to 0.095 S/cm at 120 °C, which was higher than 0.06 S/cm of Nafion 117. In contrast, proton conductivity of pure SPEEKS‐4 membrane only increased from 0.062 S/cm at 25 °C to 0.078 S/cm at 80 °C. At 120 °C, proton conductivity decreased to poor 0.073 S/cm. The result indicated that composite membranes exhibited high proton conductivity at high temperature. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1967–1978, 2006     

Energy material - the role of silicotungstic acid and fly ash in sulfonated poly (ether sulfone) composites for PEMFC applications

The composite polymer electrolyte membranes were prepared from sulfonated poly (ether sulfone) (SPES), silicotungstic acid (STA) and fly ash (FA). Post sulfonation process was adopted to synthesize SPES using sulphuric and chlorosulfonic acid. The prepared electrolyte membranes were examined by water uptake capacity, swelling ratio, ion-exchange ability, proton conductivity, thermal stability and electrochemical performance for evaluating the pertinence of these membranes in fuel cell applications. As such the pristine membrane restricts with the proton conductivity of 0.042?S cm^?1 at 30?°C and 0.060?S cm^?1 at 90?°C while the polymer composite membrane, SP-STA-FA-10 reveals the maximum conductivity of 0.054?S cm^?1 at 30?°C and 0.073?S cm^?1 at 90?°C. It also exhibits good thermal stability than that of the pure membrane. The membrane electrode assemblies (MEAs) have been successfully developed from SPES as well as SP-STA-FA-10 membranes and their electrochemical performance were studied the wide range of current density. Herein, the composite membranes derived from SPES, STA and FA can be viable candidates for fuel cell applications.     

Preliminary evaluation of sulfonated poly(ether ether ketone)/monoethanolamine/adipic acid composite membranes for direct methanol fuel cell applications

A series of sulfonated poly(ether ether ketone)/monoethanolamine/adipic acid (SPEEK/MEA/AA) composite membranes are prepared and investigated to assess their possibility as proton exchange membranes in direct methanol fuel cells (DMFCs). A preliminary evaluation shows that introducing MEA and AA into SPEEK matrix decreases the thermal stability of membrane. However, the degradation temperatures are still above 260 °C, satisfying the requirement for fuel cell operation. Compared with the pure SPEEK membrane, the composite membranes exhibit not only lower water uptake and swelling ratios but also better mechanical property and oxidative stability. Noticeably, the methanol diffusion coefficient of the composite membranes decrease significantly from 3.15 × 10^?6 to 0.76 × 10^?6 cm²/s with increasing MEA and AA content, accompanied by only a small sacrifice in proton conductivity. Although both the methanol diffusion coefficient and the proton conductivity of composite membranes are lower than those of pure SPEEK and Nafion® 117 membranes, their selectivity (conductivity/methanol diffusion coefficient) are higher. In addition, the composite membranes show excellent stability in aqueous methanol solution. The good thermal and chemical stability, low swelling ratio, excellent mechanical property, low methanol diffusion coefficient, and high selectivity make the use of these composite membranes in DMFCs quite attractive. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2871–2879, 2007     

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     

Proton exchange membrane using partially sulfonated polystyrene-b-poly(dimethylsiloxane) for direct methanol fuel cell

A diblock copolymer ionomer containing a rubbery poly(dimethylsiloxane) block has been developed as a proton exchange membrane for direct methanol fuel cell (DMFC). The partially sulfonated polystyrene-b-poly(dimethylsiloxane) (sPS-b-PDMS) membrane with 38% sulfonation degree exhibited 3 times lower methanol permeability and 2.6 times higher membrane selectivity (proton conductivity/methanol permeability) compared to Nafion^® 115 at 25 °C. Coexistence of microphase domains and ionic clusters was confirmed from the morphological studies by small-angle X-ray scattering and tapping-mode atomic force microscopy. Gas chromatographic analysis revealed that water/methanol selectivity of sPS-b-PDMS was 20 times higher than that of Nafion^® 115. Such a high water/methanol selectivity can be attributed to the existence of PDMS microdomains minimizing methanol permeation through hydrophilic ion channels. sPS-b-PDMS membranes were fabricated into membrane electrode assembly (MEA), and air-breathing DMFC test for these MEAs showed a better performance compared to the MEA composed of Nafion^® 115.     

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