A novel sulfonated diamine, 4,4′‐bis(4‐amino‐3‐trifluoromethylphenoxy) biphenyl 3,3′‐disulfonic acid (F‐BAPBDS), was successfully synthesized by nucleophilic aromatic substitution of 4,4′‐dihydroxybiphenyl with 2‐chloro‐5‐nitrobenzotrifluoride, followed by reduction and sulfonation. A series of sulfonated polyimides of high molecular weight (SPI‐x, x represents the molar percentage of the sulfonated monomer) were prepared by copolymerization of 1,4,5,8‐naphathlenetetracarboxylic dianhydride (NTDA) with F‐BAPBDS and nonsulfonated diamine. Flexible and tough membranes of high mechanical strength were obtained by solution casting and the electrolyte properties of the polymers were intensively investigated. The copolymer membranes exhibited excellent oxidative stability due to the introducing of the CF3 groups. The SPI membranes displayed desirable proton conductivity (0.52×10−1–0.97×10−1 S·cm−1) and low methanol permeability (less than 2.8×10−7 cm2·s−1). The highest proton conductivity (1.89×10−1 S·cm−1) was obtained for the SPI‐90 membrane at 80°C, with an IEC of 2.12 mequiv/g. This value is higher than that of Nafion 117 (1.7×10−1 S·cm−1). Furthermore, the hydrolytic stability of the obtained SPIs is better than the BDSA and ODADS based SPIs due to the hydrophobic CF3 groups which protect the imide ring from being attacked by water molecules, in spite of its strong electron‐withdrawing behaviors. 相似文献
Two multiblock copoly(arylene ether sulfone)s with similar block lengths and ion exchange capacities (IECs) were prepared by a coupling reaction between a non‐sulfonated precursor block and a highly sulfonated precursor block containing either fully disulfonated diarylsulfone or fully tetrasulfonated tetraaryldisulfone segments. The latter two precursor blocks were sulfonated via lithiation‐sulfination reactions whereby the sulfonic acid groups were exclusively placed in ortho positions to the many sulfone bridges, giving these blocks IECs of 4.1 and 4.6 meq·g−1, respectively. Copolymer membranes with IECs of 1.4 meq·g−1 displayed well‐connected hydrophilic nanophase domains and had decomposition temperatures at, or above, 300 °C under air. The copolymer with the tetrasulfonated tetraaryldisulfone segments showed a proton conductivity of 0.13 S·cm−1 at 80 °C under fully humidified conditions, and surpassed that of a perfluorosulfonic acid membrane (NRE212) by a factor of 5 at –20 °C over time.
With a view towards direct methanol fuel cell applications, novel sulfonated poly(phenylene sulfide sulfone nitrile) (sPPSSfN) has been prepared and subsequently crosslinked by a Friedel‐Craft reaction using 4,4′‐oxybis(benzoic acid) as a crosslinker to achieve lower water swelling and lower methanol permeability. The dimensional change of SPPSSfN40 is 43.7% in 90 °C liquid water but that of the crosslinked membrane, XsPPSSfN40, is 23.3% while maintaining proton conductivity at 0.22 S · cm−1. These results show that the Friedel‐Craft crosslinking of the novel sPPSSfN membrane effectively reduces water uptake and the degree of swelling while improving the dimensional stability and maintaining high proton conductivity.
Nafion/TiO2 composite membranes for different loadings of TiO2 were prepared by casting method for the possible application in direct ethanol fuel cell (DEFC). The properties of the composite membranes were investigated by scanning electron microscopy (SEM), x-ray diffraction (XRD), thermogravimetric analyser (TGA), ion exchange capacity, water and alcohol uptake, swelling ratio, proton conductivity, and ethanol crossover. The observed characteristics of the membranes were evaluated for DEFC and compared with the direct methanol fuel cell (DMFC) membrane. The analysis reveales a significant influence on the TiO2 surface characteristics, water and alcohol uptake, and swelling of the membrane. The TiO2 composite membranes exhibited a sharp decrease in methanol and ethanol crossover for 5% TiO2 and the proton conductivity was heighest for 1% TiO2 loading. The best compromise between proton conductivity and crossover has been found out with the help of the characteristic factor ϕ. The optimum loading of 5% TiO2 composite membrane has shown the maximum characteristic factor. 相似文献
Summary: Branched/crosslinked sulfonated polyimide membranes incorporating superior mechanical properties, high proton conductivity, and excellent fuel cell performance were successfully developed. The resulting polymer electrolytes displayed conductivity values of about 0.2 S · cm−1 at 120 °C and 100% relative humidity. In a single H2/O2 fuel cell system at 90 °C, they exhibited reasonably high fuel cell performances comparable to that of Nafion 112.
The structure of the branched/crosslinked sulfonated polyimide membranes studied here. 相似文献
This study describes a new strategy to improve the performance of PEMFCs by the addition of S/CNF. The presence of 2.08 vol.‐% S/CNF increased the proton conductivity of a S/EPDM by one order of magnitude, which made it comparable to that of Nafion® 117, and without creating an electronic path. Furthermore, the filled membranes showed improved thermal stability and mechanical properties.
Summary: SPTES polymers have been successfully synthesized by direct polymerization using tetramethylene sulfone as the solvent. The chemical structures of the SPTES polymers are confirmed by FT‐IR and NMR spectroscopy. The thermal stability is characterized by TGA, and the results show that the sulfonated groups on the polymer backbone are stable up to 300 °C. The measured proton conductivity reaches values above 300 mS · cm−1 at 65 °C and 85% relative humidity. Tough, ductile, free‐standing membranes have been fabricated by solution casting from N,N‐dimethylacetamide, which indicates that the SPTES polymers have excellent membrane‐forming capability and mechanical property. The mono‐functional monomers are introduced into the polymerization to end‐cap the SPTES polymers. The end‐capping groups are effective in improving water resistance, oxidative stability, and retaining the proton conductivity.
AbstractPoly(vinyl alcohol) (PVA) is a biodegradable, water-soluble membrane that has low methanol permeation and reactive chemical functionalities. Modification of these features makes PVA an attractive proton exchange membrane (PEM) alternative to NafionTM. However, the pristine PVA membrane is a poorer proton conductor than the NafionTM membrane due to the absence of negatively charged ions. Hence, modification of PVA matrixes whilst complying with the requirements of projected applications has been examined extensively. Generally, three modification methods of PVA membranes have been highlighted in previous reports, and these are (1) grafting copolymerization, (2) physical and chemical crosslinking, and (3) blending of polymers. The use of each modification method in different applications is reviewed in this study. Although the three modification methods can improve PVA membranes, the mixed method of modification provides another attractive approach. This review covers recent studies on PVA-based PEM in different fuel cell applications, including (1) proton-exchange membrane fuel cells and (2) direct-methanol fuel cells. The challenges involved in the use of PVA-based PEM are also presented, and several approaches are proposed for further study. 相似文献
