Durability of a novel sulfonated polyimide membrane in polymer electrolyte fuel cell operation

A novel sulfonated polyimide membrane containing triazole groups (SPI-8) was subjected to long-term fuel cell operation. Excellent durability of the SPI-8 membrane was confirmed by single cell operation for 5000 h at 80 °C. Open circuit voltage and hydrogen crossover through the membrane showed only minor changes during cell operation, indicating a lack of catastrophic damage for the SPI-8 membrane. It was found by post-test analyses of the membrane that the ion exchange capacity (IEC) decreased only slightly, but the molecular weight decreased to 1/10, resulting in a loss of mechanical strength. It was concluded that the major degradation mode of the sulfonated polyimide membrane involves the ring-opening of the imide linkages via hydrolysis, while a certain degree of side chain degradation occurs as a result of oxidative attack by radical species.     

SPES‐SiO2 hybrid proton exchange membranes from in situ sol–gel process of negatively charged alkoxysilane

One type of negatively charged alkoxysilane, that is, sulfonated 3‐(mercaptopropyl)trimethoxysilane (SMPTS), has been developed from 3‐(mercaptopropyl)trimethoxysilane (MPTS) and hydrogen peroxide. SMPTS is used to modify sulfonated poly(ether sulfone) (SPES) through in situ sol–gel process. The membranes with proper SMPTS dosage show enhanced ion exchange capacity (IEC), hydrophilicity, mechanical strength, chemical stability, and proton conductivity, which prove that SMPTS is an effective modifier for preparing proton‐exchange hybrid membranes. With MPTS of 5–20%, the hybrid membranes exhibit IEC 1.34–1.50 mmol g^?1, thermal stability 264–316°C, and proton conductivity 0.0015–0.0102 S cm^?1 and thus recommended for potential application in fuel cells. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Transport in sulfonated poly(phenylene)s: Proton conductivity, permeability, and the state of water

The transport properties of a series of sulfonated poly(phenylene)s were found to strongly correlate to the ion exchange capacity of the polymer. Sulfonated poly(phenylene) membranes have shown promise as proton exchange membranes for fuel cells. In general, these materials have minimal methanol and glucose crossover while maintaining high proton conductivity, which is necessary for efficient operation of fuel cells powered by liquid fuels. Proton conductivity in addition to methanol and glucose permeability were compared to Nafion as a function of ion exchange capacity. It was found that the transport in Nafion membranes was much higher than that in the sulfonated poly(phenylene)s for a given ion exchange capacity. Water content and its absorbed state within membranes were elucidated by differential scanning calorimetry in order to provide insight as to how the transport properties varied between the materials studied. The domain morphology of these ionomers was imaged with transmission electron microscopy in order to contrast the morphological differences between Nafion and the sulfonated poly(phenylene) series.     

Multiblock sulfonated-fluorinated poly(arylene ether)s for a proton exchange membrane fuel cell

New proton exchange membranes were prepared and evaluated as polymer electrolytes for a proton exchange membrane fuel cell (PEMFC). Sulfonated-fluorinated poly(arylene ether) multiblocks (MBs) were synthesized by nucleophilic aromatic substitution of highly activated fluorine terminated telechelics made from decafluorobiphenyl with 4,4′-(hexafluoroisopropylidene)diphenol and hydroxyl-terminated telechelics made from 4,4′-biphenol and 3,3′-disulfonated-4,4′-dichlorodiphenylsulfone. Membranes with various sulfonation levels were successfully cast from N-methyl-2-pyrrolidinone. An increase sulfonated block size in the copolymer resulted in enhanced membrane ion exchange capacity and proton conductivity. The morphological structure of MB copolymers was investigated by tapping mode atomic force microscopy (TM-AFM) and compared with those of Nafion^® and sulfonated poly(arylene ether) random copolymers. AFM images of MBs revealed a very well defined phase separation, which may explain their higher proton conductivities compared to the random copolymers. The results are of particular interest for hydrogen/air fuel cells where conductivity at high temperature and low relative humidity is a critical issue.     

Highly sulfonated poly(phenylene sulfones): optimization of the polymerization conditions

The preparation of highly sulfonated poly(phenylene sulfone) (ion exchange capacity = 4.45 meq g⁻¹) by polycondensation of sulfonated difluorodiphenyl sulfone with metal sulfide and subsequent oxidation with hydrogen peroxide is optimized. The monomer/metal sulfide ratio, polymerization time and temperature, and type of metal sulfide have been varied. For the best conditions high molecular weights of up to 300 kg mol⁻¹ are obtained reproducibly. This high molecular weight polyelectrolyte is meant to be used as main constituent of heterogeneous membrane structures such as interpenetrating networks, polymer blends, or simple physical mixtures with other polymers, e.g., for application in PEM fuel cells.     

Preparation of poly(ethylene terephthalate)‐based proton‐exchange membranes through the ultraviolet‐induced graft copolymerization of allyl methacrylate for applications in fuel cells

The ultraviolet‐induced graft copolymerization of allyl methacrylate into poly(ethylene terephthalate) films and the subsequent sulfonation of the grafted film were performed to prepare a polymer electrolyte membrane (PEM). The sulfonation reaction occurred at the grafted chain under mild conditions; that is, the grafted film was easily transformed into a PEM. The mechanical, chemical, and thermal properties of the prepared PEM (i.e., the ion‐exchange capacity, water uptake, tensile strengths at different water uptakes and temperatures, stability in hydrogen peroxide solutions, and proton conductivity) were measured with titrimetric and gravimetric analyses; most were found to be better than those of Nafion. The maximum ion‐exchange capacity and proton conductivity of the PEM were observed to be 0.072 mmol/g and 0.0458 S/cm, respectively. Because this PEM is inexpensive to prepare with available raw materials and has the properties required for fuel cells, it could be an attractive and suitable device for use in fuel‐cell technology. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Sulfonated poly(arylene ether sulfone)/Laponite-SO3H composite membrane for direct methanol fuel cell

Polymer nanocomposite membranes based on sulfonated poly(arylene ether sulfonate) (SPAES) containing a flake filler (Laponite) with varying degrees of sulfonation, were prepared and characterized for application in direct methanol fuel cells (DMFCs). Unlike most other clays, Laponite crystals are very small in size with a very low aspect ratio (diameter to thickness ratio) of 25–30. They improve the mechanical, thermal properties and decreased the fuel permeability. However, polymer composite membranes containing non-proton conducting inorganic particles tend to show low proton conductivity, as compared with pristine polymer membranes. To resolve this problem, prior to the preparation of the composite membranes, Laponite-Na+(NLa) was sulfonated with various amounts of organo silanes (3-Mercaptopropyl trimethoxysilane (SH-silane)) via an ion exchange method. Functionalized Laponite with the organic silane compound showed higher ion exchange capacity and ion conductivity, respectively. In order to minimize the loss of proton conductivity while reducing the methanol permeability, various amounts (0.5–2.0 wt%) of the organically sulfonated Laponite (SLa) were introduced into the SPAES matrices. The performances of hybrid membranes for DMFCs in terms of mechanical properties, behavior of water in membranes, proton conductivity and methanol permeability were investigated.     

Effect of crosslinking on the physicochemical properties of proton conducting PVDF-g-PSSA membranes

Poly(vinylidene fluoride) (PVDF) membranes, radiation-grafted with styrene and sulfonated, were studied as a candidate material for polymer electrolyte fuel cell (PEFC). In particular the effect of the use of crosslinkers in the polymer structure was investigated using bis(vinyl phenyl)ethane (BVPE) and divinylbenzene (DVB) as reagents. Water uptake in the H+ form, proton conductivity and ion exchange capacity of the PVDF-g-PSSA membranes, as well as transport properties of oxygen and hydrogen were determined at room temperature. Crosslinking with DVB resulted in a more pronounced decrease in the properties; the use of BVPE had no significant influence. Even on the permeation of oxygen and hydrogen the BVPE had little effect: the diffusion coefficient and solubility remained at the same level as for the non-crosslinked membranes. Increasing the membrane thickness was found to be at least as effective in reducing the oxygen permeation rate as using crosslinkers.     

A new synthesis approach for proton exchange membranes based on ultra-high-molecular-weight polyethylene

A new approach for gas-phase modification of ultra-high-molecular-weight polyethylene (UHMWPE) film for synthesis of proton exchange membranes (PEMs) has been successfully realized. First, the membrane precursors have been prepared by soaking the films in a monomers/AIBN solution followed by their modification with polystyrene (PS) in styrene vapor at 110°C. The developed method is characterized by high efficiency, simplicity, and ecological purity. The modified UHMWPE films containing up to 60 wt% of PS have been obtained. Then, PEMs were prepared by sulfonation of these precursors. According to energy-dispersive X-ray spectroscopy of the sulfonated samples, almost uniform distribution of PS through the film thickness was observed. The membranes with an ion exchange capacity up to 2.7 mmol/g and proton conductivity up to 60 mS/cm (water, 25°C) were obtained. Comparative tests of the obtained UHMWPE-sulfonated PS and commercial Nafion-115 membranes in a hydrogen–air fuel cell have been carried out. It has been shown that the cell with the synthesized membranes exhibits better performance than that with Nafion-115.     

Proton conducting blend membranes: physical,morphological and electronic properties

Blend membranes of sulfonated poly(ether ether ketone) (SPEEK) and sulfonated polyetherimide (SPEI) have been prepared and investigated as a potential polymer electrolyte membrane (PEM) for direct methanol fuel cell (DMFC). Polymers were dissolved in N-methyl-2-pyrrolidone (NMP) in different mixing ratios and membranes were casted using a semi-automatic casting machine on a pre-cleaned glass plate. The influence of SPEI percentage on ion exchange capacity (IEC), water uptake, methanol permeability and proton exchange capacity have been investigated. Blend membranes showed slightly better IEC, water uptake and methanol crossover properties as compare to pure SPEEK; but proton conductivity was slightly lower than that of pure SPEEK membrane. Membrane morphology was investigated by FESEM, TGA and AFM. Overall, a homogeneous surface was observed for most of the blend membranes, with minor phase separation at higher SPEI contents samples. AFM image of the membrane surface shows nanoscale surface roughness.     

六元环型磺化聚酰亚胺类质子交换膜

磺化聚酰亚胺是一类很有希望在燃料电池中获得应用的质子交换膜材料。本文对近年来六元环型磺化聚酰亚胺的制备、磺化聚酰亚胺质子交换膜的各项性能做了一定的归纳与分析。重点介绍了耐水性、耐久性、离子交换容量、质子电导率四个方面的测试方法及影响因素,指出目前存在的问题并预测了今后重点研究的方向。     

Synthesis of new sulfonated copolyimides in organic and ionic liquid media for fuel cell application

New sulfonated copolyimides containing ether, carbonyl, and bulky naphthyl group in backbone were synthesized in two reaction media: organic solvent and ionic liquid media. For this purpose a new sulfonated diamine (BANBPDS) and an unsulfonated diamine (BANBP) was prepared through reactions of 4,4′‐dichlorobenzophenone‐3,3′‐disulfonic acid, and also 4,4′‐dichlorobenzophenone with 5‐amino‐1‐sodium naphthoxide, respectively. Three series of sulfonated copolyimide with different sulfonation contents (40–80%) were prepared by reaction of the sulfonated diamine (BANBPDS) in companion with three unsulfonated diamines including BANBP, 4,4′‐oxydianiline (ODA), and 1,8‐diamino‐3,6‐dioxaoctane (DADO) with 1,4,5,8‐naphthalene tetracarboxylic dianhydride (NTDA). Two media were selected for preparation of copolyimides. Copolyimides synthesized in ionic liquid had higher inherent viscosity and higher molecular weight in comparison with similar copolyimides that were synthesized via common organic solvent method. Incorporation of flexible groups in polyimide structures increased solubility and processability of the copolyimides. After characterization of polymers with common methods, their water uptake, water stability, ion exchange capacity (IEC), thermal behavior and stability, crystallinity, and morphology were studied. The polymers showed suitable properties including high thermal stability and ion exchange capacity, which were the basic requirements for application as fuel cell membranes. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Dendronized Polymer Architectures for Fuel Cell Membranes

Multi‐step synthetic pathways to low‐ion exchange capacity (IEC) polysulfone (PSU) with sulfonic acid functionalized aliphatic dendrons and sulfonated comb‐type PSU structures are developed and investigated in a comparative study as non‐fluorinated proton exchange membrane (PEM) candidates. In each case the side chains are synthesized and introduced in their sulfonated form onto an azide‐functionalized PSU via click chemistry. Three degrees of substitution of each architecture were prepared in order to evaluate the dependence on number of sulfonated side chains. Solution cast membranes were evaluated as PEMs for use in fuel cells by proton conductivity measurements, and in the case of dendronized architectures: thermal stability. The proposed synthetic strategy facilitates exploration of a non‐fluorous system with various flexible side chains where IEC is tunable by the degree of substitution.     

Sulfonated hydrocarbon membranes for medium-temperature and low-humidity proton exchange membrane fuel cells (PEMFCs)

This review summarizes efforts in developing sulfonated hydrocarbon proton exchange membranes (PEMs) with excellent long-term electrochemical fuel cell performance in medium-temperature and/or low-humidity proton exchange membrane fuel cell (PEMFC) applications. Sulfonated hydrocarbon PEMs are alternatives to commercially available perfluorosulfonic acid ionomers (PFSA, e.g., Nafion^®) that inevitably lose proton conductivity when exposed to harsh operating conditions. Over the past few decades, a variety of approaches have been suggested to optimize polymer architectures and define post-synthesis treatments in order to further improve the properties of a specific material. Strategies for copolymer syntheses are summarized and future challenges are identified. Research pertaining to the sulfonation process, which is carried out in the initial hydrocarbon PEM fabrication stages, is first introduced. Recent synthetic approaches are then presented, focusing on the polymer design to enhance PEM performance, such as high proton conductivity even with a low ion exchange capacity (IEC) and high dimensional stability. Polymer chemistry methods for the physico-chemical tuning of sulfonated PEMs are also discussed within the framework of maximizing the electrochemical performance of copolymers in membrane-electrode assemblies (MEAs). The discussion will cover crosslinking, surface fluorination, thermal annealing, and organic–inorganic nanocomposite approaches.     

Effects of crosslinking time and amount of sulfophthalic acid on properties of the sulfonated poly(vinyl alcohol) membrane

A proton‐exchange membrane for a direct methanol fuel cell was prepared by modifying the chemical structure of poly(vinyl alcohol) (PVA) via a sulfonation. The sulfonation was carried out by using sulfophthalic acid (sPTA) as a sulfonating agent. The sulfonated PVA membranes, with a variety of degrees of substitutions, were obtained by varying the crosslinking time and the amount of sulfonating agents. The chemical structure and thermal stability of the sulfonated PVA were characterized by using FTIR and thermogravimetric analysis techniques, respectively. The ion‐exchange capacity (IEC) and water uptake of the sulfonated membranes was evaluated by titration and gravimetry techniques, respectively. It was found that the IEC of the membrane increased with the amount of sPTA. Water uptakes of the membranes could either decrease or remain unchanged with the crosslinking time, depending on the amount of the sulfonating agent used. Methanol permeability values of the membranes treated with 10% sPTA were relatively low, comparing with that of the Nafion 115 membrane. Proton conductivity values of the sulfonated PVA membranes ranged between 0.024 and 0.035 S/cm and they did not remarkably change with the crosslinking time. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1931–1936, 2006     

Effect of hydrogen peroxide bleaching onto sulfonated jute fiber

Bleaching of raw and sulfonated jute fiber with hydrogen peroxide were carried out in an aqueous medium. To obtain the optimum condition for bleaching, the effects of hydrogen peroxide concentration, temperature, time, pH, and fiber–liquor ration were studied. Bleaching affected the whiteness and tenacity, and the optimum whiteness index (76) and tenacity (13.7 g/tex) for the bleached sulfonated jute fiber were obtained with 2.1% hydrogen peroxide at pH 11, temperature 95°C, treatment time 110 min, and fiber–liquor ratio 1 : 7. The photo‐oxidative degradation of bleached sulfonated jute fiber was characterized by UV light exposure and compared with that of bleached raw jute fiber. It has been observed that the photo‐oxidative degradation as well as loss in tenacity and yellowness of the bleached sulfonated jute fiber was 63 and 40% lower than that of bleached raw jute fiber. Bleached sulfonated jute fiber had excellent impact on color fastness with reactive dyes. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3603–3607, 2006     

Structure-property-performance relationships of sulfonated poly(arylene ether sulfone)s as a polymer electrolyte for fuel cell applications

This article focuses on structure-property-performance relationships of directly copolymerized sulfonated polysulfone polymer electrolyte membranes. The chemical structure of the bisphenol-based disulfonated polysulfones was systematically alternated by introducing fluorine moieties or other polar functional groups such as benzonitrile or phenyl phosphine oxide in the copolymer backbone. Ac impedance measurements of the polymer electrolyte membranes indicated that fluorine incorporation increased proton conductivity, while polar functional group incorporation decreased conductivity. Likewise, other properties such as water uptake and ion exchange capacity are impacted by the incorporation of fluorine moiety or polar groups. These properties are critically tied with H₂/air and direct methanol fuel cell performance. We have rationalized fuel cell performance of these selected copolymers in light of structure-property relationships, which gives useful insight for the development and application of next generation polymer electrolytes.     

Sulfonated aromatic hydrocarbon polymers as proton exchange membranes for fuel cells

This article reviews recent studies on proton exchange membrane (PEM) materials for polymer electrolyte fuel cells. In particular, it focuses on the development of novel sulfonated aromatic hydrocarbon polymers for PEMs as alternatives to conventional perfluorinated polymers. It is necessary to improve proton conductivity especially under low-humidity conditions at high operating temperatures to breakthrough the current aromatic PEM system. Capable strategies involve the formation of well-connected proton channels by microphase separation between hydrophilic and hydrophobic domains and the increase of the ion exchange capacity of PEMs while keeping water resistance. Herein, we introduce novel molecular designs of sulfonated aromatic hydrocarbon polymers and their performance as PEMs.     

Proton conductivity and methanol permeability of sulfonated poly(vinyl alcohol) membranes modified by using sulfoacetic acid and poly(acrylic acid)

Sulfonated poly(vinyl alcohol) (PVA) for use as a proton conductive membrane in a direct methanol fuel cell (DMFC) was prepared by reacting the PVA with sulfoacetic acid and poly(acrylic acid). The effects of the amount of sulfoacetic acid and poly(acrylic acid) on proton conductivity, methanol permeability, water uptake, and ion exchange capacity (IEC) of the sulfonated PVA membranes were investigated by using impedance analysis, gas chromatography, gravimetric analysis, and titration techniques, respectively. The water uptake of the membranes decreased with the amount of the sulfoacetic acid and the amount of poly(acrylic acid) used. The proton conductivity and the IEC values of the membranes initially increased and then decreased with the amount of the sulfoacetic acid. The methanol permeability of the sulfonated PVA membranes decreased continuously with the amount of the sulfoacetic acid. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Novel sulfonated poly(ether ether ketone ketone) derived from bisphenol S

A series of sulfonated poly(ether ether ketone ketone)s derived from bisphenol S were prepared by nucleophilic polycondensation. They showed high thermal resistance and good solubility. Most of the polymers were easily cast into tough membranes. The swelling of the membranes (6.02–16.02%) was lower than that of Nafion membranes, and the ion‐exchange capacity of the membranes (0.67–1.44) was higher than that of Nafion membranes. The proton conductivity of the membranes was 0.022–0.125 s/cm. They could be used as proton‐exchange membranes in fuel cells. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1569–1574, 2004