Sulfonated Polyimide Research Articles

Synthesis and Properties of Sulfonated Polyimide/Polybenzimidazole Cross-Linked Membranes for Fuel Cell Applications

A series of cross-linked proton exchange membranes with the ion exchange capacities (IECs) of 0.70 - 1.52 meq/g have been prepared via the reaction of the anhydride-terminated sulfonated polyimide oligomers (SPI-3, SPI-5 and SPI-7, here the figure refers to the averaged block length) and the polybenzimidazole with pendant amino groups (H2N-PBI) in dimethylsulfoxide (DMSO) during the membrane cast process. The prepared cross-linked membranes showed high tensile strength (55 - 80 MPa) and good water stability (> 2 months in deionized water at 100 °C). Fenton’s test revealed that all the cross-linked membranes displayed significantly better radical oxidative stability than the corresponding pure SPIs. This is attributed to the presence of the highly oxidative-stable PBI component in the cross-linked membranes. The proton conductivities of the cross-linked membranes increased with increasing temperature and relative humidity. The cross-linked membrane prepared from the longest oligomer (SPI-7) displayed the highest proton conductivity which is comparable to that of Nafion 117.

Sulfonated polyimides containing pyridine groups as proton exchange membrane materials

A series of sulfonated polyimides (SPIs) containing pyridine groups were prepared by direct polycondensation from 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTDA), 4,4′-diaminodiphenyl ether-2,2′-disulfonic acid (ODADS) and 4-(4-methoxy)phenyl-2,6-bis(4-aminophenyl)pyridine (DAM). The resulting copolymers displayed good solubility in common organic solvents. Flexible, transparent, tough membranes were obtained via solution casting. All the films showed high thermal stability with desulfonation temperature over 300°C. They exhibited prominent mechanical properties with Young’s modulus around 2.0 GPa. High proton conductivity (0.23 S/cm at 100% RH) was also observed. More importantly, the new materials exhibited low water uptake (30 wt%–75 wt% at 80°C) and improved water stability, which were attributed to the acid-base interaction between sulfonic acid and pyridine functional groups.

Proton Exchange Membrane Based on Sulfonated Polyimide for Fuel Cells: State-of-the-Art and Recent Developments

Proton exchange membrane is one of the most important components for proton exchange membrane fuel cells (PEMFCs). The preparation of proton exchange membranes based on sulfonated polyimide (SPI) for PEMFCs in recent years was reviewed, and methods of improving the water stability and proton conductivity of such membranes were highlighted. It was suggested that preparation of novel SPI membranes or organic-inorganic composite SPI membranes should be a reasonable approach to strengthen their combination property.

Preparation and Properties of Sulfonated Polyimide Proton Conductive Membrane for Vanadium Redox Flow Battery

A series of sulfonated polyimides (SPIs) were synthesized by 1,4,5,8-naphthalene tetracarboxylic dianhydride (NTDA), 2,2′-benzidinedisulfonic acid (BDSA) and 4,4′- diaminodiphenyl ether (ODA) in m-cresol. The sulfonation degree of SPI was controlled through the ratio of sulfonated diamine to the non-sulfonated diamine, and the SPI membranes were prepared by a casting method. The chemical structures of SPI membranes were characterized by FT-IR. The properties of obtained SPI membranes were investigated, such as water uptake, ion exchange capacity, proton conductivity and permeability of vanadium ion. The proton conductivities of SPI membranes are ranged from 0.012 to 0.051 S/cm, and the permeabilities of vanadium ion are one or two orders of magnitude less than that of Nafion® 117 (1.80×10-6cm2/min ). Experimental results showed that SPI membranes are potential candidates for vanadium redox flow battery.

Polyimide ionomer containing superacid groups

A novel sulfonated polyimide (SPI) copolymer containing pendant perfluorosulfonic acid groups was synthesized and their properties were investigated. 2‐(2,4‐Diaminophenoxy)‐1,1,2,2‐tetrafluoroethanesulfonic acid (5) was synthesized from 2,4‐diaminophenol dihydrochloride via acetylation, perfluoroalkylation, and sulfonation. Polycondensation of 1,4,5,8‐naphthalenetetracarboxylic dianhydride, monomer 5, and 3,5‐bis(4‐aminophenyl)‐1H‐1,2,4‐triazole gave the title polyimide 6. The obtained polyimide copolymer 6 was soluble in polar organic solvents and its chemical structure and ion exchange capacity were confirmed by 1H and 19F NMR spectra. The copolymer 6 was thermally stable up to ca. 180°C and showed 6.6 × 10−4 S cm−1 of the proton conductivity at 80°C in water. Copyright © 2011 John Wiley & Sons, Ltd.

Preparation and properties of sulfonated poly(phenylene arylene)/sulfonated polyimide (SPA/SPI) blend membranes for polymer electrolyte membrane fuel cell applications

A novel series of sulfonated poly(phenylene arylene)s (SPAs) were successfully synthesized from 2,5-dichloro-3′-sulfobenzophenone (DCSB) and 2,2′-bis[4-(4-chlorobenzoyl)]phenoxyl perfluoropropane (BCPPF) by Ni(0)-catalyzed coupling polymerization, and subsequently used as the start materials to prepare blend membranes with sulfonated polyimide (SPI) for polymer electrolyte membrane fuel cell (PEMFC) applications. The miscible structure of the prepared blend membranes was confirmed by scanning electron microscopy (SEM). The properties required for a PEM such as ion exchange capacity, water uptake, solution uptake and dimensional change and/or in water or methanol solutions, proton conductivity and hydrolytic stability were investigated in details. The obtained blend SPA/SPI membranes showed rather high proton conductivities in both the plane and the thickness direction of the membrane. They exhibited slightly anisotropic proton conductivity in water with σ⊥/∥ values in the range of 0.85–0.90, irrespective of the introduction of SPI (σ⊥/∥=0.73). They also showed significantly enhanced stability in water and methanol solutions compared with the corresponding SPA membranes. All the results indicated that this type of blend membranes were quite promising candidates for PEMFC applications.

A Mesothermal Fuel Cell using Diethylmethylammonium Trifluoromethanesulfonate Absorbed Membrane with H3PO4 Addition and Various Amount of Electrolyte Loading in Catalyst Layer

In order to improve the fuel cell performance using a diethylmethylammonium trifluoromethanesulfate ([dema] [TfO]) absorbed sulfonated polyimide membrane, the effects of H3PO4 addition to the [dema] [TfO] and the loading amount of [dema] [TfO] in the gas diffusion electrode have been investigated. The ohmic resistance decreased with an increase in the [dema] [TfO] loading, which would correspond to the ohmic resistance between the electrode and the electrolyte membrane. The 5 mol% of H3PO4 addition enhanced the cell performance by accelerating the mass transfer, and the reaction polarization was a minimum at a 2.1 mg cm−2 the [dema] [TfO] loading.

Tuning transport properties by manipulating the phase segregation of tetramethyldisiloxane segments in modified polyimide electrolytes

A series of copolymer electrolytes containing 4,4′-oxydianiline (ODA)-based sulfonated polyimide and siloxane segments, in various ratios, are prepared and characterized for direct methanol fuel cell applications. The chemical Structure of the sulfonated copolymers is confirmed by FT-IR and NMR. The prepared composite membranes are found to be flexible and show good thermal stability as well as good proton conductivity. A maximum proton conductivity of 5.78 × 10 −2 S cm −1 (cf. Nafion117 = 8.31 × 10 −2 S cm −1) is obtained for the sulfonated polyimide blended with sulfonated polyimide with a grafted tetramethyldisiloxane segment (cf. SPI_DSX75 membrane) at 90 °C. The membranes showed low methanol crossover below 10 −7 cm 2 s −1 (cf. Nafion117 = 10 −6 cm 2 s −1). The transport properties of the membranes are found to be strongly influenced by water uptake and by the number and nature of the ionic clusters in the hydrophilic domains. When the number of siloxane segments is increased, the relationship between the methanol self-diffusion coefficient ( D M ) and water molecules per sulfonic acid group ( λ) indicate that the water molecules are interacting with channels inside the membrane. In addition, the segregated nanophase also affects the ion transport and sometimes enhances the corresponding ionic conductivity. TEM and SAXS analyses shows evidence for phase segregation in the membranes and reveal the influence of flexible siloxane segments in ionic clustering.

In situ sol-gel route to novel sulfonated polyimideSiO2 hybrid proton-exchange membranes for direct methanol fuel cells

Polyimides (PIs) as high-performance organic matrices are used in the preparation of PI composites because of their excellent mechanical, thermal and dielectric properties. The sol–gel method is a promising technique for preparing these PI composites due to the mild reaction conditions and the process being controllable. Although sulfonated polyimide (SPI) proton-exchange membranes have attracted much attention recently, studies on preparing SPI-based hybrid proton-exchange membranes for fuel cells have been rare. A series of SPISiO2 hybrid proton-exchange membranes were prepared from amino-terminated SPI pre-polymers, 3-glycidoxypropyltrimethoxysilane (KH-560) and tetraethylorthosilicate through a co-hydrolysis and condensation process using an in situ sol–gel method. The reactive silane KH-560 was used to react with amino-terminated SPI to form silane-capped SPI in order to improve the compatibility between the polymer matrix and the inorganic SiO2 phase. The microstructure and mechanical, thermal and proton conduction properties were studied in detail. The hybrid membranes were highly uniform without phase separation up to 30 wt% SiO2. The storage modulus and tensile strength of the hybrid membranes increased with increasing SiO2 content. The introduction of SiO2 improved the methanol resistance while retaining good proton conductivity. The hybrid membrane with 30 wt% SiO2 exhibited a proton conductivity of 10.57 mS cm−1 at 80 °C and methanol permeability of 2.3 × 10−6 cm2 s−1 possibly because the crosslinking structure and SiO2 phases formed in the hybrids could retain water and were helpful to proton transport. Copyright © 2010 Society of Chemical Industry

Sulfonated polyimides with flexible aliphatic side chains for polymer electrolyte fuel cells

A series of sulfonated polyimides (SPIs) were synthesized from a new side group sulfonated diamine, 2,2′-bis(4-sulfobutoxy) benzidine monomer (2,2′-BSBB), 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTDA), and common nonsulfonated diamine monomers by polycondensation reaction. Membranes were prepared by casting their m-cresol solutions. The SPI membranes displayed proton conductivity σ values of 0.2–0.4 S cm −1 at 140 °C in liquid water and showed stronger relative humidity (RH) dependence of proton conductivity compared to that of Nafion 112. Most of the SPI membranes were both tough and flexible and thermally stable up to 230–250 °C. XRD spectra suggested the presence of crystalline structure in the membranes. TEM analysis indicated clear microphase separation structure between hydrophobic main chain and hydrophilic side chain. The fully humidified SPI membranes exhibited obvious anisotropic dimensional changes with much larger expansion in thickness than in plane. The long term proton conductivity stability (ca. 500 h) was confirmed at 140 °C. The methanol permeabilities ( P M ) of the SPI membranes were in the range of 4.0 × 10 −7–1.2 × 10 −6 cm 2/s with a 50 wt% methanol in feed at 30 °C, which were one order of magnitude smaller than that of Nafion 112. As a result, the membranes displayed much larger selectivity towards both high proton conductance and low methanol permeation, compared to Nafion 112, suggesting high potential application for direct methanol fuel cells (DMFCs).

Novel nanocomposite membranes based on sulfonated mesoporous silica nanoparticles modified sulfonated polyimides for direct methanol fuel cells

Novel nanocomposite proton exchange membranes were prepared by using sulfonated mesoporous silica nanoparticles (SMSNs) as inorganic fillers through direct blending with sulfonated polyimides (SPIs). The microstructure and properties of the resulting hybrid membranes were studied. The SMSNs with a diameter of 50–300 nm exhibited the ordered mesopores of about 2.3 nm. The introduction of sulfonated mesoporous silica improved the thermal stability, water uptake and methanol permeability of the resulting nanocomposite membranes as compared with SPI. The hybrid membrane with 3 wt% SMSNs showed the highest water-uptake value of 54.2% and lowest methanol permeability value of 5.23 × 10 −6 cm 2 s −1. When the content of SMSNs was higher than 3 wt%, both the values decreased slightly because of the aggregation of SMSNs. All of the membranes showed the excellent proton conductivity as compared with Nafion 117. When 7 wt% SMSNs were incorporated into the SPI, the membrane sample presented the highest proton conductivity at different testing temperatures, indicating that the addition of SMSNs can also improve the proton conductivity of composite membranes.

Nonhumidified Intermediate Temperature Fuel Cells Using Protic Ionic Liquids

In this paper, the characterization of a protic ionic liquid, diethylmethylammonium trifluoromethanesulfonate ([dema][TfO]), as a proton conductor for a fuel cell and the fabrication of a membrane-type fuel cell system using [dema][TfO] under nonhumidified conditions at intermediate temperatures are described in detail. In terms of physicochemical and electrochemical properties, [dema][TfO] exhibits high activity for fuel cell electrode reactions (i.e., the hydrogen oxidation reaction (HOR) and oxygen reduction reaction (ORR)) at a Pt electrode, and the open circuit voltage (OCV) of a liquid fuel cell is 1.03 V at 150 degrees C, as has reported in ref 27. However, diethylmethylammonium bis(trifluoromethane sulfonyl)amide ([dema][NTf(2)]) has relatively low HOR and ORR activity, and thus, the OCV is ca. 0.7 V, although [dema][NTf(2)] and [dema][TfO] have an identical cation ([dema]) and similar thermal and bulk-transport properties. Proton conduction occurs mainly via the vehicle mechanism in [dema][TfO] and the proton transference number (t(+)) is 0.5-0.6. This relatively low t(+) appears to be more disadvantageous for a proton conductor than for other electrolytes such as hydrated sulfonated polymer electrolyte membranes (t(+) = 1.0). However, fast proton-exchange reactions occur between ammonium cations and amines in a model compound. This indicates that the proton-exchange mechanism contributes to the fuel cell system under operation, where deprotonated amines are continuously generated by the cathodic reaction, and that polarization of the cell is avoided. Six-membered sulfonated polyimides in the diethylmethylammonium form exhibit excellent compatibility with [dema][TfO]. The composite membranes can be obtained up to a [dema][TfO] content of 80 wt % and exhibit good thermal stability, high ionic conductivity, and mechanical strength and gas permeation comparable to those of hydrated Nafion. H(2)/O(2) fuel cells prepared using the composite membranes can successfully operate at temperatures from 30 to 140 degrees C under nonhumidified conditions, and a current density of 250 mA cm(-2) is achieved at 120 degrees C. The protic ionic liquid and its composite membrane are a possible candidate for an electrolyte of a H(2)/O(2) fuel cell that operates under nonhumidified conditions.

Synthesis and characterization of sulfonated polyimides bearing sulfonated aromatic pendant group for DMFC applications

A novel side-chain-type sulfonated aromatic diamine, 5-[1,1-bis(4-aminophenyl)-2,2,2- trifluoroethyl]-2-(4-sulfophenoxy)benzenesulfonic acid (BABSA) was synthesized and characterized. Two series of sulfonated polymides (SPI-N and SPI-B) were prepared from 1,4,5,8-naphthalene tetracarboxylic dianhydride (NTDA) or 4,4′-binaphthyl-1,1′,8,8′-tetracarboxylic dianhydride (BNTDA), sulfonated diamine BABSA and various non-sulfonated aromatic diamines. The resulting sulfonated polyimide (SPI) membranes exhibited good dimensional stability with isotropic swelling of 7–22% and high thermal stability with desulfonation temperature of 283–330 °C. These membranes also displayed excellent oxidation stability and good water stability. The SPI membranes exhibited better permselectivity than Nafion 115 membrane due to their much lower methanol permeability. The ratios of proton conductivity to methanol permeability (Ф) for the SPI membranes were almost two to three times of that for Nafion 115. The SPI-N membranes exhibited excellent conducting performance with the proton conductivity higher than Nafion 115 as the temperature over 40 °C, which attributed to their good hydrophobic/hydrophilic microphase separation structure.

Proton conductive polyimide ionomer membranes: Effect of NH, OH, and COOH groups

AbstractA new series of sulfonated polyimide (SPI) copolymers containing NH, OH, or COOH groups were synthesized by the polycondensation of 1,4,5,8‐naphthalnetetracarboxylic dianhydride, 3,3′‐bis(sulfopropoxy)‐4,4′‐diaminobiphenyl, and 3‐(4‐aminophenyl)‐5‐(3‐aminophenyl)‐1H‐1,2,4‐triazole (SPI‐8‐m), 3,5‐bis(4‐aminophenyl)‐1H‐1,2,4‐triazole (SPI‐8‐p), 3,6‐diaminocarbazole (SPI‐9), 3,5‐diamino‐1H‐1,2,4‐triazole (SPI‐10), bis(3‐aminopropyl)‐amine (SPI‐11), 2,6‐diaminopurine (SPI‐12), 2,4‐diamino‐6‐hydroxyprymidine (SPI‐13), or 3,5‐bis(4‐aminophenoxy)benzoic acid (SPI‐14). The obtained SPIs were soluble in polar organic solvents and gave tough and flexible membranes by solution casting. The SPI membranes having NH and COOH groups showed high thermal (decomposition temperature ≈200 °C) and mechanical (maximum stress >22 MPa) stability. Introducing NH groups, especially triazole and carbazole groups, was effective in improving proton conductive properties of SPI membranes at low humidity. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2846–2854, 2010

Survey of sulfonated polyimide membrane as a good candidate for nafion substitution in fuel cell

Studies in fuel cell membranes show that modification of polyimides by introduction of aliphatic linkages in the structure of sulfonated copolyimides, synthesis of branched/crosslinked sulfonated polyimides, and semi and fully interpenetrating polymer networks of sulfonated polyimides restrain suitable potential for Nafion substitution.

Syntheses of sulfonated star-hyperbranched polyimides and their proton exchange membrane properties

We synthesized novel sulfonated star-hyperbranched polyimides composed of a hydrophobic hyperbranched polymer for polymer stability and a hydrophilic sulfonated polyimide as the proton-transport site in the core–shell structure. The proton conductivities of the star-hyperbranched polyimide membranes were measured as functions of the relative humidity and temperature using electrochemical impedance spectroscopy. Although the water uptake and IEC value for the sulfonated star-hyperbranched polyimide membranes were almost constant, the proton conductivity of the membrane strongly depended on the molecular weight of the hydrophilic sulfonated polyimide as the shell. Especially, the conductivity of the high molecular weight star-hyperbranched polyimide membranes was significantly superior to that determined in Nafion ® at all temperatures and was 0.51 S cm −1 at 80 °C and 98% RH, which may suggest that a good proton-transport pathway in the core–shell structure is formed. Consequently, this material proved to be promising as a proton exchange membrane and may have potential applications for use in fuel cells.

Sulfonated polyimides bearing benzimidazole groups for direct methanol fuel cell applications

Sulfonated polyimides (SPIs) bearing benzimidazole groups in the main chains were synthesized from 1,4,5,8-naphthalenetetracarboxiylic dianhydride, 4,4′-bis(4-aminophenoxy)biphenyl-3,3′-disulfonic acid and 2-( p- or m-aminophenyl)-5-aminobenzimidazole in m-cresol. The resulting polymer solutions were not precipitated to gain the solid polymers but directly cast into films because the precipitated SPIs became insoluble in common organic solvents. The strong interaction between sulfonic acid and benzimidazole groups reduced the water uptake and methanol uptake. The SPI membranes with ion exchange capacities (IECs) of 1.9–2.0 mequiv./g displayed reasonably high mechanical strength, thermal stability, water stability and proton conductivity. They showed anisotropic membrane swelling in water with 2.8 times larger swelling in thickness direction than in plane one and anisotropic proton conductivity with 25% smaller conductivity in thickness direction than in plane one. They suppressed methanol crossover in direct methanol fuel cell (DMFC) operation and displayed fairly high DMFC performances even at high methanol concentrations. The Faraday's efficiency and overall DMFC efficiency at 60 °C and 200 mA/cm 2 for SPI membrane with IEC of 1.9 mequiv./g were 75 and 23%, respectively, at 5 wt% methanol feed concentration and 39 and 10.2%, respectively, at 20 wt%. The SPI membranes have high potential for DMFC applications at mediate temperatures (40–80 °C).

Sulfonated polyimide hybrid membranes for polymer electrolyte fuel cell applications

Sulfonated Si-MCM-41 (SMCM) with an ion exchange capacity (IEC) of 2.3 mequiv. g −1 was used as a hydrophilic and proton-conductive inorganic component. Sulfonated polyimide (SPI) based on 1,4,5,8-naphthalene tetracarboxylic dianhydride and 2,2′-bis(3-sulfophenoxy) benzidine was used as a host membrane component. The SMCM/SPI hybrid membrane (H1) with 20 wt% loading of SMCM and an IEC of 1.90 mequiv. g −1 showed the high mechanical tensile strength and the slightly higher water vapor sorption than the host SPI membrane (M1) with an IEC of 1.86 mequiv. g −1. H1 and M1 showed anisotropic membrane swelling with about 10 times larger swelling in thickness direction than in plane one. The proton conductivity at 60 °C of H1 was lower in water than that of M1, but comparable at 30% RH. At 90 °C, H1 showed the rather lower performance of polymer electrolyte fuel cell (PEFC) at 82% RH than M1 and fairly better performance at 30% RH. On the other hand, at 110 °C and low humidity less than 50% RH, H1 showed the much better PEFC performance than M1 and Nafion 112. This was due to the promoted back diffusion of produced water by the superior water-holding capacity of SMCM. The SMCM/SPI hybrid membranes have high potential for PEFCs at higher temperatures and lower humidities.

Effects of tetracarboxylic dianhydrides on the properties of sulfonated polyimides

AbstractA series of sulfonated polyimides (SPIs) were synthesized from a sulfonated diamine of 4,4′‐bis(4‐aminophenoxy) biphenyl‐3,3′‐disulfonic acid (BAPBDS), common nonsulfonated diamines, and various tetracarboxylic dianhydrides including 1,4,5,8‐naphthalene tetracarboxylic dianhydride (NTDA), 3,4,9,10‐perylene tetracarboxylic dianhydride (PTDA), 4,4′‐binaphthyl‐1,1′,8,8′‐tetracarboxylic dianhydride (BTDA), 4,4′‐ketone dinaphthalene 1,1′,8,8′‐tetracarboxylic dianhydride (KDNTDA), and isophthatic dinaphthalene 1,1′,8,8′‐tetracarboxylic dianhydride (IPNTDA). Their membrane properties were investigated to clarify the effects of the dianhydrides. They displayed reasonably high mechanical properties, thermal stability, and proton conductivity. The dianhydrides with flexible and non‐coplanar structure (IPNTDA > KDNTDA > BTDA) led to the better solubility of the SPIs than those with rigid and coplanar one (NTDA, PTDA). The dianhydride with the smaller molecular weight led to the larger value of the number of sorbed water molecules per sulfonic acid group (λ) in membrane, that is, NTDA (λ: 17) > PTDA (15) > BTDA (14) > KDNTDA (12) > IPNTDA (10), and as a result let to the larger proton conductivity in water. All of the BAPBDS‐based SPIs showed the anisotropy in membrane swelling and in proton conductivity, of which the degree hardly depended on the dianhydride moieties. The water stability of SPI membranes against the aging in water at 130 °C for 192 h was in the order, PTDA = NTDA ≧ BTDA > KDNTDA > IPNTDA. The hydrolysis stability of polymer chain was similar between the BTDA‐ and KDNTDA‐based SPIs. These results are discussed. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 905–915, 2010

A new supramolecular sulfonated polyimide for use in proton exchange membranes for fuel cells

Uracil-terminated telechelic sulfonated polyimides (SPI-U) were transformed into noncovalent network membranes through biocomplementary hydrogen bonding recognition in the presence of an adenine-based crosslinking agent. SPI-U membrane exhibited dramatically improved methanol permeability, oxidative stability, proton conductivity, and selectivity relative to those of the standard SPI.