CHITOSAN-BASED FUEL CELL MEMBRANES

Chitosan complex membranes are prepared and characterized at room temperature. They are expected to be used as proton exchange membranes. The studied membranes are cross-linked membranes with sulfuric acid; salt-complexed membranes with lithium nitrate; cross-linked and salt-complexed membranes; plasticized and salt-complexed membranes; cross-linked, plasticized, and salt-complexed membranes; and doped membranes with sulfuric acid. A fixed amount of ethylene carbonate is used as plasticizer. It is found that the ion exchange capacity and hydrogen gas permeability of all membranes is better than that of Nafion membranes. However, their proton conductivities are worse than Nafion membranes. It can be stated that ethylene carbonate does not improve conductivity. An optimum amount of lithium nitrate salt can enhance conductivity. The formation of a sulfate group in cross-linked membranes is necessary for proton conduction. The proton conductivities of 4%cross-linked and 50%LiNO₃ membrane before and after acid doping are (3.11±0.40) × 10^-2 and (6.64±0.11) × 10^-2 S cm^-1, respectively. That of Nafion is (8.02±1.19) × 10^-2 S cm^-1.     

Proton-conducting membranes from phosphotungstic acid-doped sulfonated polyimide for direct methanol fuel cell applications

A series of novel hybrid proton conducting membranes based on sulfonated naphthalimides and phosphotungstic acid (PTA) were prepared from N-Methyl Pyrrolidone (NMP) solutions. These hybrid organic-inorganic materials, composed of two proton-conducting components, have high ionic conductivities (9.3 × 10^?2 S cm^?1 at 60 °C, 15% PTA), and show good performance in H₂|O₂ polymer electrolyte membrane fuel cells (PEMFC), previously reported by us. Moreover, they have low methanol permeability compared to Nafion^®112. In this paper we describe, for the first time, the behaviour of these hybrid membranes as electrolyte in a direct methanol fuel cell (DMFC). The maximum power densities achieved with PTA doped sulfonated naphthalimide membrane, operating with oxygen and air, were 34.0 and 12.2 mW cm^?2, respectively; about the double and triple higher than those showed by the non-doped membrane at 60 °C.     

Phthalonitrile end-capped sulfonated polyarylene ether nitriles for low-swelling proton exchange membranes

A series of phthalonitrile end-capped sulfonated polyarylene ether nitriles are synthesized via K₂CO₃ mediated nucleophilic aromatic substitution reaction at various molar ratios. The as-prepared polymer structures are confirmed by ¹H NMR and FTIR spectroscopy. The properties of membranes cast from the corresponding polymers are investigated with respect to their structures. The membranes exhibit good thermal and mechanical properties, low methanol permeability (0.01?×?10^?6–0.58?×?10^?6 cm²·s^?1 at 20 °C), and high proton conductivity (0.021–0.088 S·cm^?1 at 20 °C). The introduction of phthalonitrile is proved to increase intermolecular interaction, mainly contributing to the reduction in water uptake, swelling ratio, and methanol permeability. More importantly, its introduction does not decrease the proton conductivity, but there is a slight increase. Furthermore, the selectivity of SPEN-CN-50 can reach 4.11?×?10⁵ S·s·cm^?3, which is about nine times higher than that of Nafion 117. All the data show that the as-prepared membranes may be potential proton exchange membrane for DMFCs applications.     

Impact of hydroquinone on thermal and electrical properties of plasticized [poly(vinyl alcohol)]0.7(LiBr)0.3(H2SO4) solid acid membrane

A novel multi‐component system containing poly(vinyl alcohol), lithium bromide, sulfuric acid, ethylene carbonate and hydroquinone was prepared using a solution‐casting technique. The presence of hydroquinone as a reducing agent in the inorganic–organic membrane structure thus produced was thought to lead to enhanced thermal stability of the membrane. The activation energy for the thermal decomposition of the product samples increased with increasing hydroquinone doping. The ionic conductivities of the films were determined from AC impedance measurements in the temperature range 300–373 K. The maximum conductivity was found to be 1.75 × 10^?3 S cm^?1 for a film doped with 4 wt% hydroquinone. The results give some insight into the potential utility of the membrane as a proton‐conducting solid polymer electrolyte. Copyright © 2011 Society of Chemical Industry     

Proton exchange membrane based on crosslinked sulfonated polyphosphazene containing pendent perfluorosulfonic acid groups with sulfonated poly(ether ether ketone)

A series of crosslinked membranes based on new sulfonated polyphosphazene bearing pendent perfluorosulfonic acid groups (PMFP‐g‐PS) and sulfonated poly (ether ether ketone) were prepared and evaluated as proton exchange membranes for direct methanol fuel cells (DMFCs). The structure of PMFP‐g‐PS was characterized by Fourier transform infrared spectroscopy, ¹H and ¹⁹F NMR spectra. In comparison with the pristine PMFP‐g‐PS membrane, the crosslinked membranes showed improved water uptakes and proton conductivities. The methanol permeability values of the membranes were in the range of 1.32 × 10^?7 to 3.85 × 10^?7 cm²/s, which were lower than Nafion 117 (12.1 × 10^?7 cm²/s). The selectivity of all the membranes was much higher compared with Nafion 117. Furthermore, transmission electron microscopy observation revealed that clear phase‐separated structures were well dispersed and connected to each other in the membranes. These membranes displayed high water uptakes and low swelling ratios, high proton conductivities, low methanol permeability values, good thermal, and oxidative stabilities. The results indicate that these membranes are potential candidate proton exchange membrane materials for DMFCs. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43492.     

Influence of Sulfonated Graphene Oxide on Sulfonated Polysulfone Membrane for Direct Methanol Fuel Cell

Novel proton exchange membranes consisting of an inorganic filler, namely sulfonated graphene oxide, embedded in sulfonated polysulfone were fabricated. The membrane performance depended on the sulfonated graphene oxide content possessed the functional groups to provide the interfacial interaction with sulfonated polysulfone through ionic channels and blocking effect. The membrane with 3% v/v sulfonated graphene oxide content embedded in the matrix was shown to be suitable for direct methanol fuel cell applications. The membrane exhibited the highest proton conductivity of 4.27?×?10^?3 S cm^?1 which was higher than that of Nafion117. Moreover, the membrane provided the lowest methanol permeability of 3.48?×?10^?7?cm²/s which was lower than that of Nafion117.     

Preparation and properties of bisphenol A‐based sulfonated poly(arylene ether sulfone) proton exchange membranes for direct methanol fuel cell

Novel bisphenol A‐based sulfonated poly(arylene ether sulfone) (bi A‐SPAES) copolymers were successfully synthesized via direct copolymerization of disodium 3,3′‐disulfonate‐4,4′‐dichlorodiphenylsulfone, 4,4′‐dichlorodiphenylsulfone, and bisphenol A. The copolymer structure was confirmed by Fourier transform infrared spectra and ¹H NMR analysis. The series of sulfonated copolymers based membranes were prepared and evaluated for proton exchange membranes (PEM). The membranes showed good thermal stability and mechanical property. Transmission electron microscopy was used to obtain the microstructures of the synthesized polymers. The membranes exhibit increased water uptake from 8% to 66%, ion exchange capacities from 0.41 to 2.18 meq/g and proton conductivities (25°C) from 0.012 to 0.102 S/cm with the degree of sulfonation increasing. The proton conductivities of bi A‐SPAES‐6 membrane (0.10–0.15 S/cm) with high‐sulfonated degree are higher than that of Nafion 117 membrane (0.095–0.117 S/cm) at all temperatures (20–100°C). Especially, the methanol diffusion coefficients of membranes (1.7 × 10^?8 cm²/s–8.5 × 10^?7 cm²/s) are much lower than that of Nafion 117 membrane (2.1 × 10^?6 cm²/s). The new synthesized copolymer was therefore proposed as a candidate of material for PEM in direct methanol fuel cell. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

New organic–inorganic hybrid membranes based on sulfonated polyimide/aminopropyltriethoxysilane doping with sulfonated mesoporous silica for direct methanol fuel cells

A series of novel composite methanol‐blocking polymer electrolyte membranes based on sulfonated polyimide (SPI) and aminopropyltriethoxysilane (APTES) doping with sulfonated mesoporous silica (S‐mSiO₂) were prepared by the casting procedure. The microstructure and properties of the resulting hybrid membranes were extensively characterized. The crosslinking networks of amino silica phase together with sulfonated mesoporous silica improved the thermal stability of the hybrid membranes to a certain extent in the second decomposition temperature (250–400°C). The composite membranes doping with sulfonated mesoporous silica (SPI/APTES/S‐mSiO₂) displayed superior comprehensive performance to the SPI and SPI/APTES membranes, in which the homogeneously embedded S‐mSiO₂ provided new pathways for proton conduction, rendered more tortuous pathways as well as greater resistance for methanol crossover. The hybrid membrane with 3 wt % S‐mSiO₂ into SPI/APTES‐4 (SPI/A‐4) exhibited the methanol permeability of 4.68 × 10^?6 cm² s^?1at 25°C and proton conductivity of 0.184 S cm^?1 at 80°C and 100%RH, while SPI/A‐4 membrane had the methanol permeability of 5.16 × 10^?6 cm² s^?1 at 25°C and proton conductivity of 0.172 S cm^?1 at 80°C and 100%RH and Nafion 117 exhibited the values of 8.80 × 10^?6 cm² s^?1 and 0.176 S cm^?1 in the same test conditions, respectively. The hybrid membranes were stable up to about 80°C and demonstrated a higher ratio of proton conductivity to methanol permeability than that of Nafion117. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Sulfonated poly(bis‐A)‐sulfones as proton exchange membranes for direct methanol fuel cell application

Sulfonated poly(bis‐A)‐sulfone (SPSF) samples were prepared by a mild postsulfonation method using trimethylsilyl chlorosulfonate as sulfonation agent, and their thermal and mechanical properties were evaluated. The serials of SPSF membranes are thermally stable up to 450°C in air. When compared with the poly(bis‐A)‐sulfone membrane, the hydrophilicity and water uptake of the SPSF membranes are enhanced. A microphase‐separated structure comprised of hydrophilic and hydrophobic polymer backbone was observed from atomic force microscopy phase images. The hydrophilic ionic clusters become continuous to form channels when ion exchange capacity (IEC) reached 1.47 mequiv/g. Moreover, the membranes showed very good proton conductivities (20°C, 0.01–0.11 S/cm) and low‐methanol permeability (0.09–3.06 × 10^?6 cm²/s), and the methanol diffusion coefficients were lower than that of Nafion112 (1.35 × 10^?6 cm²/s) with IEC values from 0.70 to 1.47 mequiv/g. However, the Fenton's reagent test revealed that the membranes exhibited very poor oxidation stability, which is the main defect limiting the application of SPSF for proton exchange membranes. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers     

Synthesis and characterization of sulfonated poly(ether sulfone ether ketone ketone) for proton exchange membranes

A series of sulfonated poly(ether sulfone ether ketone ketone) (SPESEKK) with different degree of sulfonation (DS) are prepared by the postsulfonation of PESEKK using chlorosulfonic acid as sulfonating agent and concentrated sulfuric acid as solvent. The chemical structures of the polymers are analyzed by the proton nuclear magnetic resonance. The thermal properties of the SPESEKK show that they are greatly influenced by the DS value and sulfonation time. The water uptake, proton conductivity, and Ion exchange capacity values increase as the sulfonation time increasing. The methanol permeability of the SPESEKK in the range of 7.02 × 10^?8 to 4.477 × 10^?7 cm² s^?1, is one or two orders of magnitude lower than that of Nafion 115. The morphology of the SPESEKK membranes is investigated by scanning electron microscope. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

A novel heteropolyacid-doped carbon nanotubes/Nafion nanocomposite membrane for high performance proton-exchange methanol fuel cell applications

A novel proton-exchange polymer composite membrane was synthesized using Nafion^®, tetraethoxysilane-modified carbon nanotubes (CNTs) and phosphotungstic acid-modified carbon nanotubes with the aim of using direct methanol fuel cells (DMFCs). Physicochemical properties of the modified CNTs and fabricated composite membranes were investigated by Fourier transform infrared spectroscopy, field emission scanning electron microscopy, water uptake, thermogravimetric analysis, ion exchange capacity, proton conductivity and methanol permeability tests. It was demonstrated that chemical surface modification of CNTs and introduction of the phosphotungstic acid (PWA) groups effectively improved the performance of DMFC. It was found that the presence of PWA groups on the surface of CNTs led to the formation of strong electrostatic interactions between the PWA groups and clusters of sulfonic acid in Nafion^® macromolecules. Hence, the incorporation of inorganic phosphotungstic super-acid-doped silicon oxide-covered carbon nanotubes (CNT@SiO₂-PWA) into Nafion^® matrices enhanced the proton conductivity of the prepared membranes. Moreover, the methanol permeability was reduced to 2.63 × 10^?7 cm² s^?1 in comparison with the recast Nafion^® membrane (2.25 × 10^?6 cm² s^?1). Enhancing the proton conductivity and reducing the methanol permeability, the selectivity of the prepared nanocomposite membranes was enhanced to a greater value of 330,700 S s cm^?3 as compared to the value of 38,222 S s cm^?3 for recast Nafion^®.     

A quaternized poly(vinyl alcohol)/chitosan composite alkaline polymer electrolyte: preparation and characterization of the membrane

Quaternized poly(vinyl alcohol)/chitosan (QPVA/CS) composite membranes were prepared by solution casting method with AlCl₃·6H₂O aqueous solution as solvent for CS and glutaraldehyde as a crosslinker. The crystalline, thermal and mechanical properties of the QPVA/CS composite membranes were studied by Fourier transform infrared spectroscopy, X-ray diffractometry, differential scanning calorimetry, thermogravimetry and tensile test measurements, respectively. The composite membranes were immersed in potassium hydroxide aqueous solution to form polymer electrolyte membranes. The alkaline uptake, swelling ratio, ion conductivity and methanol permeability of the electrolyte membranes were studied. The experimental results indicated that aluminum chloride hexahydrate (AlCl₃·6H₂O) had a positive effect on the mechanical properties of the QPVA/CS composite membrane. The elongation-at-break of this membrane reached the maximum of 401.0%. The alkaline uptake and swelling ratio of the composite membranes decreased. With the addition of 30 wt% AlCl₃·6H₂O, the composite membrane showed the ion conductivity and methanol permeability of 1.82 × 10^?2 S cm^?1 and 2.17 × 10^?6 cm² s^?1, respectively. These values were higher than those of the membrane with acetic acid as the solvent for CS. The selectivity of the QPVA/CS membrane could reach 8.39 × 10³ S s cm^?3. This study showed that with AlCl₃·6H₂O as the solution for CS, the high performance QPVA/CS composite alkaline polymer electrolyte membrane could be prepared.     

Sulfonated copoly(norbornene)s bearing sultone pendant groups and application as proton exchange membranes candidates

Novel copolynorbornenes bearing pendant sultone groups (designated as P(BN/SulNBOH) and P(BN/SulNBOMe)) have been successfully synthesized via copolymerization of functionalized norbornenes bearing sultones (designated as SulNBOH and SulNBOMe) with 2-butoxymethylene norbornene (BN). The catalyst system showed high catalyst activity (10⁴ g_polymer/mol_Ni·h) and the obtained copolymers have high molecular weight and a narrow molecular weight distribution. Furthermore, the achieved copolymers P(BN/SulNBOH) and P(BN/SulNBOMe) were converted into sulfonated copolymers sP(BN/NBOH) and sP(BN/NBOMe). Both sP(BN/NBOH) and sP(BN/NBOMe) membranes displayed low water uptake, high thermal properties, good mechanical properties, and better proton exchange membranes properties. The proton conductivities measured in the hydrated state at 80?°C ranged from 10^?5 to 7.19?×?10^?3?S·cm^?1.

Synthesis and characterization of acid–base polyimides bearing pendant sulfoalkoxy groups for direct methanol fuel cell applications

A series of acid–base polyimides with sulfonic acid groups in the side chains have been prepared, based on a new synthesized sulfonated diamine monomer containing pyridine functional group. The effect of the introduction of pyridine groups into copolymer backbone on the properties of membrane were evaluated through the investigation of membrane parameters. The copolymers produced flexible, tough, and transparent membranes by solvent casting method. All the prepared membranes displayed high thermal stability, great oxidative stability and good mechanical properties. They exhibited appropriate water uptake (15.8–30.2 wt % at 80°C) and remarkable dimensional stability (2.5–6.9% at 80°C). The proton conductivity of SPI‐80 was 1.01 × 10^?2 S cm^?1 at room temperature. Moreover, the methanol permeability of SPI‐80 membrane was 1.22 × 10^?7 cm² s^?1, which was lower than 23.8 × 10^?7 cm² s^?1 of Nafion 117. Therefore, these acid‐base polyimides materials have a promising prospect for direct methanol fuel cell applications. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42238.     

Zeolite Proton Conducting Membrane for Micro Fuel Cell Applications

Supported and self-supporting ZSM-5 membranes (Si/Al = 25) were prepared, assembled and tested for hydrogen fuel cell performance. A Grotthus-like mechanism is proposed for the proton conduction in hydrated zeolites, where the protons hop between neighbouring aluminium sites along a water bridge in the zeolite pores. The supported ZSM-5 membrane was prepared by seeding and secondary regrowth method on cellulose paper, whereas the self-supporting zeolite membrane consists of an array of micromembranes on silicon substrate. The self-supporting HZSM-5 membrane had an open-circuit voltage (OCV) of 0.77 V compared to 0.90 V for supported HZSM-5 and 0.98 V for Nafion 117. The differences are attributed to the contact between the electrode, catalyst and membrane layers in the assembly. The self-supporting HZSM-5 yielded a maximum power density (MPD) of 19.4 mW cm^?2 compared to 14.4 mW cm^?2 for supported HZSM-5 and 35 mW cm^?2 for Nafion 117.     

Blends of Poly(ether imide) and Styrene Sulfonic Acid Based Polymer: Thermal,Mechanical and Ionic Conduction Behavior

Dense membranes based on poly(ether imide) (PEI) and poly(styrene sulfonic acid-co-maleic acid) (PSSAMA) was obtained by extrusion and compression molding. Blends with different PSSAMA content (1, 3, 5, and 10 wt%) were prepared. Their morphology was investigated by scanning electron microscopy (SEM) and their thermal properties by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and dynamic-mechanical analysis (DMA). Two glass transition temperatures (T_g) (100 and 216°C) appeared when high contents of PSSAMA were added to PEI, indicating that the polymers form an immiscible system. TGA curves showed that the first weight loss occurred above 400°C for all blends, indicating a good thermal stability. Water uptake measurements have shown that the membranes presented low swelling when compared with Nafion®. The proton conductivity of the membrane with 10 wt% of PSSAMA obtained bv impedance measurements was 0.006 × 10^?2 S·cm^?1.     

Sulfonated (graphene oxide/poly(ether ketone ether sulfone) (S-GO/S-PEKES) composite proton exchange membrane with high proton conductivity for direct methanol fuel cell

ABSTRACT

Sulfonated poly(ether ketone ether sulfone) (S-PEKES) was successfully prepared to obtain the currently highest degree of sulfonation of 0.744. Sulfonated graphene oxide (S-GO) was incorporated into the S-PEKES matrix to increase sulfonic groups (SO₃H) which significantly improved the proton conductivity, methanol blocking, and mechanical stability. The proton conductivity of the S-GO/S-PEKES composite membrane was enhanced up to 5.93 × 10^?2 S.cm^?1, which was 7 times higher than the commercial Nafion 117. S-GO exhibited additional positive effects namely the blocking of methanol passing through the membrane, leading to lower methanol crossover than Nafion 117 by two orders of magnitude and high mechanical stability.     

Poly(vinyl alcohol)–polyacrylamide blends with cesium salts of heteropolyacid as a polymer electrolyte for direct methanol fuel cell applications

A class of inorganic–organic hybrid membranes with low methanol permeability characteristics for possible direct methanol fuel cell (DMFC) applications was architected, formulated, and fabricated through the blending of poly(vinyl alcohol) (PVA) and polyacrylamide (PAM) followed by crosslinking with glutaraldehyde (Glu). Cesium salts of different heteropolyacids, including phosphomolybdic acid (PMA), phosphotungstic acid (PWA), and silicotungstic acid (SWA), were incorporated into the polymer network to form corresponding hybrid membrane materials, namely, PVA–PAM–CsPMA–Glu, PVA–PAM–CsPWA–Glu, and PVA–PAM–CsSWA–Glu, respectively (where “Cs” together with a heteropolyacid abbreviation indicates the cesium salt of that acid). All the three hybrid polymer membranes fabricated exhibited excellent swelling, thermal, oxidative, and additive stability properties with desired proton conductivities in the range 10^?2 S/cm at 50% relative humidity. A dense network formation was achieved through the blending of PVA and PAM and by crosslinking with Glu, which led to an order of magnitude decrease in the methanol permeability compared to the state‐of‐the‐art commercial Nafion 115 membrane. The hybrid membrane containing CsSWA exhibited a very low methanol permeability (1.4 × 10^?8 cm²/s) compared to other membranes containing cesium salt of heteropolyacids such as PMA and PWA. The feasibility of these hybrid membranes as proton‐conducting electrolytes in DMFC was investigated, and the preliminary results were compared with those of Nafion 115. The results illustrate the attractive features and suitability of the fabricated hybrid membranes as an electrolyte for DMFC applications. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Preparation and characterization of proton exchange membrane based on polyphosphoric acid modified by PVDF‐HFP

A polyphosphoric acid functionalized proton exchange membrane (PEM) was prepared by a ring opening reaction using the epoxycyclohexylethyltrimethoxysilane (EHTMS) and amino trimethylene phosphonic acid (ATMP) as raw materials and was modified by poly(vinylidene fluoride)–hexafluoro propylene (PVDF‐HFP). The structure of the membranes was characterized by Fourier transform infrared and scanning electron microscopy. The X‐ray photoelectron spectroscopy explores the content of the elements in the membrane related to the ion exchange capacity value. The membranes’ properties including water uptake, swelling ratio, proton conductivity, and hydrolysis stability were studied. Performance tests show that when ATMP/EHTMS = 1/5, conductivity of the PVDF‐HFP modified PEMs increased from 0.83 × 10^?4 S cm^?1 at 20 °C to 9.53 × 10^?3 S cm^?1 at 160 °C, the swelling ratio of membranes decreased from 2.71% to 2.13%. The results indicate that the introduction of F atoms is beneficial to increase the proton conductivity and the dimensional stability. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46737.     

Synthesis and Characterization of Sulfonated Cardo Poly(Arylene Ether Sulfone)s for Fuel Cell Proton Exchange Membrane Application

Sulfonated cardo poly(arylene ether sulfone)s ( SPPA ‐ PES ) with various degrees of sulfonation (DS) were prepared by post‐sulfonation of synthesized phenolphthalein anilide ( PPA ; N‐phenyl‐3,3′‐bis(4‐hydroxyphenyl)‐1‐isobenzopyrolidone) poly(arylene ether sulfone)s ( PPA ‐ PES ) by using concentrated sulfuric acid. PPA ‐ PES copolymers were synthesized by direct polycondensation of PPA with bis‐(4‐fluorophenyl)‐sulfone and 4,4′‐sulfonyldiphenol. The DS was varied with different mole ratios of PPA (24, 30, 40, 50 mol.%) in the polymer. The structure of the resulting SPPA ‐ PES copolymers and the different contents of the sulfonated unit were studied by Fourier transform infrared (FT‐IR) spectroscopy, ¹H NMR spectroscopy, and thermogravimetric analysis (TGA). Sorption experiments were conducted to observe the interaction of sulfonated polymer with water. The ion exchange capacity (IEC) and proton conductivity of SPPA ‐ PES were evaluated according to the increase of DS. The water uptake (WU) of the resulting SPPA ‐ PES membranes was in the range of 20–72%, compared with 28% for Nafion 211®. The SPPA ‐ PES membranes showed proton conductivities of 23–82 mS cm^–1, compared with 194 mS cm^–1 for Nafion 211®, under 100% relative humidity (RH) at 80 °C.