Novel membranes based on poly(5‐(methacrylamido)tetrazole) and sulfonated polysulfone for proton exchange membrane fuel cells

Proton‐exchange membrane fuel cells (PEMFC)s are increasingly regarded as promising environmentally benign power sources. Heterocyclic molecules are commonly used in the proton conducting membranes as dopant or polymer side group due to their high proton transfer ability. In this study, 5‐(methacrylamido)tetrazole monomer, prepared by the reaction of methacryloyl chloride with 5‐aminotetrazole, was polymerized via conventional free radical mechanism to achieve poly(5‐(methacrylamido)tetrazole) homopolymer. Novel composite membranes, SPSU‐PMTetX, were successfully produced by incorporating sulfonated polysulfone (SPSU) into poly(5‐(methacrylamido)tetrazole) (PMTet). The sulfonation of polysulfone was performed with trimethylsilyl chlorosulfonate and high degree of sulfonation (140%) was obtained. The homopolymers and composite membranes have been characterized by NMR, FTIR, thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). ¹H‐NMR and FTIR confirmed the sulfonation of PSU and the ionic interaction between sulfonic acid and poly(5‐(methacrylamido)tetrazole) units. TGA showed that the polymer electrolyte membranes are thermally stable up to ～190°C. Scanning electron microscopy analysis indicated the homogeneity of the membranes. This result was also supported by the appearance of a single T_g in the DSC curves of the blends. Water uptake and proton conductivity measurements were, as well, carried out. Methanol permeability measurements showed that the composite membranes have similar methanol permeability values with Nafion 112. The maximum proton conductivity of anhydrous SPSU‐PMTet0.5 at 150°C was determined as 2.2 × 10^?6 S cm^?1 while in humidified conditions at 20°C a value of 6 × 10^?3 S cm^?1 was found for SPSU‐PMTet2. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40107.     

Synthesis and proton conductivity studies of 5‐aminotetrazole‐doped sulfonated polymer electrolyte membranes

This work reports the preparation and characterization of a new anhydrous proton conducting membrane based on poly(vinyl alcohol) (PVA), sulfosuccinic acid (SSA), and 5‐aminotetrazole (ATet) at various stoichiometric ratios. The proton conductivities of membranes were investigated as a function of ATet composition, SSA composition, and temperature. New anhydrous proton conducting membranes were characterized by infrared spectra, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), methanol permeability, and impedance measurements for proton conductivity. TGA showed that the samples were thermally stable up to 150°C. DSC results illustrated the homogeneity of the materials. Mechanical analysis showed that the storage modulus of the PVA–SSA–ATet blend polymer membranes decreased with increasing ATet content. The membranes with higher tetrazole content, or higher acid doping level presented the higher proton conductivity. PVA–SSA–ATet4 can exhibit an anhydrous proton conductivity of 1.7 × 10⁻³ S/cm at 130°C and the proton conductivity increased with increasing temperature and acid doping level. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Proton conducting polymer blends from poly(2,5‐benzimidazole) and poly(2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid)

Proton conducting polymer electrolyte membranes were produced by blending of poly(2,5‐benzimidazole) (ABPBI) and poly(2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid) (PAMPS) at several stoichiometric ratios with respect to polymer repeating units. The membranes were characterized by using Fourier transform infrared spectroscopy for interpolymer interactions and scanning electron microscope for surface morphology. Thermal stability of the materials was investigated by thermogravimetric analysis. Glass transition temperatures of the samples were measured via differential scanning calorimetry. The spectroscopic measurements and water uptake studies indicate a complexation between ABPBI and PAMPS that inhibited polymer exclusion up on swelling in excess water. Proton conductivities of the anhydrous and humidified samples were measured using impedance spectroscopy. The proton conductivity of the humidified ABPBI:PAMPS (1 : 2) blend showed a proton conductivity of 0.1 S/cm, which is very close to Nafion 117, at 20°C at 50% relative humidity. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Proton conducting properties of ionically cross-linked poly(1-vinyl-1,2,4 triazole) and poly(2-acrylamido-2-methyl-1-propanesulfonic acid) electrolytes

The synthesis and thermal as well as proton conducting properties of complex polymer electrolytes based on poly(2-acrylamido-2-methyl-1-propanesulfonic acid) PAMPS and poly(1-vinyl-1,2,4-triazole) PVTri were investigated. The materials were produced by complexation of PAMPS with PVTri at various compositions to get PVTriP(AMPS) _x where x is the molar ratio of the polymer repeating units and varied from 0.25 to 4. The structure of the materials was confirmed by FT-IR spectroscopy. The TGA results verified that the polymer electrolytes are thermally stable up to approximately 200 °C. The DSC and SEM results demonstrated the homogeneity of the materials. The electrochemical stability of the materials was studied by cyclic voltammeter (CV). Proton conductivity, activation energy, and water/methanol uptake of these membranes were also measured. After humidification (RH = 50%), PVTriP(AMPS)₂ and PVTriP(AMPS)₄ showed proton conductivities of 0.30 and 0.06 S/cm at 100 °C, respectively.     

Synthesis and characterization of poly(ether sulfone) grafted poly(styrene sulfonic acid) for proton conducting membranes

Two-step synthesis of proton-conducting poly(ether sulfone) (PES) graft copolymer electrolyte membrane is proposed. Fridel Craft alkylation reaction was used to introduce chloromethyl pendant group onto the PES polymer backbone. Later on, atom transfer radical polymerization (ATRP) was applied to synthesize a series of poly(ether sulfone) grafted poly(styrene sulfonic acid) (PES-g-PSSA). Successful chloromethyl substitution and grafting of the pendant group was characterized by the ¹H-NMR and elemental analysis. Electrochemical properties such as ion exchange capacity (IEC), water uptake and proton conductivity increased with increasing PSSA contents. Thermal gravimetric analysis (TGA) showed the thermal stability of membranes up to 270 °C. Proton conductivity for maximum amount of grafting was 0.00297 S/cm.     

PWA/silica doped sulfonated poly(ether sulfone) composite membranes for direct methanol fuel cells

A novel sulfonated poly(ether sulfone) (SPES)/phosphotungstic acid (PWA)/silica composite membranes for direct methanol fuel cells (DMFCs) application were prepared. The structure and performance of the obtained membranes were characterized by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), water uptake, proton conductivity, and methanol permeability. Compared to a pure SPES membrane, PWA and SiO₂ doped membranes had a higher thermal stability and glass transition temperature (T_g) as revealed by TGA‐FTIR and DSC. The morphology of the composite membranes indicated that SiO₂ and PWA were uniformly distributed throughout the SPES matrix. Proper PWA and silica loadings in the composite membranes showed high proton conductivity and sufficient methanol permeability. The selectivity (the ratio of proton conductivity to methanol permeability) of the SPES‐P‐S 15% composite membrane was almost five times than that of Nafion 112 membrane. This excellent selectivity of SPES/PWA/silica composite membranes indicate a potential feasibility as a promising electrolyte for DMFC. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis and Characterization of a New Fluorine‐Containing Polybenzimidazole (PBI) for Proton‐Conducting Membranes in Fuel Cells

A new type of fluorine‐containing polybenzimidazole, namely poly(2,2′‐(2,2′‐bis(trifluoromethyl)‐4,4′‐biphenylene)‐5,5′‐bibenzimidazole) (BTBP‐PBI), was developed as a candidate for proton‐conducting membranes in fuel cells. Polymerization conditions were experimentally investigated to achieve high molecular weight polymers with an inherent viscosity (IV) up to 1.60 dl g^–1. The introduction of the highly twisted 2,2′‐disubstituted biphenyl moiety into the polymer backbone suppressed the polymer chain packing efficiency and improved polymer solubility in certain polar organic solvents. The polymer also exhibited excellent thermal and oxidative stability. Phosphoric acid (PA)‐doped BTBP‐PBI membranes were prepared by the conventional acid imbibing procedure and their corresponding properties such as mechanical properties and proton conductivity were carefully studied. The maximum membrane proton conductivity was approximately 0.02 S cm^–1 at 180 °C with a PA doping level of 7.08 PA/RU. The fuel cell performance of BTBP‐PBI membranes was also evaluated in membrane electrode assemblies (MEA) in single cells at elevated temperatures. The testing results showed reliable performance at 180 °C and confirmed the material as a candidate for high‐temperature polymer electrolyte membrane fuel cell (PEMFC) applications.     

Study of hyperbranched poly(glycidol) sulfate electrolyte

Hyperbranched poly(glycidol) alkali sulfate (SHPG‐M) was prepared based on hyperbranched poly(glycidol). Polyurethane–hyperbranched poly(glycidol) (PU–SHPG‐M) sulfate electrolyte is a kind of single ionic or cationic conducting polymer electrolyte. Such a single ionic polymer electrolyte can obviously reduce the polarization and has little decay of direct current (DC) conductivity. SHPG‐M was characterized by Fourier transform infrared (FTIR), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), atomic force microscopy (AFM) and impedance analysis. The optimum conductivity is ～3 × 10^?6 S·cm^?1, with 30–40% SHPG‐M in the polymer electrolyte at room temperature. The species of cation greatly effects the ionic conductivity of the polymer electrolyte; that is, σ_SHPG‐Li > σ_SHPG‐Na > σ_SHPG‐K, with same SHPG‐M content in the polymer electrolyte. The ionic conductivity increases with an increase of temperature, and the dependence of ionic conductivity on temperature fits the Arrhenius equation well. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1185–1190, 2003     

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     

Novel sulfonated poly(arylene biphenylsulfone ether) copolymers containing bisphenylsulfonyl biphenyl moiety: structural,thermal, electrochemical and morphological characteristics

A series of sulfonated poly(arylene biphenylsulfone ether) polymers containing up to two pendant sulfonic acid groups per repeat unit were successfully synthesized from 4,4′‐bis[(4‐chlorophenyl)sulfonyl]‐1,1′‐biphenyl (BCPSBP), disodium 3,3′‐disulfonate‐4,4′‐dichlorodiphenylsulfone (SDCDPS) and bisphenol A via aromatic nucleophilic displacement polycondensation. The resulting polymers were characterized by means of Fourier transform infrared and ¹H NMR spectroscopy, gel permeation chromatography, differential scanning calorimetry and thermogravimetric analysis (TGA). The number‐average molecular weight (M_n) of the synthesized polymers was in the range 15 300–22 900 g mol^?1, and the polydispersity indices (M_w/M_n) varied from 2.5 to 4.4. Tough membranes with SDCDPS/BCPSBP mole ratio up to 50:50 were successfully cast using N‐methyl‐2‐pyrrolidone (NMP). An increase of sulfonic acid groups in the polymer backbone resulted in increased solubility in aprotic polar solvents and glass transition temperature. The TGA curves of all the copolymers in acid form exhibited two distinct weight‐loss profiles. The influential characteristics of the polymer electrolyte membranes, such as tensile strength, water uptake, ion‐exchange capacity and proton conductivity, were characterized with respect to the pendant sulfonic acid groups. Atomic force microscopy phase images of the acid‐form membranes clearly showed the hydrophilic domains, with sizes increasing as a function of the degree of sulfonation. Copyright © 2010 Society of Chemical Industry     

Sulfonated poly(ether ether sulfone) copolymers for proton exchange membrane fuel cells

Novel aromatic sulfonated poly(ether ether sulfone)s (SPEESs) with tert‐butyl groups were synthesized by aromatic nucleophilic polycondensation of disodium 3,3′‐disulfonate‐4,4′‐dichlorodiphenylsulfone (SDCDPS), 4,4′‐dichlorodiphenylsulfone (DCDPS), and tert‐butylhydroquinone (TBHQ). The resulting copolymers showed very good thermal stability and could be cast into tough membranes. The morphology of the membranes was investigated with atomic force microscopy. The proton conductivity of SPEES‐40 membranes increased from 0.062 S/cm at 25°C to 0.083 S/cm at 80°C, which was higher than the 0.077 S/cm of Nafion 117 under the same testing conditions. These copolymers are good candidates to be new polymeric electrolyte materials for proton exchange membrane fuel cells. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1443–1450, 2007     

EB‐crosslinked Polymer Electrolyte Membranes Based on Highly Sulfonated Poly(ether ether ketone) and Poly(vinylidene fluoride)/Triallyl Isocyanurate

In this study, crosslinked polymer electrolyte membranes for polymer electrolyte membrane fuel cell (PEMFC) applications are prepared using electron beam irradiation with a mixture of sulfonated poly(ether ether ketone) (SPEEK), poly(vinylidene fluoride) (PVDF), and triallyl isocyanurate (TAIC) at a dose of 300 kGy. The gel‐fraction of the irradiated SPEEK/PVDF/TAIC (95/4.5/0.5) membrane is 87% while the unirradiated membrane completely dissolves in DMAc solvent. In addition, the water uptake of the irradiated membrane is 221% at 70 °C while that of the unirradiated membrane completely dissolves in water at above 70 °C. The ion exchange capacity and proton conductivity of the crosslinked membrane are 1.57 meq g⁻¹, and 4.0 × 10⁻² S cm⁻¹ (at 80 °C and RH 90%), respectively. Furthermore, a morphology study of the membranes is conducted using differential scanning calorimetry and X‐ray diffractometry. The cell performance study with the crosslinked membrane demonstrates that the maximum power density is 518 mW cm⁻² at 1036 mA cm⁻² and the maximum current density at applied voltage of 0.4 V is 1190 mA cm⁻².     

Salt‐leaching technique for the synthesis of porous poly(2,5‐benzimidazole) (ABPBI) membranes for fuel cell application

The first instance of synthesizing porous poly(2,5‐benzimidazole) (ABPBI) membranes for high‐temperature polymer electrolyte membrane fuel cells (HT‐PEMFCs), using solvent evaporation/salt‐leaching technique, is reported herein. Various ratios of sodium chloride/ABPBI were dissolved in methanesulfonic acid and cast into membranes by solvent evaporation, followed by porogen (salt) leaching by water washing. The membranes were characterized using SEM, FTIR, TGA, and DSC. The proton conductivity, water and acid uptake of the membranes were measured and the chemical stability was determined by Fenton's test. SEM images revealed strong dependence of sizes and shapes of pores on the salt/polymer ratios. Surface porosities of membranes were estimated with Nis Elements‐D software; bulk porosities were measured by the fluid resaturation method. Thermogravimetric analysis showed enhanced dopant uptake with introduction of porosity, without the thermal stability of the membrane compromised. Incorporating pores enhanced solvent uptake and retention because of capillarity effects, enhancing proton conductivities of PEMs. Upon acid doping, a maximum conductivity of 0.0181 S/cm was achieved at 130 °C for a porous membrane compared with 0.0022 S/cm for the dense ABPBI membrane at the same temperature. Results indicated that with judicious optimization of porogen/polymer ratios, porous ABPBI membranes formed by salt‐leaching could be suitably used in HT‐PEMFCs. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45773.     

Development and characterization of homogeneous membranes prepared from sulfonated poly(phenylene oxide)

This article investigates the comprehensive properties of sulfonated poly(phenylene oxide) (SPPO) membranes with different sulfonation degrees and presents the completion of previous work necessary for the application of SPPO membranes to proton‐exchange membrane fuel cells. The sulfonation level has been accurately determined by conductometric titration and ¹H‐NMR, and the glass‐transition temperature has been obtained with both differential scanning calorimetry and dynamic mechanical thermal analysis. Sulfonic groups attached to the aromatic ring in the poly(phenylene oxide) backbone split at 220–340°C, but the main‐chain splitting temperature of SPPO is similar to that of the pure polymer. In addition, the effects of sulfonic groups and water on the tensile strength of these membranes have been studied. An increase in the sulfonate groups in the polymer results in an increase in the water uptake. Atomic force microscopy phase images of the acid‐form membranes clearly show the hydrophilic domains, and the ionic regions of the membranes with a low sulfonation degree are isolated and become connected to produce a cocontinuous morphology as the degree of sulfonation increases. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1244–1250, 2005     

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.     

Proton conduction promoted by 1H-1,2,3-benzotriazole in non-humidified polymer membranes

Heterocyclic protogenic solvents are promising candidates in production of proton conductive non-humidified membranes. In this work, 1H-1,2,3-Benzotriazole, BTri which is a novel protogenic solvent was incorporated into Nafion and polyvinylphosphonic acid, PVPA to produce novel anhydrous membranes. The composite membranes were characterized using FTIR, TGA and DSC. TGA results confirmed the thermal stability of the membranes and DSC results verified the homogeneity of the materials. The proton conductivity of these polymer electrolyte membranes with respect to BTri content was investigated. 1H-1,2,3-Benzotriazole promoted the proton conductivity of the membranes reaching approximately 10⁻³ S/cm at 150 °C, under anhydrous conditions. Cyclic voltammetry (CV) results demonstrated that 1H-1,2,3-benzotriazole has broad electrochemical stability domain.     

Utilization of poly(ethylene terephthalate) waste for preparing disodium terephthalate and its application in a solid polymer electrolyte

A widespread application and nonbiodegradability of the poly(ethylene terephthalate) (PET) have created a huge amount of waste, which is imposing a serious life-threatening environmental problem. In this study, we have utilized the PET waste to synthesize disodium terephthalate (DST), an organic salt having two Na⁺ ions per molecule. The purity of the DST phase was confirmed by Fourier transform infrared spectroscopy, X-ray diffractometry (XRD), and thermogravimetric analysis (TGA). A new poly(ethylene oxide)–DST polymer electrolyte was synthesized for utilizing Na⁺ ions of the DST. The electrical conductivity of the electrolyte was optimized by varying the [O]/[Na⁺] mole ratio with temperature and the results were explained using the XRD and differential scanning calorimetry studies. The TGA study showed that the electrolyte is thermally stable up to 200 °C. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47612.     

Preparation and application of zinc oxide/poly(m-phenylene isophthalamide) hybrid ultrafiltration membranes

A small molecular-weight cut-off (MWCO) of 6000 Da poly(m-phenylene isophthalamide) (PMIA) embedded zinc oxide (ZnO) hybrid ultrafiltration (UF) membrane was synthesized via nonsolvent-induced phase separation (NIPS). Tests of field emission scanning electron microscope (FE-SEM), energy dispersive X-ray spectroscopy (EDX), atomic force microscopy (AFM), thermal gravimetric analyzer (TGA), Fourier transform infrared (FTIR), capillary flow porometer (CPF), mechanical test, and pure water flux (PWF) for characterization of membranes were carried out. The EDX, FTIR, and TGA indicated the presence of ZnO in the polymer matrix. The hybrid membranes showed enhanced pore density, PWF by the presence of the particles. The contact angle and water flux of modified membrane with 0.03 wt % of nano-ZnO were 47.7° and 52.58 L·m⁻²·h⁻¹ compared to 71.6° and 36.27 L·m⁻²·h⁻¹ respectively; Compared with the hydrophobic membrane, the PMIA membrane, with hydrophilicity, is supposed to exhibit good antifouling properties. Furthermore, the thermal stability and mechanical properties of the modified membranes were increased. Finally, the hybrid membrane was used in treating papermaking white wastewater and exhibited good separation and high water flux. The great properties of the ultrafiltration PMIA membranes indicate their potential for excellent performance in industrial applications. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47583.     

Synthesis and characterization of sulfonated poly(phenylene oxides) as membranes for polymer electrolyte membrane fuel cells

The synthesis of a thermally stable proton conducting polymer based on poly(phenylene oxide) (PPO) was carried out using 2,6‐dimethylphenol (DMP) and 2‐allylphenol (AP) as monomers. The copolymers using the two monomers were prepared with DMP to AP molar ratios of 20:80, 40:60, 60:40, and 80:20. The polymers and the copolymers were blended with poly(vinylidene fluoride) and cast as membranes. All the membranes were sulfonated and characterized for their suitability as a polymer electrolyte membrane. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1792–1798, 2002     

Anhydrous proton conducting polymer electrolytes based on poly(vinylphosphonic acid)-heterocycle composite material

The development of anhydrous proton conducting membrane is important for the operation of polymer electrolyte membrane fuel cell (PEMFC) at intermediate temperature (100-200 °C). In this study, we have investigated the acid-base hybrid materials by mixing of strong phosphonic acid polymer of poly(vinylphosphonic acid) (PVPA) with the high proton-exchange capacity and organic base of heterocycle, such as imidazole (Im), pyrazole (Py), or 1-methylimidazole (MeIm). As a result, PVPA-heterocycle composite material showed the high proton conductivity of approximately 10⁻³ S cm⁻¹ at 150 °C under anhydrous condition. In particular, PVPA-89 mol% Im composite material showed the highest proton conductivity of 7×10⁻³ S cm⁻¹ at 150 °C under anhydrous condition. Additionally, the fuel cell test of PVPA-89 mol% Im composite material using a dry H₂/O₂ showed the power density of approximately 10 mW cm⁻² at 80 °C under anhydrous conditions. These acid-base anhydrous proton conducting materials without the existence of water molecules might be possibly used for a polymer electrolyte membrane at intermediate temperature operations under anhydrous or extremely low humidity conditions.