Nano oxides incorporated sulfonated poly(ether ether ketone) membranes with improved selectivity and stability for vanadium redox flow battery

Three kinds of sulfonated poly(ether ether ketone) (SPEEK)/nano oxide (Al₂O₃, SiO₂, and TiO₂) composite membranes are fabricated for vanadium redox flow battery (VRFB) application. The composite membranes with 5 wt% of Al₂O₃, SiO₂, and TiO₂ (S/A-5 %, S/S-5 %, and S/T-5 %) exhibit excellent cell performance in VRFB. Incorporation of nano oxides (Al₂O₃, SiO₂, and TiO₂) in SPEEK membrane improves in aspect of thermal, mechanical, and chemical stabilities due to the hydrogen bonds’ interaction between SPEEK matrix and nano oxides. The energy efficiencies (EEs) of composite membranes are higher than that of Nafion 117 membrane, owing to the good balance between proton conductivity and vanadium ion permeability. The discharge–capacity retentions of composite membranes also overwhelm that of Nafion 117 membrane after 200 cycles, indicating their good stability in VRFB system. These low-cost SPEEK/nano oxide composite membranes exhibit great potential for the application in VRFB.     

Chemical stability enhancement of crown ether grafted sulfonated poly(arylene ether ketone) fuel cell membrane by cerium ion fixation

In operation of polymer electrolyte membrane fuel cell or direct methanol fuel cell, ·OH radicals are the major cause for the degradation of polymer electrolyte membrane. In order to enhance its antioxidation stability, cerium ion (Ce³⁺, CE), an ·OH radical quencher, is introduced to membrane, as it converts the ·OH radicals into inactive chemicals. In this study, aminoethyl‐15‐crown‐5 (CRE) is grafted on the sulfonated poly(arylene ether ketone) (SPAEK) to prevent the migration of CE ions from the membrane for long‐term antioxidation stability, as CRE forms a coordination complex with CE. The chemical and physical structures of the CRE grafted SPAEK are examined using proton nuclear magnetic resonance, energy dispersive X‐ray, and small‐angle X‐ray scattering spectroscopy. The physical properties of the CRE grafted SPAEK membrane are investigated and compared with those of the CRE blended and CE blended ones. While the grafting of CRE does not significantly affect the thermal and mechanical and water uptake behaviors of membranes, it leads to a significant improvement of antidegradation effect compared with other blend systems according to Fenton's test. The proton conductivity decreases with addition of CE but its effect is lessened by introduction of CRE. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 101–109     

Highly stable side-chain-type cardo poly(aryl ether ketone)s membranes for vanadium flow battery

Vanadium flow batteries(VFBs) have drawn considerable attention as an emerging technology for largescale energy storage systems(ESSs). One of the pivotal challenges is the availability of eligible ion exchange membranes(ICMs) that provide high ion selectivity, proton conductivity, and stability under rigorous condition. Herein, a ‘side-chain-type’ strategy has been employed to fabricate highly stable phenolphthalein-based cardo poly(arylene ether ketone)s(PAEKs) membrane with low area resistance...     

Sulfonated poly(ether ether ketone)/poly(vinylidene fluoride)/graphene composite membrane for a vanadium redox flow battery

Journal of Solid State Electrochemistry - Sulfonated poly(ether ether ketone)/poly(vinylidene fluoride)/graphene (S/P/G) composite membrane was prepared through a solution-casting method for a...     

Controlled sulfonation of poly(arylene ether sulfone)s and poly(arylene ether ketone)s with different molecular structures for polymer electrolyte membranes

Poly(arylene ether sulfone) copolymers derived from 9,9-bis(4-hydroxyphenyl)fluorene, bisphenol S and 4,4′-difluorodiphenylsulfone and poly(arylene ether ketone) copolymers derived from 4-phenoxybiphenyl, diphenyl ether and isophthaloyl chloride were prepared as precursor polymers for sulfonation reaction in which sulfonic groups are introduced quantitatively into specified positions. Sulfonation reaction for these two series of copolymers by concentrated sulfuric acid was successfully carried out to give sulfonated polymers with controlled positions and degree of sulfonation. Thermal stability, moisture absorption and proton conductivity for these two series of copolymers were measured and the results were compared to those of perfluorosulfonic acid polymers.     

Cycling performance and efficiency of sulfonated poly(sulfone) membranes in vanadium redox flow batteries

As an alternative to Nafion® ion exchange membrane, an inexpensive commercially-available Radel® polymer was sulfonated, fabricated into a thin membrane, and evaluated for its performance in a vanadium redox flow battery (VRFB). The sulfonated Radel (S-Radel) membrane showed almost an order of magnitude lower permeability of VO²⁺ ions (2.07 × 10^?7 cm²/min), compared to Nafion 117 (1.29 × 10^?6 cm²/min), resulting in better coulombic efficiency (~ 98% vs. 95% at 50 mA/cm²) and lower capacity loss per cycle. Even though the S-Radel membrane had a slightly higher membrane resistance, the energy efficiency of the VRFB with the S-Radel membrane was comparable to that of Nafion because of its better coulombic efficiency resulting from the lower vanadium ion crossover. The S-Radel membrane exhibited good performance up to 40 cycles, but a decline in performance at later cycles was observed, likely as a result of membrane degradation.     

Synthesis of poly(arylene ether ketone)s bearing skeletal crown ether units for cation exchange membranes

Poly(arylene ether ketone)s (PAEKs) are the most commonly known high‐performance materials used for ion exchange and fuel cell membranes. Described here is the design of novel sulfonated PAEKs (SPAEKs) and nonsulfonated PAEKs containing crown ether units in the main chain, which can be used in sensing applications and ion‐selective membranes. To this end, 4,4′(5′)‐di(hydroxybenzo)‐18‐crown‐6 was synthesized and used as monomer in a step growth polymerization to form crown ether‐containing PAEKs and SPAEKs. The successful synthesis of PAEKs containing 18‐crown‐6 and sulfonate groups was confirmed by gel permeation chromatography, Fourier transform infrared spectroscopy, and nuclear magnetic resonance spectroscopy. Membranes are fabricated from the sulfonated polymers. Potassium ion transport properties of the SPAEK and crown ether‐containing SPAEK membranes are assessed by diffusion dialysis. Potassium ion diffusion in the crown ether‐containing SPAEK membranes is almost four times lower than K⁺ diffusion in the native polymer membranes, without crown ether. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2786–2793     

Polymer blend membranes of sulfonated poly(arylene ether ketone) for direct methanol fuel cell

The blend membranes of sulfonated poly(arylene ether ketone) (sPAEK) (IEC = 1.0 mequiv./g)/Nafion^® and the blend membranes of sPAEK (IEC = 1.0 mequiv./g)/sPAEK (IEC = 1.7 mequiv./g) were prepared. sPAEK with low IEC was introduced to reduce the methanol permeability through the membrane. Morphology, water uptake, proton conductivity and methanol permeability of the blend membranes were investigated by SEM, AFM, AC impedance spectroscopy and permeability measuring instrument. The cross-sections of blend membranes showed phase-separated morphologies. The effect of phase-separated morphology on the properties of blend membranes was investigated. The properties like water uptake, proton conductivity, and methanol permeability of sPAEK/Nafion^® blend membranes showed similar values with sPAEK and properties of sPAEK/sPAEK blend membranes showed intermediate values of two polymers due to the difference in morphology of the blend membranes. sPAEK/sPAEK blend membranes showed relatively high proton conductivity and lowered methanol permeability compared to Nafion^®. sPAEK/sPAEK blend membranes could be a competent substitution for Nafion^®.     

Radiation degradation of poly(arylene ether ketone)s

The resistance of five poly(arylene ether ketone)s with related chemical structures to degradation by ionizing radiation has been studied by ESR spectroscopy and yields of volatile products. All of the polymers showed high resistance to radiation with low yields of radicals after irradiation in vacuum at 77 K (when up to 84% of the radicals were identified as radical anions) and much lower yields at 300 K. The yields of volatile products were much less than reported for poly(arylene sulfone)s [1, 2]. Methyl substitution on a main-chain aromatic ring decreased the radiation resistance, but methane only comprised 10% of the volatile products from the methyl-substituted polymers. A polymer containing an isopropylidene group in the main chain and a substituent aromatic carbonyl showed significantly decreased radiation resistance. Extremely low radical yields were obtained after irradiation in air at 300 K, contrary to many polymers. XPS analysis showed an increase in C–O bonds on the surface after irradiation in air.     

Free volume in glassy poly(arylene ether ketone)s

Amorphous polyarylene ether ketones were examined in the glassy state by positron annihilation lifetime spectroscopy (PALS) and in the melt by standard rheological techniques. Specimens were well-characterized fractions of two isomeric structures. PALS clearly shows that the polymer with meta linkages in its backbone contains larger voids (> 0.25 nm radius). Thus despite their similar bulk densities, the two materials must pack very differently on a local scale. On the other hand, the free volumes inferred from the WLF treatment of melt viscosity data are practically identical in both materials ca. 4% at T_g. The comparison between techniques sheds some light on the distribution of free volume. © 1992 John Wiley & Sons, Inc.     

Synthesis of thermally crosslinkable fluorine‐containing poly(arylene ether ketone)s—II. Propargyl ether terminated poly(arylene ether ketone)s

Novel thermally crosslinkable fluorine‐containing poly(arylene ether ketone)s comprised of 2,3,5, 6‐tetrafluoro‐1,4‐phenylene moiety were synthesized by the termination of polymer chain ends with propargyl ether groups in order to improve solvent resistance. Crosslinking reaction occurred over 250°C through the formation of both chromen ring and polyene structure. This structure change brought about not only the outstanding solvent resistance but also the increase in glass transition temperature (T_g). The cured films also exhibited excellent thermal stability, transparency and hydrophobicity derived from fluorine atoms. Copyright © 2004 John Wiley & Sons, Ltd.     

Proton conductive membranes of sulfonated poly(ether ketone ketone)

Poly(ether ketone ketone) was sulfonated using fumic sulfuric acid and used for preparation of proton conductive membranes. The sulfonation degree was evaluated by elemental and thermal analysis and the IEC values were determined by titration. The proton conductivity of membranes with sulfonation degrees up to 70% was determined as a function of temperature by impedance spectroscopy. Membranes with sulfonation degree 38–70% were tested in DMFC experiments. Their performance was comparable to Nafion^® with the same pretreatment and clearly better than sulfonated poly(ether ether ketone) membranes with similar functionalization. The methanol crossover was lower than that of Nafion^® in the same conditions.     

Ionic conducting membranes based on new sulfonated poly(arylene ether ketone)s for fuel cell applications

The synthesis and characterization of new di‐ and tetra‐sulfonated ether diketone monomers are described. From these monomers, a wide series of sulfonated poly(arylene ether ketone)s (SPAEK) are synthesized by varying the sulfonic acid repartition along the polymer backbones. Their chemical structures are thoroughly characterized by NMR. From these polymers tough membranes are obtained from solution casting method and their water uptake, ionic conductivity, and water/gas permeation properties are determined and compared with those of Nafion membrane. Preliminary fuel cell tests show that SPAEK membranes are promising candidates for fuel cell application. This work brings new insights concerning the beneficial effects of introducing densely sulfonated monomers in a polyarylether macromolecular structure along with fluorinated groups improving conductivity while reducing unwanted excessive swelling. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 771–777     

Synthesis and properties of poly(arylene ether imide ketone)s

Poly(arylene ether ketone)s containing imide units were prepared by the aromatic nucleophilic displacement reaction of the potassium salts of bisphenols with bis(4-fluorobenzoyl)phthalimides in N-methyl-2-pyrrolidone at elevated temperature. The polymers having inherent viscosities of 0.34–0.77 dL/g were obtained in 2 h. The polymers exhibited glass transition temperatures ranging from 216 to 268°C and decomposition temperatures (5% weight loss under air atmosphere) ranging from 450–570°C mainly depending on the bisphenols used in the polymer synthesis. The isothermal TGA measurements (400°C under air or nitrogen atmosphere) revealed that the 4,4'-biphenol- and hydroquinone-based poly(arylene ether ketone imide)s belong to a superior class of heat resistant polymers. The mechanical properties of these polymers are also described. © 1994 John Wiley & Sons, Inc.     

Morphological investigations of block sulfonated poly(arylene ether ketone) copolymers as potential proton exchange membranes

A series of block sulfonated poly(arylene ether ketone) (SPAEK) copolymers with different block lengths and ionic contents were synthesized by a two‐stage process. The morphology of these block SPAEK copolymers was investigated by various methods, such as differential scanning calorimetry (DSC), transmission electron microscope (TEM), and small angle X‐ray scattering (SAXS). Dark colored ionic domains of hundreds of nanometers spreading as a cloud‐like belt were observed in TEM images. The sizes of the ionic domains as a function of block copolymer composition were determined from SAXS curves. The results for the evolution of ionic domains revealed that the block copolymers exhibited more clearly phase‐separated microstructure with increasing ionic contents and hydrophobic sequence lengths. Proton conductivity is closely related to the microstructure, especially the presence of large interconnected ionic domains or ionic channels. Block SPAEK membranes have interconnected ionic clusters to provide continuous hydrophilic channels, resulting in higher proton conductivity. Copyright © 2010 John Wiley & Sons, Ltd.     

Naphthalene‐based poly(arylene ether ketone) copolymers containing sulfobutyl pendant groups for proton exchange membranes

A new monomer 1,5‐bis(4‐fluorobenzoyl)‐2,6‐dimethoxynaphthalene (DMNF) was prepared and further polymerized to form naphthalene‐based poly(arylene ether ketone) copolymers containing methoxy groups (MNPAEKs). The side‐chain‐type sulfonated naphthalene‐based poly(arylene ether ketone) copolymers (SNPAEKs) were obtained by demethylation and sulfobutylation. Flexible and tough membranes with reasonably high mechanical strength were prepared. The SNPAEKs membrane showed anisotropic membrane swelling with larger swelling in thickness than in plane. Transmission electron microscopy (TEM) analysis revealed clear nanophase separated structure of SNPAEKs membranes, which composed of hydrophilic side chain and hydrophobic main‐chain domains. Proton conductivities of copolymers increased gradually with increase in temperature. The highest conductivity of 0.179 S/cm was obtained for SNPAEK‐80 (IEC = 1.82 mequiv/g) at 80 °C, which is higher than that of Nafion117 (0.146 S/cm). The SNPAEKs membranes exhibit the methanol permeability in the range of 3.42 × 10^?8?4.49 × 10^?7 cm²/s, which are much lower than that of Nafion117. They could be the promising materials as alternative to Nafion membrane for direct methanol fuel cells applications. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47:5772–5783, 2009     

Custom-made sulfonated poly (vinylidene fluoride-co-hexafluoropropylene) nanocomposite membranes for vanadium redox flow battery applications

Sulfonated poly (vinylidene fluoride-co-hexafluoropropylene) (SPVDF-co-HFP) based nanocomposite proton exchange membranes (PEM) are fabricated by simple solution casting method using polydopamine coated exfoliated molybdenum disulfide (PDA-MoS₂) nanosheets as an alternative for Nafion® in vanadium redox flow batteries (VRFBs). PDA-MoS₂ is synthesized by the etching of exfoliated MoS₂ nanosheets with dopamine molecule by self-polymerization method. Various characteristic results clearly demonstrated that the incorporated PDA-MoS₂ nanosheets homogeneously distributed into the SPVDF-co-HFP matrix and the presence of NH/NH₂ group electrostatically interacts with SPVDF-co-HFP to form a strong acid-base pair and thus enhances the proton transport via Grotthuss type mechanism. Besides, the improvement in surface hydrophilicity provides the vehicle type conduction also. As a result, SPVDF-co-HFP/PM nanocomposite membranes showed higher proton conductivity in comparison with the pristine membrane. Especially SPVDF-co-HFP/PM-1 membrane demonstrated the excellent proton conductivity of 5.24 × 10⁻³ Scm⁻¹ at 25 °C, lower vanadium-ion permeability of 1.05 × 10⁻⁸ cm²min⁻¹ and highest membrane selectivity of 49.9 × 10⁴ Scm⁻³min. On the other hand, vanadium-ion stability of the membrane increased by adding the PD-MoS₂ content is attributed to their strong electrostatic attraction towards the polymer matrix. Overall results suggested that the SPVDF-co-HFP/PM-1 nanocomposite membrane is found to be a better alternative for commercially costly Nafion in VRFB applications.     

Synthesis and characterization of quaternized poly（phthalazinone ether sulfone ketone） for anion-exchange membrane

Chloromethylated poly(phthalazinone ether sulfone ketone) (CMPPESK) was prepared from poly(phthalazinone ether sulfone ketone) (PPESK) using chloromethyl octyl ethers (CMOE) with lower toxicity as chloromethylated regent.CMPPESK was soluble in N-methyl-2-pyrrolidone (NMP),N,N-dimethylacetamide (DMAc) and chloroform.Quatemized poly(phthalazinone ether sulfone ketone) (QAPPESK) was prepared from CMPPESK by quaternization.QAPPESK had excellent solvent resistance, which was only partly soluble in sulfuric acid (98%) and swollen in N,N-dimethylformamide (DMF).The vanadium redox flow battery (V-RFB) using QAPPESK anion-exchange membrane had better performance with 88.3% of overall energy efficiency.     

Preparation and characterization of poly(ether sulfone)/sulfonated poly(ether ether ketone) blend membranes

Polymer blends of sulfonated poly(ether ether ketone) (SPEEK) and poly(ether sulfone) (PES) in N-methyl-2-pyrrolidinone (NMP) were prepared by solution casting. The investigation on water uptake, methanol uptake, permeability and proton conductivity has been conducted. The spin-lattice relaxation time in the rotating frame of PES/SPEEK blend was obtained from the results of cross-polarization magic angle spinning (CP/MAS) solid state ¹³C NMR. SPEEK blended with PES resulted in increasing , indicating the molecular motion of polymer chain was reduced. The glass transition temperature of the PES/SPEEK blend membranes were predicted by the Kwei equation. PES plays an important role in the decreasing water uptake, methanol uptake and methanol permeability while enhancing the thermal stability of the blend membrane, which shows the feasibility for direct methanol fuel cell.     

Synthesis of copolymers of poly(ether sulfone ether ketone ketone) and poly(ether ketone diphenyl ketone ether ketone ketone) by electrophilic Friedel–Crafts solution polycondensation

A new monomer, 4,4′‐bis(4‐phenoxybenzoyl)diphenyl(BPOBDP), was synthesized via a two‐step synthetic procedure. A series of novel poly(ether sulfone ether ketone ketone)/poly(ether ketone diphenyl ketone ether ketone ketone) copolymers were prepared by electrophilic Friedel–Crafts solution copolycondensation of isophthaloyl chloride (IPC) with a mixture of 4,4′‐diphenoxydiphenylsulfone (DPODPS) and 4,4′‐bis(4‐phenoxybenzoyl)diphenyl (BPOBDP), in the presence of anhydrous aluminum chloride and N‐methylpyrrolidone (NMP) in 1,2‐dichloroethane (DCE). The copolymers with 10–50 mol% DPODPS are semicrystalline and have remarkably increased T_gs over commercially available PEEK and PEKK. The copolymers with 40–50 mol% DPODPS had not only high T_gs of 170–172°C, but also moderate T_ms of 326–333°C, which are extremely suitable for melt processing. These copolymers have tensile strengths of 96.5–108.1 MPa, Young's moduli of 1.98–3.05 GPa, and elongations at break of 13–26% and exhibit excellent thermal stability and good resistance to acidity, alkali, and common organic solvents. Copyright © 2009 John Wiley & Sons, Ltd.