High Ion Exchange Capacity Values Research Articles

Multi-Block Copolymer Membranes Consisting of Sulfonated Poly(p-phenylene) and Naphthalene Containing Poly(arylene Ether Ketone) for Proton Exchange Membrane Water Electrolysis

Glassy hydrocarbon-based membranes are being researched as a replacement for perfluorosulfonic acid (PFSA) membranes in proton exchange membrane water electrolysis (PEMWE). Here, naphthalene containing Poly(arylene Ether Ketone) was introduced into the Poly(p-phenylene)-based multi-block copolymers through Ni(0)-catalyzed coupling reaction to enhance π-π interactions of the naphthalene units. It is discovered that there is an optimum input ratio of the hydrophilic monomer and NBP oligomer for the multi-block copolymers with high ion exchange capacity (IEC) and polymerization yield. With the optimum input ratio, the naphthalene containing copolymer exhibits good hydrogen gas barrier property, chemical stability, and mechanical toughness, even with its high IEC value over 2.4 meq g-1. The membrane shows 3.6 times higher proton selectivity to hydrogen gas than Nafion 212. The PEMWE single cells using the membrane performed better (5.5 A cm-2) than Nafion 212 (4.75 A cm-2) at 1.9 V and 80 °C. These findings suggest that naphthalene containing copolymer membranes are a promising replacement for PFSA membranes in PEMWE.

Structure and properties of sulfonated poly(arylene ether)s with densely sulfonated segments containing mono-, di- and tri-tetraphenylmethane as proton exchange membrane

Multiple factors affecting the sulfonated poly (arylene ether) proton exchange membrane materials are worthy of being systematically explored. In order to investigate the variation of membrane materials based on ion exchange capacity (IEC) and hydrophilic segment length, three series of dense sulfonated poly (arylene ether)s (mt-SPAE-y, dt-SPAE-y and tt-SPAE-y) containing mono-, di- and tri-sulfonated tetraphenylmethane structural units were synthesized. Each series contains three sulfonated copolymers with different IEC values. Small angle X-ray scattering and transmission electron microscopy results show that increasing the IEC value is conducive to the aggregation of hydrophilic ion clusters, while the growth of hydrophilic segment length helps to the formation of larger hydrophilic ion clusters. Both variations favor the construction of connected hydrophilic ion channels. Based on the highest IEC value and the longest hydrophilic segment length, the tt-SPAE-1.94 membrane forms a connected hydrophilic channel that allows it to exhibit the highest proton conductivity and lowest activation energy of the proton conductivity. Good thermal properties, mechanical properties and oxidation resistance lay the foundation for the durability of the membrane in fuel cells. Finally, the tt-SPAE-1.94 membrane was used for membrane electrode assembly at 80 °C and 95% relative humidity, exhibiting a power density of 418 mW cm−2 in H2/air fuel cell test. In summary, both the increase in the IEC value and the length of the hydrophilic segment contribute to the formation of good hydrophilic-hydrophobic phase morphology, thereby enhancing the macroscopic properties of the sulfonated poly (arylene ether) proton exchange membrane material. The results prove that these three series of membranes show outstanding prospects in actual fuel cell operation and have considerable research value.

Surface modification of mesoporous silica by radiation induced graft polymerization of styrene and subsequent sulfonation for ion‐exchange applications

ABSTRACTIn this study, the fabrication of silica‐grafted‐sulfonated styrene (S‐g‐SSt) resin by grafting of styrene onto silanized silica via gamma radiation‐induced polymerization and subsequent sulfonation of the grafted styrene is described. The grafting was strongly affected by the reaction conditions; absorbed dose, monomer concentration, and the type of solvent used. The structural analysis of the silica and all the relevant products were carried out by FTIR, SEM, TGA, XRD, and BET. FTIR analysis confirmed the presence of styrene onto silica and subsequent sulfonation. The BET nitrogen adsorption–desorption isotherms indicated that grafting occurs on the surface as well as inside the pores. Finally, the ion exchange capacity (IEC) of the fabricated S‐g‐SSt was evaluated by ion exchange titrations (back titration method). The IEC was found to be in the range of 0.43–2.97 meq/g depending on the degree of grafting. The facile fabrication method and high IEC value (2.97 meq/g) could lead to potential application of the fabricated S‐g‐SSt resin in ion exchange resin in waste water treatment and metal recovery. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 137, 48835.

(Invited) Poly(norbornene) Hydroxide Conductive Polymers: Stable, High Conductivity Hydroxide Conducting Block Copolymer Membranes and Their Applications

Block copolymer, anion-exchange membranes (AEM) were synthesized using the vinyl-addition polymerization and ring-opening metathesis polymerization of norbornene monomers. The intended use is for use electrochemical devices operating at high pH including fuel cells, electrolyzers, and flow batteries. The focus of this talk is on the impact very high conductivity AEM with low water uptake on device performance. The low molecular weight of the norbornene monomers enabled the design of very high ion exchange capacity (IEC) membranes, up to 4.73 meq/g. A wide variety of norbornene monomers are available allowing for the synthesis of membranes with optimized properties. The norbornene backbone is an all-hydrocarbon structure giving the polymers excellent chemical stability in 1 M NaOH at 80°C. The monomers were synthesized into a multi-block copolymer with hydrophilic and hydrophobic blocks. AEM membranes were solvent cast with and without a supporting polymer reinforcement. The hydrophobic, ion-conducting block of the copolymers formed a lamellar phase during casting. Tetrablock copolymers synthesized by vinyl-addition reaction had an IEC of 1.88 meq/g and conductivity of 123 mS/cm at 80°C. Light cross-linking was found to provide a critical control of water uptake allowing the incorporation of very high IEC without unwanted water uptake. Without light cross-linking, unwanted water uptake would cause swelling and softening of the membrane at high IEC values, as with other AEMs. Thus, the path to achieving exceptionally high ionic conductivity includes high mobility ion channels (achieved here through the use of block copolymers), and light crosslinking to permit the use of high IEC values (e.g. approaching 4 meq/g). The best performing membrane had an ionic conductivity of 212 mS/cm at 80°C. There was little or no drop in ionic conductivity over 1,000 h of aging in 1 M NaOH at 80°C. This is the highest reported hydroxide conductivity at 80°C to date for a chemically stable AEM. The number of bound and free water molecules per ion pair were measured in order to analyze the role of water. The membranes are suitable for electrochemical devices and were used in AEM fuel cells and electrolyzers.

Enhancing hydroxide conductivity of anion exchange membrane via incorporating densely imidazolium functionalized graphene oxide

This study presents a generic method to increase the hydroxide conductivity of anion exchange membranes by tuning the microphase separation structure. Graphene oxide was functionalized with macromolecular brushes for the first time by a precipitation polymerization method. Densely-functionalized imidazolium groups were aligned in the configuration of macromolecular brushes to act as hydroxide-conductive groups, which endow the functionalized graphene oxide with a high ion exchange capacity value of 3.05 mmol g−1. Polymer-inorganic composite membrane for anion exchange membrane fuel cell was fabricated by incorporating the imidazolium-functionalized graphene oxide into imidazolium-functionalized bisphenol A-type polysulfone. The dense imidazolium groups manipulated the aggregation of conductive groups at the polymer/filler interfaces to induce the well-defined microphase structure of composite membranes, constructing low-resistance channels for ionic transport. The activation energy of hydroxide transport in composite membranes was reduced to 25.17–13.62 kJ mol−1, in comparison with 28.63 kJ mol−1 for control membrane. The hydroxide conductivity of composite membrane was elevated to 22.02 mS cm−1 at 30 °C, which is 2.10 times of that for control membrane. The maximum power density of single fuel cell of 78.7 mW cm−2 at 60 °C was thus achieved.

Development of Highly Conductive and Highly Durable All-Aromatic Anion Exchange Membranes By Using Thermally Convertible Precursor Polymer

Solid Alkaline Fuel Cells (SAFCs) using Anion Exchange Membranes (AEMs) attracts increasing attention for next-generation fuel cell technology. SAFCs have many advantages over proton exchange membrane fuel cell such as variable choice of metal electrode catalyst and fuels. However, the commercialization of SAFCs is limited due to the lack of high-performance AEMs. Commonly, AEMs have low ionic conductivity and poor durability in alkaline medium. In this study, we developed a novel AEM comprises of wholly aromatic, anthracene-based, backbone as a chemically durable membrane. Commonly, such kind of polymers exhibits very low solubility in common organic solvent due toπ-πstacking. Thus the processability into a membrane is very difficult. Our unique molecular design is employing bulky Thermal Leaving Group (TLG) on the precursor polymer allowing this polymer to be cast as a film due to high solubility (>300 mg/ml). Then, TLG on the membrane film was removed by performing retro Diels-Alder reaction1,2 in the solid state to obtain a wholly aromatic membrane (figure 1 (a)). The precursor polymer was obtained by Suzuki-Miyaura coupling of the monomers. The methyl group of the resulting polymer was converted to benzyl bromide and finally to quaternary trimethylammonium bromide to afford the target precursor polymer (TPP). The polymer structure and molecular weight were analyzed by 1H-NMR and GPC. Ion exchange capacity (IEC) was determined by titration. The in-plane ionic conductivity of the membrane is evaluated by AC impedance method. Stability test in hot alkaline solution and Fenton solution was performed to check the chemical durability of the membrane. Molecular weight and IEC of synthesized TPP are 13,000 g/mol and IEC 2.49, respectively. Target polymer (TP) membrane was then obtained by just heating TPP membrane and removing TLG. The best heating temperature was determined to be 180 oC by TGA-MS analysis. IEC of the membrane has increased to 3.16 after thermal conversion. Despite higher IEC value, water uptake of TP membrane was lower than TPP membrane probably due to the strong intermolecular interaction of TP membrane. Therefore, TP membrane keeps higher IEC even after water uptake and this may result in high anion conductivity. Figure 1 (b) shows the ionic conductivity of TP membrane before and after the durability test. The membrane kept initial HCO3 - conductivity even after exposed to a very harsh alkaline solution (8M NaOH for 21 days at 80 oC) and Fenton solution (H2O2 3 wt%, FeSO4 3 ppm at 60 oC for 8 hours). This is a solid proof that the TP membrane has both high durability and high conductivity, meeting for SAFC application. These findings suggest that the use of TLG on polymer backbone allow development of new design concepts for highly-durable and highly conductive AEMs.

Sulfonated Terpolymers Containing Alkylene and Perfluoroalkylene Groups: Effect of Aliphatic Groups on Membrane Properties and Interface with the Catalyst Layers

Two series of terpolymers (SPA-A, -B, and -C) composed of perfluoroalkylene, alkylene, and sulfonated phenylene (SP) groups were prepared to investigate the effect of aliphatic groups and their compositions onto the membrane properties for proton exchange membrane fuel cells. The composition of perfluoroalkylene (m) and alkylene groups (n) in SPA terpolymers was controlled to be m/n = 0.5/0.5 for SPA-A, 0.65/0.35 for SPA-B, and 1/0 for SPA-C. SPA terpolymers provided thin and bendable membranes with ion exchange capacity (IEC) ranging from 1.61 to 3.18 mequiv g–1. Introducing alkylene groups into the polymer main chain was effective in achieving high IEC values. SPA-B membranes with lower alkylene group content showed slightly more developed phase-separated morphology than that of SPA-A membranes with higher alkylene group content. The developed phase separation with interconnected ionic channels resulted in high proton conductivity for SPA-B membranes. The alkylene groups in the main chain also contributed to improving mechanical properties as suggested by stress versus strain curves, in which SPA membranes exhibited higher Young’s moduli and higher yield strength than those of copolymer (SPA-C) membranes with no alkylene groups. An H2/O2 (or air) fuel cell with SPA-B membrane exhibited high open circuit voltage (OCV, 0.99 V at 100% RH with O2), low ohmic resistance (0.05 Ω cm2 at 100% RH with O2), and good current/voltage performance, reflecting the properties of SPA-B membrane. However, interfacial compatibility with the catalyst layers was somewhat deteriorated with SPA-B membrane to cause lower mass activity (70 A g–1 at 100% RH) of the cathode compared to that with SPAF membrane (102 A g–1 at 100% RH). SPA-B membrane was durable in OCV hold test for 1000 h with slight degradation in alkylene groups.

Poly(ether ether ketone) grafted with sulfoalkylamine as proton exchange membrane

A series of side-chain-type sulfonated poly(arylene ether ketone)s with high ion exchange capacity (IEC) values were prepared by polycondensation reaction of 4,4′-difluorobenzophenone with 2,2′-bis(3-amino-4-hydroxyphenyl) and bisphenol A, followed by post-grafting reaction using 1,4-butanesultone. For these obtained membranes, sulfoalkylamine functionalized poly(ether ether ketone) (SAm-PEEK)-0.8 with the highest IEC of 3.42 mequiv. g−1 displayed the highest proton conductivity of 0.11 S cm−1 at 25°C and 0.167 S cm−1 at 60°C, respectively. The morphology of these membranes was investigated by transmission electron microscope analysis. The result showed that these membranes exhibited well-connected hydrophilic channels due to their high IEC values and densely populated flexible acid side chains. Owing to their low methanol permeability and high selectivity, SAm-PEEK- x membranes are promising candidates for direct methanol fuel cell applications.

Novel anion exchange membranes based on quaternized diblock copolystyrene containing a fluorinated hydrophobic block

With the aim to enhance the hydrophilic–hydrophobic separation and thus improve the anion conductivity of diblock copolymer anion exchange membranes (AEMs), a fluorinated hydrophobic block was introduced into quaternized diblock copolystyrene. Two fluoro-containing monomers (i.e., 4-fluorostyrene (4FS) and 2, 3, 4, 5, 6-pentafluorostyrene (PFS)) were polymerized into a poly(4-vinyl benzyl chloride)-based macroinitiator (Macro-PVBC263) via reversible addition–fragmentation chain transfer (RAFT) polymerization. This route led to the corresponding diblock copolymers PVBC263-b-P4FSy and PVBC263-b-PPFSy, which served to prepare AEMs (i.e., PVBC263-b-PPFSy-OH and PVBC263-b-P4FSy-OH, respectively) via quaternization with trimethyl amine (TMA) and subsequent ion-exchange. As expected, the as-obtained AEMs showed well-defined lamellar morphologies, as revealed by small-angle X-ray scattering (SAXS) and atomic force microscopy (AFM). Consequently, all the fluorinated diblock copolymer-based AEMs showed high anion conductivities. PVBC140-b-P4FS38-OH showed the highest hydroxide conductivity (86.1 mS/cm) with an ion exchange capacity (IEC) of 4.27 meq/g. Interestingly, despite its high IEC, PVBC263-b-P4FS38-OH showed a reasonable water uptake (WU) of 37.5% as a result of the presence of hydrophobic fluorinated block segments. Thus, proper ion conducting channels are believed to be built by facilitating hydrophilic–hydrophobic phase separation processes driven by the fluoro-substituted functionalities. Despite their high IEC values in terms of hydrophobicity, the WU and swelling ratio of the AEMs prepared herein did not increase significantly, especially at elevated temperatures. All the AEMs preserved over 86% of their initial hydroxide conductivity after 20 d of alkaline stability testing (1 M aqueous NaOH) at 80 °C.

Synthesis and Morphology Study of SEBS Triblock Copolymers Functionalized with Sulfonate and Phosphonate Groups for Proton Exchange Membrane Fuel Cells

Aromatic rings of poly(styrene-b-(ethylene-r-butylene)-b-styrene) triblock copolymer (SEBS) were functionalized with various acid functional groups for proton exchange membrane (PEM) applications. Three different acid functional groups (fluoroalkylsulfonic acid, arylsulfonic acid, and arylphosphonic acid) were introduced into SEBS via borylation of aromatic C–H bonds and Suzuki coupling reactions. The incorporation of acid side groups selectively into the polystyrene block of SEBS created nanometer-scale phase separated morphology composed of hydrophilic and hydrophobic domains in which the morphology structures and interdomanin distances are dependent on the chemical structure of acid side chains. Despite high ion exchange capacity value, the aryl phosphonated polymer (SEBS-P) showed the lowest water uptake and significantly lower proton conductivity compared to sulfonated SEBS PEMs because of the low acidity of phosphonic acid. Compared to aryl sulfonated SEBS-S2, fluoroalkyl sulfonated SEBS-S1 showed better proton conductivity at low relative humidity condition (<50%), which is ascribed to the stronger acidity and more compact ionic domains. Morphology study of SEBS-S1 indicates that due to both hydrophobic and oleophilic nature of fluoroalkyl chains, fluoroalkyl sulfonate chains of SEBS-S1 induced more dense ionic self-aggregation.

Preparation and performance evaluation of novel alkaline stable anion exchange membranes

Abstract Novel alkaline stable anion exchange membranes are prepared from various amounts of N-methyl dipicolylamine (MDPA) and brominated poly (2,6-dimethyl-1,4-phenylene oxide) (BPPO). The dipicolylamine and MDPA are synthesized through condensation reaction and confirmed by 1 H NMR spectroscopy. The morphologies of prepared membranes are investigated by atomic force microscopy (AFM), fourier transform infrared spectroscopy (FTIR), 1 H NMR spectroscopy and scanning electron microscopy (SEM). The electrochemical and physical properties of AEMs are tested comprising water uptake (WU), ion exchange capacity (IEC), alkaline stability, linear expansion ratio (LER), thermal stability and mechanical stability. The obtained hydroxide conductivity of MDPA-4 is 66.5 mS/cm at 80 °C. The MDPA-4 membrane shows good alkaline stability, high hydroxide conductivity, low methanol permeability (3.43 × 10 −7 cm 2 /s), higher selectivity (8.26 × 10 7 mS s/cm 3 ), less water uptake (41.1%) and lower linear expansion (11.1%) despite of high IEC value (1.62 mmol/g). The results prove that MDPA membranes have great potential application in anion exchange membrane fuel cell.

Anion Conductive Aromatic Copolymers from Dimethylaminomethylated Monomers: Synthesis, Properties, and Applications in Alkaline Fuel Cells

A novel series of anion conductive aromatic copolymers were synthesized from preaminated monomers (2,5-, 3,5-, or 2,4-dichloro-N,N-dimethylbenzylamine), and their properties were investigated for alkaline fuel cell applications. The targeted copolymers (QPE-bl-11a, -11b, and -11c) were synthesized via nickel-mediated Ullmann coupling polymerization, followed by quaternization and ion exchange reactions. Unlike the conventional method involving chloromethylation or bromination, this method provided copolymers with well-defined chemical structure. The hydrophilic components of the copolymers were composed of chemically stable phenylene main chain modified with high-density ammonium groups. Oligo(arylene ether sulfone ketone)s were employed as a hydrophobic block. QPE-bl-11a gave tough and bendable membranes by solution casting. The obtained membrane with the highest ion exchange capacity value (IEC = 2.47 mequiv g–1) showed high hydroxide ion conductivity (130 mS cm–1) in water at 80 °C. The QPE-bl-11a memb...

An effective strategy to increase hydroxide-ion conductivity through microphase separation induced by hydrophobic-side chains

A highly conductive and durable anion exchange membrane (AEM) is an essential component for alkaline electrochemical conversion and storage systems. Contrary to the conventional wisdom that the ionic conductivity can be improved by increasing the ion exchange capacity (IEC) through a cross-linking process, in this work, a new approach to improve the ionic conductivity by enhancing the ionic mobility is adopted. The microstructure of quaternary ammonia poly (2, 6-dimethyl-1, 4-phenylene oxide) (QAPPO) is manipulated through grafting with hydrophobic side chains, which will drive the well-established hydrophilic/hydrophobic domains and nano-phase separated, well-connected ionic channels. As a result, the local hydroxide concentration is enhanced by the novel microstructure, thereby improving the ionic conductivity of the as-prepared ionomers. The as-prepared ionomers, denoted as self-aggregated QAPPO-CF, with an intermediate IEC value achieved an ionic conductivity of 65 mS cm−1 at 80 °C, outperforming the QAPPO with an even higher IEC value. This result suggests that the microphase separation is an effective approach to enhance the ionic conductivity.

Ladder-type aromatic block copolymers containing sulfonated triphenylphosphine oxide moieties as proton conductive membranes

The synthesis and characterization of ladder-type aromatic block copolymers containing sulfonated triphenylphosphine oxide moieties (LadP-SPE) are reported. Through aromatic nucleophilic substitution polycondensation and Pd-catalyzed intrapolymer Heck reaction, the target copolymers LadP-SPE with high molecular weight (Mn = 47–50 kDa, Mw = 289–579 kDa) and different ion exchange capacity (IEC) values (1.04, 1.84 and 2.22 meq g−1, by titration) were prepared. By solution casting method, all the copolymers gave transparent and bendable membranes. The membrane with IEC = 2.22 meq g−1 exhibited high proton conductivity in wide range of relative humidity (RH) at 80 °C (ca. 1.6 mS cm−1 at 20% RH and 351.2 mS cm−1 at 95% RH). Moreover, the stiff ladder structure strengthened the molecular chain which contributed to the membrane with high IEC value and water uptake to have desirable mechanical stability up to 90% RH at 80 °C.

Novel Nano-Zirconium Antimonate as Cation Exchange Material for Organic Dye Pollutants Purification

Nano-zirconium antimonate was successfully prepared using two different techniques of sol-gel and homogeneous precipitation. The different preparation parameters affecting onto the two preparation techniques such as HCl concentration, reactants molar ratio and effect reaction temperature were optimized to attain cation exchange material with high ion exchange capacity and produced in nano-size structure. The different prepared samples were screened based on their ion exchange capacities. The most proper prepared sample produced from the sol-gel technique poses higher ion exchange capacity value of 3.5meq/g compared with that produced from the homogeneous precipitation that recorded ion exchange capacity of 2.8meq/g. The physico-chemical properties of the two nano-zirconium antimonate samples produced from each technique were compared using various analytical techniques such as XRD, SEM and TEM. XRD results indicated that the sample produced from the homogeneous precipitation attains high crystallinity degree compared with the amorphous sol-gel prepared sample. The morphological structure investigation evident the nano-spherical morphology for the two prepared samples. The average nano-size of the homogeneous precipitation sample of 22nm is smaller than that of the sol-gel sample that recorded 34nm. The dye decontamination behavior of the two prepared nano-zirconium antimonate samples was compared for C.I basic blue 3dye. The sol-gel prepared sample recorded higher dye decolorization of 81.5% compared with 54% for the homogeneous precipitation sample.

Novel nanostructured semicrystalline ionomers by chemoselective sulfonation of multiblock copolymers of syndiotactic polystyrene with polybutadiene

Novel semi-crystalline sulfonated copolymers (sPS(B-SA)) have been synthesized by sulfonation of multiblock copolymers of syndiotactic polystyrene with cis-1,4-polybutadiene (sPSB), using a two-stage solution process comprising the addition of thiolacetic acid to the butadiene units, followed by the in situ oxidation of the thioacetyl moieties with performic acid. The sulfonation process is quantitative, chemoselective, cheap and more environmentally benign than similar methods previously reported; in addition it allows achieving high ion exchange capacity values (up to 4.48 equiv. per kg). The sPS(B-SA)s are crystalline, preserving the native polymorphic behavior of the crystalline syndiotactic polystyrene segments. Thin films of sPS(B-SA) samples show a phase separated morphology at the nanometer scale evidenced by tapping mode and tunneling current atomic force microscopy; proton conductive regions embedded in a hard-hydrophobic matrix of syndiotactic polystyrene were actually observed.

Synthesis and characterization of sulfonated block copolyimides derived from 4,4'‐sulfide‐bis(naphthalic anhydride) for proton exchange membranes

ABSTRACTA series of sulfonated copolyimides (SPIs) with hydrophilic segment length of 20–60 based on 4,4′‐sulfide‐bis(naphthalic anhydride) (SBNA) have been successfully synthesized to improve hydrolytic stability and proton conductivity. The SPI membranes were cast from their m‐cresol solutions, and they were characterized by determining the water uptake, water swelling ratio, mechanical properties, hydrolytic stability, oxidative stability, and proton conductivity. It was found that the water uptake of SPI membranes was low and decreased as the hydrophilic segment length increased, which led to good dimensional stability. In addition, the SPI membranes with low ion‐exchange capacity (IEC) value displayed excellent hydrolytic stability and retained good mechanical properties even after harsh hydrolysis testing, in which the block SPI with hydrophilic segment length of 40 had the best hydrolytic stability, while those with high IEC value showed an apparent decrease. All of the block SPI membranes show better conductivity than the random ones at the temperature range from 30 to 70°C. Interestingly, the proton conductivities of random SPI membranes were higher than that of corresponding block ones at 90°C. The block SPI with hydrophilic segment length of 40 gave the highest proton conductivity as the temperature increased among the block SPIs. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41501.

Properties of phosphoric acid doped Poly(benzimidazole/sulfone/siloxane/amide)/Sulfonated Polystyrene/Silica nanoparticle-based proton exchange membranes for fuel cells

New siloxane and sulfone containing poly(benzimidazole/sulfone/siloxane/amide) (PBSSA) has been prepared for the formation of hybrid membranes (PBSSA/PS-S/SiNPs) with sulfonated polystyrene (PS-S) and 0.1 wt%-2 wt% silica nanoparticles (SiNPs). Field emission scanning electron micrographs showed good dispersion of filler, formation of dense nanoporous honeycomb like structure and uniform ionic pathway in these hybrids. The porous membrane structure was responsible for the fine water retention capability and higher proton conductivity of the new hybrids. Increasing the amount of nanoparticles from 0.1 wt% to 2 wt% increased the tensile stress of acid doped PBSSA/PS-S/SiNPs nanocomposites from 65.7 MPa to 68.5 MPa. A relationship between nanofiller loading and thermal stability of the membranes was also experientially studied, as the glass transition temperature of phosphoric acid doped PBSSA/PS-S/SiNPs nanocomposites increased from 207 °C to 215 °C. The membranes also had higher ion exchange capacity (IEC) around 2.01 mmol/g to 3.01 mmol/g. The novel membranes with high IEC value achieved high proton conductivity of 1.10–2.34 S/cm in a wide range of humidity values at 80 °C which was higher than that of perfluorinated Nafion®117 membrane (1.1 × 10−1 S/cm) at 80 °C (94% RH). A H2/O2 fuel cell using the PBSSA/PS-S/SiNP 2 (IEC 3.01 mmol/g) showed better performance than that of Nafion® 117 at 40 °C and 30% RH.

Fuel cell membranes of phosphoric acid–doped poly(benzimidazole/ether/siloxane/amide)/sulfonated polystyrene/silica nanoparticle nanocomposites

Poly(benzimidazole/ether/siloxane/amide) (PBESA) having siloxane and ether groups in the backbone has been prepared using 4-(3,4-diaminophenoxy)benzene-1,2-diamine, bis(carboxypropy)tetramethyldisiloxane, and 4,4′-oxydianiline via polyphosphoric acid processes with heating up to 160°C. The sulfonation of polystyrene (PS-S) was conducted using 98% sulfuric acid. Afterward, a series of hybrid membranes using PBESA/PS-S/silica nanoparticles (SiNPs) have been developed with 0.1–2 wt% nanofiller. Later, the membranes were doped with phosphoric acid and subjected to various characterization techniques. Field emission scanning electron micrographs (FESEMs) showed gyroid-like patterning of nanoporous membranes with uniform ionic pathways. Fine water retention capability and higher proton conductivity of new hybrids, owing to consistent porous membrane structure, were observed. Increasing the amount of nanoparticles (0.1–2 wt%) also enhanced the tensile stress of acid-doped PBESA/PS-S/SiNPs nanocomposites from 64.9 to 68.1 MPa. There existed a relationship between nanofiller loading and thermal stability of the membranes. The glass transition temperature of phosphoric acid–doped PBESA/PS-S/SiNPs nanocomposites increased from 202 to 214°C. The membranes also had fine ion exchange capacity (IEC) of around 2.5–3.7 mmol g−1. Novel membranes with high IEC value achieved high proton conductivity of 1.26–2.74 S cm−1 in a wide range of humidity values at 80°C, which was higher than that for perfluorinated Nafion® 117 membrane (1.1 × 10−1 S cm−1 at 80°C, 94% relative humidity (RH)). The fuel cell (hydrogen/oxygen) using PBESA/PS-S/SiNPs 2 (IEC 3.7 mmol g−1) showed better performance than that of Nafion® 117 at 40°C (30% RH).

Fuel cell membranes prepared from multi-walled carbon nanotubes and silica nanotubes-filled sulfonated polyamide/sulfonated polystyrene porous blend films

A sulfonated polyamide (PA-S) was first synthesized through polycondensation of sulfonated 4,4′-oxydianiline and terephthaloyl chloride. The sulfonation of polystyrene (PS-S) was conducted using a mild sulfonating reagent (98% H2SO4). Two categories of mechanically robust and thermally stable nanocomposites, based on multi-walled carbon nanotube (MWCNT) and silica nanotube (SiNT), i.e. PS-S/PA-S/MWCNT and PS-S/PA-S/SiNT, were prepared by solution blending. Scanning electron micrographs showed good dispersion of filler and adhesion of matrix on the surface of nanotube. Accordingly, a symmetric membrane structure with dense porous top layer, porous sublayer, and fully developed micropores at the bottom were observed. The porous membrane structure was accountable for the excellent water retention capability, and so, higher proton conductivity of new hybrids. Increasing the amount of nanotube from 0.5 to 2 wt.% increased the ultimate tensile stress of functional PS-S/PA-S/MWCNT nanocomposites 51.8–62.2 MPa compared with non-functional filler (33.4 MPa) and PS-S/PA-S/SiNT. A rapport between nanotube loading and thermal stability of the materials was also observed as the glass transition in PS-S/PA-S/MWCNT nanocomposites increased from 202 to 206℃. MWCNT-based blend membranes had higher ion exchange capacity (IEC), around 2.99–3.42 mmol/g. Novel membranes with high IEC value achieved high proton conductivity of 1.28–2.23 S/cm in a wide range of humidity values at 80℃ which was higher than that of perfluorinated Nafion®117 membrane (1.1 × 10−1 S/cm) at 80℃ (94% relative humidity; RH) which was used as benchmark. Moreover, a H2/O2 fuel cell using the PS-S/PA-S/MWCNT (IEC 3.42 mmol/g) also showed better performance than that of Nafion®117 at 40℃ and 30% RH.