Synthesis of Proton Exchange Membranes with Pendent Phosphonic Acid Groups by Irradiation Grafting of VBC

Proton exchange membranes with pendent phosphonic acid groups were synthesized by pre‐irradiation grafting from vinylbenzyl chloride onto FEP and ETFE films with subsequent Arbuzov phosphonation. Free phosphonic acid groups, which are necessary for proton conductivity, were obtained by acid ester hydrolysis. The phosphonated membranes were characterized by phosphonation degree, FTIR‐spectroscopy, ion exchange capacity (IEC), oxidation stability, swelling properties, and thermal properties (TGA).     

Comparative study on the preparation and properties of radiation‐grafted polymer electrolyte membranes based on fluoropolymer films

In this study the fluoropolymers, poly(ethylene‐co‐tetrafluoroethylene) (ETFE) and poly(vinylidene fluoride) (PVDF) films, together with the radiation‐induced crosslinked polytetrafluoroethylene (cPTFE) film were compared on the basis of their preparation and properties of radiation‐grafted polymer electrolyte membranes. The polymer electrolyte membranes were prepared by radiation grafting of styrene into the base films and subsequent sulfonation. The proton conductivity and chemical stability of the three types of membranes with a similar ion exchange capacity (IEC) near 1.0 mmol/g were investigated and are discussed in detail. Although the ETFE‐based polymer electrolyte membrane was relatively more stable, its proton conductivity was lower than those of the PVDF‐ and cPTFE‐based membranes. On the other hand, the cPTFE‐based membrane showed a significantly higher proton conductivity, but its chemical stability was shorter than that of the ETFE‐based membrane. It is considered that the difference in the preparation and properties of the polymer electrolyte membranes was due to the difference in the degree of crystallinity as well as in the chemical structure of the fluoropolymer base films. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1966–1972, 2007     

Novel fluorinated polymers bearing phosphonated side chains: synthesis, characterization and properties

A new class of aryl trifluorovinyl ether monomers containing phosphonated oligo(ethylene oxide) units were designed and synthesized. Novel fluorinated polymers containing perfluorocyclobutane and phosphonic acid moieties were prepared from these monomers via the thermal cyclopolymerization and hydrolysis reaction. The structures of these monomers and polymers were characterized by nuclear magnetic resonance spectroscopy and fourier transform spectroscopy. The thermal properties of these polymers were evaluated with differential scanning calorimetry and thermo-gravimetric analysis. The 5% weight loss of these polymers was in range of 258–270 °C in nitrogen, but no glass transition temperatures were detected. The polymers showed good solubility in organic solvents such as dimethyl sulfoxide and N,N-dimethylacetamide. In addition, the basic membrane properties of the membranes such as water uptake and proton conductivity were also measured at room temperature. The membranes exhibited high water uptake (up to 44.7%) due to the high level of phosphonation content. The proton conductivities of the membranes under 100% relative humidity were in the range of 0.032–0.068 S/cm, which entitled them as candidates for proton exchange membranes.     

Sulfonated graphene oxide‐doped proton conductive membranes based on polymer blends of highly sulfonated poly(ether ether ketone) and sulfonated polybenzimidazole

Simultaneously improving the proton conductivity and mechanical properties of a polymer electrolyte membrane is a considerable challenge in commercializing proton exchange membrane fuel cells. In response, we prepared a new series of miscible polymer blends and thus the corresponding crosslinked membranes based on highly sulfonated poly(ether ether ketone) and sulfonated polybenzimidazole. The blended membranes showed more compact structures, due to the acid‐base interactions between the two constituents, and improved mechanical and morphological properties. Further efforts by doping sulfonated graphene oxide (s‐GO) forming composite membranes led to not only significantly elevated proton conductivity and electrochemical performance, but also better mechanical properties. Notably, the composite membrane with the filler content of 15 wt % exhibited a proton conductivity of 0.217 S cm^?1 at 80 °C, and its maximum power density tested by the H₂/air single PEMFC cell at room temperature reached 171 mW cm^?2, almost two and half folds compared with that of the native membrane. As a result, these polymeric membranes provided new options as proton exchange membranes for fuel‐cell applications. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46547.     

Comparative study of composite membranes from nano‐metal‐oxide‐incorporated polymer electrolytes for direct methanol alkaline membrane fuel cells

A series of six composite membranes was prepared with two polymer electrolytes and three inorganic fillers, namely, silica, titania, and zirconia by a solution casting method. Two polymer electrolytes, that is, anion‐exchange membranes, were prepared from polystyrene‐block‐poly(ethylene‐ran‐butylene)‐block‐polystyrene (PSEBS) and polysulfone by chloromethylation and quaternization. A preliminary characterization of the ionic conductivity, methanol permeability, and selectivity ratio was done for all of the prepared composite membranes to check their suitability to work in direct methanol alkaline membrane fuel cells (DMAMFCs). The DMAMFC performance was analyzed with an in‐house fabricated single cell unit with a 25‐cm² area. Maximum performance was achieved for the composite membrane quaternized PSEBS/7.5% TiO₂ and was 74.5 mW/cm² at 60°C. For the comparison purposes, a commercially available anion‐exchange membrane (Anion Membrane International‐7001) was also investigated throughout the study. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Synthesis and characterization of polybenzimidazole/α‐zirconium phosphate composites as proton exchange membrane

To improve the high‐temperature performance of proton exchange membranes, the polybenzimidazole (PBI)/α‐zirconium phosphate (α‐Zr(HPO₄)₂·nH₂O, α‐ZrP) proton exchange composite membranes were prepared in this study. PBI polymer containing a large amount of ether units has been synthesized from 3,3′‐ diaminobenzidine (DAB) and 4,4′‐oxybis (benzoic acid) by a direct polycondensation in polyphosphoric acid. The polymer exhibited a good solubility in most polar solvents. Inorganic proton conductor α‐ZrP nanoparticles have been obtained using a synthesis route involving separate nucleation and aging steps (SNAS). The effects of α‐ZrP doping content on the composite membrane performance were investigated. It was found that the introduction of ZrP improved the thermal stability of the composite membranes. The PBI/ZrP composite membranes exhibited excellent mechanical strength. The composite membrane with 10 wt% ZrP showed the highest proton conductivity of 0.192 S cm^?1 at 160°C under anhydrous condition. The proton conducting mechanism of the PBI/ZrP composite membranes was proposed to explain the proton transport phenomena. The experimental results suggested that the PBI/ZrP composite membranes may be a promising polymer electrolyte used in high temperature proton exchange membrane fuel cells (HT‐PEMFCs) under anhydrous condition. POLYM. ENG. SCI., 56:622–628, 2016. © 2016 Society of Plastics Engineers     

Phosphonic acid-containing homo-, AB and BAB block copolymers via ATRP designed for fuel cell applications

The synthesis of various block copolymers containing phosphonic acid moieties is described. Poly(styrene)/PDEVBP AB block copolymers were obtained by atom transfer radical polymerization (ATRP) of diethyl p-vinylbenzyl phosphonate (PDEVBP). Subsequently, BAB block copolymers with tailored architecture composed of the phosphonated monomer and poly(ether ether ketone) were obtained by a combination of polycondensation chemistry and ATRP. The quantitative deprotection of the ethyl phosphonates led to the corresponding free phosphonic acids, which can be applied as polymer electrolyte membranes for fuel cells. In addition, all materials showed high thermal stability. The proton conductivity properties of the ionomers were investigated. The phosphonic acid-containing (co)polymers exhibited a linear increase of the conductivity with the temperature with a maximum value of 4.5 × 10⁻⁴ S/cm in anhydrous conditions.     

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.     

Electrochemical characterization of radiation-grafted ion-exchange membranes based on different matrix polymers

Seven proton conducting membranes based on different commercial fluoropolymer films were prepared by radiation grafting with styrene followed by sulfonation. These membranes were studied as candidates for fuel cell electrolyte membranes and compared to Nafion^® 105 and 117 with respect to conductivity, oxygen and hydrogen permeability, kinetics of the oxygen reduction reaction (ORR) and performance in a fuel cell. The dependence of the conductivity of the membranes on the relative humidity (RH) and temperature was also determined. The conductivity was observed to depend on the membrane thickness and the water uptake. The dependence of the conductivity on the temperature and the RH was the same for all of the experimental membranes. Reactant gas permeabilities appeared to depend only slightly on the matrix material and no major differences in the Tafel slopes and exchange current densities of the ORR were observed. Membranes with high water uptakes appeared to be less durable in the fuel cell than membranes with low water uptakes. Thus to prepare a membrane that is durable under the fuel cell conditions, the water uptake must remain low even at the expense of the conductivity.     

Proton exchange composite membranes from blends of brominated and sulfonated poly(2,6‐dimethyl‐1,4‐phenylene oxide)

New composite proton exchange membrane was prepared by mixing a 1‐methyl‐2‐pyrrolidone (NMP) solution of sulfonated poly(2,6‐dimethyl‐1,4‐phenylene oxide) (SPPO) in sodium form and brominated poly(2,6‐dimethyl‐1,4‐phenylene oxide) (BPPO) for hydrophilic‐hydrophobic balance, then casting the solution as a thin film, evaporating the solvent, and treating the membrane with aqueous hydrochloric acid. The resulting membranes were subsequently characterized using FTIR‐ATR, SEM‐EDXA, and TGA instrumentation as well as measurements of basic properties such as ion exchange capacity (IEC), water uptake, proton conductivity, methanol permeability, and single cell performance. Water uptake, IEC, proton conductivity, and methanol permeability all increased with a corresponding increase of SPPO content. By properly compromising the conductivity and methanol permeability, membranes with 60–80 wt % SPPO content exhibited comparable proton conductivity to that of Nafion^® 117, with only half the methanol permeability, thereby demonstrating higher single cell performance. The membranes developed in this study could thus be a suitable candidate electrolyte for proton exchange membrane fuel cells (PEMFCs). © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Preparation of phosphorylated nata‐de‐coco for polymer electrolyte membrane applications

Fuel cells are being developed to overcome the global energy crisis. The objective of this research is to prepare an environmental‐friendly and cheap material as the polymer electrolyte membrane. Coconut water was fermented by Acetobacter xylinum to produce nata‐de‐coco and the phosphorylation was carried out by microwave‐assisted reaction. The resulting membranes are characterized by ion exchange capacity, contact angle, proton conductivity, swelling index, methanol permeability, mechanical properties measurement and morphological analysis. At the optimum phosphorylation condition using 17.35 mmol of phosphoric acid, membrane showed a proton conductivity of 1.2 × 10^?2 S/cm and a methanol permeability of 2.3 × 10^?6 cm²/s. The tensile strength of the produced membranes increases significantly and the arrangement of the cellulosic fibers are kept well‐aligned. It is concluded that a green and sustainable natural resources can be used for preparing electrolyte membrane. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Proton Conducting Sulphonated Fluorinated Poly(Styrene) Crosslinked Electrolyte Membranes

Potential membranes for polymer electrolyte membrane fuel cell based on crosslinked sulphonated fluorinated polystyrenes (PS) were synthesised in two steps. First, azide‐telechelic polystyrene was obtained by iodine transfer polymerisation of styrene in the presence of 1,6‐diiodoperfluorohexane followed by azido chain‐end functionalisation. Then azide‐telechelic polystyrene was efficiently crosslinked with 1,10‐diazido‐1H,1H,2H,2H,9H,9H,10H,10H‐perfluorodecane under UV irradiation. After 45 min only, almost completion of azide crosslinking could be achieved, resulting in crosslinked membranes with insoluble fractions higher than 95%. The sulphonation of the crosslinked membranes afforded ionic exchange capacities (IECs) ranging from 2.2 to 3.2 meq g^–1. The hydration number was shown to be very high (from 30 to 75), depending on both the content of perfluorodecane and of sulphonic acid groups. The morphology of the membranes, assessed by small‐angle X‐ray scattering, was found to be a lamellar‐type structure with two types of ionic domains. For the membrane that exhibited an IEC value of 2.2 meq·g^–1, proton conductivity was in the same range as that of Nafion® (120–135 mS·cm^–1), whereas the membrane IEC value of 3.2 meq·g^–1 showed a proton conductivity higher than that of Nafion® in liquid water from 25 to 80 °C, though a high water uptake.     

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.     

用于高温质子交换膜燃料电池的聚合物电解质膜研究进展

高温质子交换膜燃料电池在降低燃料电池水热管理复杂性、催化剂中毒方面有明显优势;可改善电池阴阳两极尤其是阴极氧气还原反应的动力学特性,提高电池的效率。聚合物电解质膜作为关键材料之一,在高温时易失水导致质子传导率降低、机械强度和热稳定性不高等问题。本文基于磺酸、磷酸和离子液体等不同质子传递介质,对高温聚合物电解质膜进行综述,比较了各类聚合物电解质膜的优缺点及应用时存在的问题,着重探讨嵌段共聚物在高温聚合物电解质膜方面的潜在应用,指出离子液体的添加不但可作为质子载体,而且在构建嵌段聚合物结构方面可发挥"诱导剂"作用。提出通过分子设计可更好了解嵌段聚合物的空间构效关系,进而通过结构设计提高膜的质子传导性能和稳定性。     

Synthesis and characterization of a novel highly phosphonated water-insoluble polymer

A novel polymer, functionalized by tetrafluoroaryl phosphonic acid units, was prepared by free-radical polymerization of the corresponding styrene monomer. The obtained polymer was analyzed by gel permeation chromatography, differential scanning calorimetry, and spectroscopy (NMR, IR). Ion exchange capacity of the water-insoluble polymer was determined in methanol solution by titration with 0.1M NaOH. The proton conductivity of the polymer of 9.91 × 10⁻⁷ S cm⁻¹ as disclosed by electrochemical impedance spectroscopy renders this polymer a promising candidate for solid electrolyte applications or as a water-insoluble dopant for proton exchange membrane applications. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48235.     

Proton conducting polydimethylsiloxane/metal oxide hybrid membranes added with phosphotungstic acid(II)

Flexible polymer electrolyte membranes consisting of zirconia (titania) and polydimethylsiloxane (PDMS) with the different molecular mass of 4500 and 600 have been synthesized by sol-gel processes. The polymeric membranes showed thermal stability and flexibility up to 300 °C due to the presence of cross-linkable inorganic nano-phase in the hybrid macromolecular matrix. The membrane becomes proton conducting polymer electrolyte by addition of 12-phosphotungstic acid (PWA). The conductivity increased up to 7.7×10⁻² S/cm through ultrasonic treatment on the membrane, which is in the application level to polymer electrolyte fuel cells. The hybrid materials can be recognized as new, low cost and environment friendly electrolyte membranes.     

Characterization of sulfonated poly(styrene-co-pyrrolidone) pore-filling membranes for fuel cell applications

Pore-filling membranes using three monomers, i.e., styrene, N-vinyl pyrrolidone (VP), and divinylbenzene (DVB), are prepared for polymer electrolyte fuel cell (PEFC) applications. A porous polyethylene (PE) film substrate is used to enhance the dimensional stability of the prepared membranes. The proton conductivity and the water uptake of the styrene/VP/DVB membranes are similar to those of the styrene/DVB membranes, even though their ion exchange capacity is slightly lesser than that of the styrene/DVB membranes. Furthermore, the thermal stability of the styrene/VP/DVB membranes is higher than that of the styrene/DVB membranes, and, for the same DVB content, the membranes containing VP exhibit better oxidative stability. VP increases the membrane’s water-absorbing ability due to its intrinsic hydrophilic property and decreases weak α-hydrogen derived from the sulfonated styrene. Finally, the membrane-electrode assembly (MEA) using the 80/10/10 (Styrene/VP/DVB in weight percentage) membrane shows better performance than that using the 90/0/10 membrane.     

Cost effective cation exchange membranes: A review

This paper will look at developments of new polymer electrolyte membranes to replace high cost ion exchange membranes such as Nafion^®, Flemion^® and Aciplex^®. These perfluorinated polymer electrolytes are currently the most commercially utilized electrolyte membranes for polymer electrolyte fuel cells, with high chemical stability, proton conductivity and strong mechanical properties. While perfluorinated polymer electrolytes have satisfactory properties for fuel cell applications, they limit commercial use due to significant high costs as well as reduced performance at high temperatures and low humidity. A promising alternative to obtain high performance proton-conducting polymer electrolyte membranes is through the use of hydrocarbon polymers. The need for inexpensive and efficient materials with high thermal and chemical stability, high ionic conductivity, miscibility with other polymers, and good mechanical strength is reviewed in this paper. Though it is difficult to evaluate the true cost of a product based on preliminary research, this paper will examine several of the more promising materials available as low cost alternatives to ion exchange membranes. These alternative membranes represent a new generation of cost effective electrolytes that can be used in various ion exchange systems. This review will cover recent and significant patents regarding low cost polymer electrolytes suitable for ion exchange membrane applications. Promising candidates for commercial applications will be discussed and the future prospects of cost effective membranes will be presented.     

Proton conducting polydimethylsiloxane/zirconium oxide hybrid membranes added with phosphotungstic acid

Inorganic polymer based hybrid membranes consisting of zirconium oxide and polydimethylsiloxane (PDMS) have been synthesized by sol-gel processes. The organic/inorganic polymeric hybrid membranes showed thermal stability and flexibility up to 300 °C. The membrane becomes proton conducting polymer electrolyte when added with 12-phosphotungstic acid (PWA). The conductivity of the membranes was measured in the temperature range from room temperature to 150 °C under saturated humidity and a maximum conductivity of 5×10⁻⁵ S cm⁻¹ was obtained at 150 °C.     

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.