Polybenzimidazole‐graft‐polyvinylphosphonic acid—proton conducting fuel cell membranes

A new method for the preparation of polybenzimidazole (PBI)‐based membranes, containing high concentrations of immobilized phosphonic acid groups, has been developed. The procedure used is carried out in two steps: (1) Synthesis of modified PBIs, containing 1,2‐dihydroxypropyl groups and preparation of films there from; (2) Introduction of vinylphosphonic acid (VPA) and initiator (cerium ammonium nitrate) in the film, subsequent grafting of VPA from the active sites of the PBI backbone. Membranes with different length of the grafted polyvinylphosphonic acid chains were prepared. The molar ratio grafted VPA units per PBI repeating unit reaches 7.8. Proton conductivity was measured at 120°C and relative humidity (RH) 20–100%. For the membrane with highest concentration of phosphonic acid groups the proton conductivity was 35 mS cm^?1 at 100% RH and 8 mS cm^?1 at 20% RH. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Basicity‐based screening of aniline derivative for composite proton exchange membranes

The aim of this study was to find a suitable aniline derivative to develop composite sulfonated poly(ether ether ketone) (SPEEK) membranes and detail evaluation of their physico‐ and electrochemical properties. The hypothesis was high basicity of the aniline derivatives could form good composite membranes with better physicochemical and electrochemical properties. To assess the basicity we measured the zeta potentials of the polymers and correlated them with ion‐exchange capacities, water uptakes, transport numbers, water‐diffusion coefficients, conductivities, and methanol permeabilities. The obtained values of zeta potentials at pH 7 were 6.52, ?14.66, ?25.17, and ?28 for SPEEK/polynaphthalene (PNAPH), SPEEK/polyanisidine (PANIS), SPEEK/polyaniline (PANI), and SPEEK/polyxylindine (PXYL), respectively supports the hypothesis and strongly suggests polyaniline derivative's basicity‐dependent properties. Of the four derivatives (PNAPH, PANIS, PANI, and PXYL), the SPEEK/PXYL composite membrane had the lowest methanol permeability of 1 × 10^?4 cm²/s and highest proton conductivity of 161 mS/cm. These values are far better than the neat SPEEK and SPEEK/PANI composite. The suitability of SPEEK/PXYL can be explained by the high basicity of the PXYL composite membrane, which leads to the formation of effective Debye spheres, meaning that the ionic complex can interact with surrounding hydronium ions and form hydrophilic channels resulting in high proton conductivity and low methanol permeability. These results suggest that SPEEK/PXYL is a highly suitable membrane for methanol fuel cells or other electrochemical applications. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43978.     

Vinyl‐addition type norbornene copolymers containing flexible spacers and sulfonated pendant groups for proton exchange membranes

Novel sulfonated poly(2‐butoxymethylenenorbornene‐co‐2‐(6‐phenoxy‐hexyloxymethylene)‐5‐norbornene [sP(BN/PhHN)] were prepared successfully through vinyl‐addition type polymerization and then sulfonated with concentrated sulfuric acid (98%) as sulfonating agent in a component solvent. The sP(BN/PhHN)‐40 with the maximal degree of sulfonation of 40% can be obtained by controlling the sulfonating reaction time from 8 to 20 h, and a proton conductivity of 3.35 × 10^?3 S/cm was achieved at 70°C. The methanol permeabilities of these membranes were in the range from 0.26 to 6.58 × 10^?7 cm²/s, which were remarkably lower than Nafion (2.36 × 10^?6 cm²/s). TEM analysis revealed that these side‐chain type membranes have a microphase separated structure composed of hydrophilic side‐chain domains and hydrophobic polynorbornene main chain domains. Sulfonated polynorbornene containing soft spacers displayed better properties, such as lower water uptake, high thermal properties, mechanical properties, and low methanol permeability. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Crosslinking of polybenzimidazole membranes by divinylsulfone post‐treatment for high‐temperature proton exchange membrane fuel cell applications

Phosphoric acid‐doped polybenzimidazole (PBI) has been suggested as a promising electrolyte for proton exchange membrane fuel cells operating at temperatures up to 200 °C. This paper describes the development of a crosslinking procedure for PBI membranes by post‐treatment with divinylsulfone. The crosslinking chemistry was studied and optimized on a low‐molecular‐weight model system and the results were used to optimize the crosslinking conditions of PBI membranes. The crosslinked membranes were characterized with respect to chemical and physiochemical properties, showing improved mechanical strength and oxidative stability compared with their linear analogues. Fuel cell tests were further conducted in order to demonstrate the feasibility of the crosslinked membranes. Copyright © 2011 Society of Chemical Industry     

A methanesulfonic acid/sulfuric acid‐based route for easily‐controllable chloromethylation of poly(ether ether ketone)

A mixed methanesulfonic acid/sulfuric acid solvent based chlromethylation of poly(ether ether ketone) (PEEK) is described. Methanesulfonic acid is the solvent, sulfuric acid is the catalyst, and chloromethyl octyl ether (CMOE) is the chloromethylating reagent. ¹H‐NMR spectra confirmed the successful synthesis of chloromethylated PEEK (CMPEEK). The effects of polymer concentration, catalyst/polymer ratio, and reaction temperature on the rate of PEEK chloromethylation were investigated. In order to minimize crosslinking, the PEEK concentration must be kept very low (< 2%). The reaction rate increases with increased catalyst/polymer ratio and reaction temperature. The activation energy of PEEK chloromethylation is 30.9 kJ mol^?1. The extent of reaction for the new route is more easily controllable as compared with the previous sulfuric acid based route. The reaction rate constant at 25°C for the new route is 1.29 h^?1 which is lower than that for chloromethylation by concentrated sulfuric acid at ?10°C (rate constant 1.88 h^?1). As a result, the degree of chloromethylation of CMPEEK can be easily controlled at room temperature using this mixed solvent. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41404.     

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 proton conductivity studies of methacrylate/methacrylamide‐based azole functional novel polymer electrolytes

Anhydrous polymer electrolytes based on azole functional methacrylates and methacrylamides have been produced for use in proton exchange membrane fuel cells (PEMFCs). Poly(methacryloyl chloride) (PMAC) was prepared first by free‐radical polymerization of methacryloyl chloride, followed by side chain functionalization with 5‐aminotetrazole (ATet), 3‐amino‐1,2,4‐triazole (ATri) and 1H‐1,2,4‐triazole (Tri). Finally, the obtained polymers were doped with triflic acid (TA) at stoichometric ratios of 1.0, 2.0 and 4.0 with respect to azole units, and the anhydrous polymer electrolytes were obtained. The membranes were characterized by FT‐IR, ¹³C‐NMR, and elemental analysis. Thermal behaviour of polymers was explored by TGA and DSC. The samples were thermally stable up to approximately 200 ^oC. Proton conductivity was measured by impedance spectroscopy. Trifilic acid doped poly(methacryloyl aminotetrazole) (PMAATet‐(TA)₄), poly(methacryloyl‐3‐amino‐1,2,4‐triazole) (PMA‐Tri‐(TA)₄), and poly(methacryloyl‐1,2,4‐triazole) (PMA‐ATri‐(TA)₄) showed maximum proton conductivities of 0.01 Scm^?1, 0.02 Scm^?1 and 8.7x10^?4 Scm^?1, respectively, at 150^°C and anhydrous conditions. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39915.     

Branched poly(biphenylene-co-sulfone)ether ion exchange membranes containing perfluorocyclobutane groups for fuel cell applications

A series of branched poly(biphenylene-co-sulfone) ion exchange membranes containing perfluorocyclobutane groups were prepared for fuel cells. Two bifunctional trifluorovinyloxy-terminated monomers (sulfonable 4,4′-bis(trifluorovinyloxy)biphenyl and insulfonable 4,4′-sulfonyl-bis(trifluorovinyloxy)biphenyl) and a trifunctional trifluorovinyloxy-terminated branching agent (1,1,1-tris(4′-trifluorovinyloxyphenyl)ethane) were synthesized and terpolymerized via thermal [2π + 2π] cyclodimerization to obtain partially fluorinated and branched polymers containing 0–5 mol% of the branching agent. They were then postsulfonated by chlorosulfonic acid at room temperature, cast as membranes, and characterized to evaluate their electrochemical properties for fuel cell applications. As the branching agent content was increased, their polydispersity values highly increased, indicating they became highly branched. It was confirmed that higher branching agent content also increased the ion exchange capacity, water uptake, and proton conductivity of the branched ion exchange membranes containing perfluorocyclobutane groups. This indicates that their electrochemical properties can be easily controlled by the degree of branching. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48373.     

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

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

Quaternized poly(2.6 dimethyl‐1.4 phenylene oxide)/polysulfone blend composite membrane doped with ZnO‐nanoparticles for alkaline fuel cells

A series of quaternized poly(2.6 dimethyl‐1.4 phenylene oxide)/polysulfone (QPPO/PSF) blend anion exchange membrane (AEM) were successfully fabricated and characterized for alkaline fuel cell application. Zinc oxide (ZnO) nanoparticles were introduced in the polymer matrix to enhance the intrinsic properties of the AEM. To confirm successful fabrication, Fourier‐transform infrared spectroscopy and nuclear magnetic resonance (¹H‐NMR) were used. The membrane properties were enhanced by the addition of ZnO nanoparticles. The addition of ZnO nanoparticles resulted to a higher ion exchange capacity (IEC) of 3.72 mmol g^?1, increase of ion conductivity (IC) up to 52.34 mS cm^?1 at 80 °C, enhancement of water uptake, and reduced methanol permeability. The QPPO/PSF/2% ZnO composite retained over 80% of its initial IC at room temperature and also retained over 50% of its initial IC at 80 °C when evaluated for alkaline stability. The maximum power output reached for the membrane electrode assembly constructed with QPPO/PSF/2%ZnO was 69 mW cm^?2 at room temperature, which is about three times more than the parent QPPO membrane. The above results indicate that QPPO/PSF/ZnO is a good candidate as an AEM for fuel cell application. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45959.     

Montmorillonite‐reinforced sulfonated poly(phthalazinone ether sulfone ketone) nanocomposite proton exchange membranes for direct methanol fuel cells

To produce a composite membrane with high conductivity and low permeability, SPPESK with a degree of sulfonation of 101% was carefully selected for the preparation of montmorillonite (MMT)‐reinforced SPPESK using solution intercalation. The fundamental characteristics such as water uptake, swelling ratio, proton conductivity, methanol permeability, and mechanical properties of the composite membranes were studied. Water uptake is improved when organic MMT (OMMT) loading increase. The composite membranes with CTAB‐MMT loading of 4–0.5% show 0.143–0.150 S cm^?1 proton conductivity at 80°C, which approaches the value of Nafion112. In addition, methanol permeability was decreased to 6.29 × 10^?8 cm² s^?1 by the addition of 6 wt % OMMT. As a result, the SPPESK‐MMT composite membrane is a good candidate for use in direct methanol fuel cells. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39852.     

Multi-cation side-chain-type containing piperidinium group poly(2,6-dimethyl-1,4-phenylene oxide) alkaline anion exchange membranes

A series of alkaline anion exchange membranes (AAEMs) based on poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) with multi-cation side chain containing piperidinium group were fabricated via nucleophilic substitution and Menshutkin reaction. The chemical structures of the AAEMs (PPO-AMP-X) were determined by Fourier transform infrared and proton nuclear magnetic resonance spectra. The resultant PPO-AMP-X membranes with the ion exchange capacities (IECs) of 2.05–2.77 mmol g⁻¹ displayed the hydroxide conductivities in the range of 61.04–78.92 mS cm⁻¹ at 80°C. When tested at the same degree of functionalization levels, the PPO-AMP-X membranes exhibited significantly higher hydroxide conductivity and lower conductivity loss than conventional AAEMs bearing benzyltri-methylammonium group (PPO-TMA). The PPO-AMP-28 multi-cation membrane showed a hydroxide conductivity of 70.52 mS cm⁻¹ at 80°C, which was nearly two times higher than that of the PPO-TMA-28 single-cation membrane (36.74 mS cm⁻¹). Compared with PPO-TMA-28 (56.76% decrease), the hydroxide conductivity of PPO-AMP-28 merely decreased by 23.15% after soaked in 1 M KOH at 80°C for 500 h. Additionally, the PPO-AMP-X membranes displayed moderate mechanical properties and good thermal stabilities, which can meet the basic requirements for use in fuel cells. This study provides a facile method for preparing AAEMs with multi-cation side chain containing piperidinium group.     

Sulfonated poly(styrene)s‐PBIOO® blend membranes: Thermo‐oxidative stability and conductivity

Low‐cost polymers poly(styrene) and poly(α‐methylstyrene) have been sulfonated followed by blending with PBIOO® (30 wt % sulfonated ionomer, 70 wt % PBIOO). At this polymer ratio the sulfonated ionomer served as the macromolecular acidic cross‐linker which led to enhancement of the PBIOO stability. Both membrane types were treated with Fenton's Reagent to investigate their resistance to oxidation and radical attack. Indeed, the blend membranes showed enhanced stability in oxidative conditions compared to the pure PBIOO membranes. Furthermore, the sulfonated poly(α‐methylstyrene)‐PBIOO blend membrane showed less weight loss during and after Fenton's Test than the corresponding poly(styrene sulfonic acid)‐PBIOO membrane. Assuming all the characteristics of the blend membrane before and after the Fenton's Test, we concluded for a partial degradation of both sulfonated poly(styrene)s, whereas they remain in the blend membrane matrix due to the acid‐base crosslinking. Thus, since the sulfonated poly((α‐methyl)styrene)‐PBIOO blend membranes conserved their integrity even after Fenton's Test they can be regarded as potential low‐cost high‐T fuel cell membranes. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39889.     

A new synthesis approach for proton exchange membranes based on ultra-high-molecular-weight polyethylene

A new approach for gas-phase modification of ultra-high-molecular-weight polyethylene (UHMWPE) film for synthesis of proton exchange membranes (PEMs) has been successfully realized. First, the membrane precursors have been prepared by soaking the films in a monomers/AIBN solution followed by their modification with polystyrene (PS) in styrene vapor at 110°C. The developed method is characterized by high efficiency, simplicity, and ecological purity. The modified UHMWPE films containing up to 60 wt% of PS have been obtained. Then, PEMs were prepared by sulfonation of these precursors. According to energy-dispersive X-ray spectroscopy of the sulfonated samples, almost uniform distribution of PS through the film thickness was observed. The membranes with an ion exchange capacity up to 2.7 mmol/g and proton conductivity up to 60 mS/cm (water, 25°C) were obtained. Comparative tests of the obtained UHMWPE-sulfonated PS and commercial Nafion-115 membranes in a hydrogen–air fuel cell have been carried out. It has been shown that the cell with the synthesized membranes exhibits better performance than that with Nafion-115.     

A new sulfonated poly(ether sulfone) hybrid with low humidity dependence for high‐temperature proton exchange membrane fuel cell applications

A new sulfonated poly(ether sulfone) (PES) hybrid with low humidity dependence was prepared based on a new synthesized PES and Udel as a commercial PES. The PES was synthesized based on a pyridine containing diol which is able to change between pyridine and pyridinium salt forms during the cell performance (acidic condition) and facilitate proton transfer. The presence of nitrogen group increases inter and intramolecular interactions in the membrane and enhance proton hopping mechanism. Thermogravimetrical analysis of PES hybrid shows good thermal stability. Proton conductivity measurements were evaluated on a fuel cell test station, showing that the membrane has better performance under lower humidity (relative humidity = 60%) compare to the fully hydrated condition (relative humidity = 100%). The results reveal that proton transfer might be mainly accomplished through proton hopping mechanism at higher temperatures. The membrane also shows significant proton conductivity at 120 °C (about 6.6 mS cm^?1 at RH = 30%). © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 45342.     

Modification of SPPESK proton exchange membranes through layer‐by‐layer self‐assembly

Sulfonated poly(phthalazinone ether sulfone ketone) (SPPESK) composite membranes are fabricated through electrostatic layer‐by‐layer (LbL) self‐assembly method with chitosan (CS) and phosphotungstic acid (PWA) to enhance the proton conductivity and stability. The results demonstrate that LbL self‐assembly has different effects on the SPPESK membrane substrates with different sulfonation degrees (DSs). It elevates proton conductivity of the SPPESK membrane of lower DS and enhances swelling stability of the SPPESK membrane of higher DS. For instance, at 80°C, proton conductivity of the SPPESK0.74/(CS/PWA)₁ membrane (lower DS) increases by 16%–96.49 mS cm^?1, and swelling ratio of the SPPESK1.01/(CS/PWA)₃ membrane (higher DS) decreases from 58 to 29%. Attribute to the electrostatic interaction and ion cross‐linking networks, permeability of the SPPESK0.74/(CS/PWA)₃ membrane and the SPPESK1.01/(CS/PWA)₅ membrane are reduced by 45 and 30%, respectively. The results indicate that the LbL self‐assembly has broadened the available DS range for fuel cell applications. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 132, 42867.     

Preparation and characterization of novel grafted cellophane‐phosphoric acid‐doped membranes for proton exchange membrane fuel‐cell applications

This work concerns preparation of acid‐base polyelectrolyte membranes for fuel‐cell applications from cellulosic backbones for the first time. Grafted cellophane‐phosphoric acid‐doped membranes for direct oxidation methanol fuel cells (DMFC) were prepared following three steps. The first two steps were conducted to have the basic polymers. The first step was introducing of epoxy groups to its chemical structure through grafting process with poly(glycidylmethacrylate) (PGMA). The second step was converting the introduced epoxy groups to imides groups followed by phosphoric acid (? PO₃H) doping as the last step. This step significantly contributes to induce ion exchange capacity (IEC) and ionic conductivity (IC). Chemical changes of the cellophane composition and morphology characters were followed using FTIR, TGA, and SEM analysis. Different factors affecting the membranes characters especially IEC, methanol permeability, and thermal stability were investigated and optimized to have the best preparation conditions. Compared to Nafion 117 membrane, cellophane‐modified membranes show a better IEC, less methanol permeability, and better mechanical and thermal stability. IEC in the range of 1–2.3 meq/g compared to 0.9 meq/g per Nafion was obtained, and methanol permeability has been reduced by one‐order magnitude. However, the maximum obtained IC for cellophane‐PGMA‐grafted membrane doped with phosphoric acid was found 2.33 × 10^?3 (S cm^?1) compared to 3.88 × 10^?2 (S cm^?1) for Nafion 117. The obtained results are very promising for conducting further investigations taking into consideration the very low price of cellophane compared to Nafion. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Preparation and proton conductivity of phosphoric acid‐doped blend membranes composed of sulfonated block copolyimides and polybenzimidazole

A series of phosphoric acid (PA)‐doped blend membranes composed of block or random sulfonated polyimides (SPIs) and polybenzimidazole (PBI) were prepared with similar PA contents to investigate the influence of chemical structures of SPIs on proton conductivity. The proton conductivity of a PA‐doped blend membrane containing block‐type SPI, PA‐bSPI(80/20)/oPBI, was higher than that of the corresponding pristine block‐type SPI, PA‐SPI/PBI containing random‐type SPI and Nafion membranes over a wide temperature range, and reached 0.37 S cm^?1 at 90 °C and 98% relative humidity. The PA‐bSPI(80/20)/oPBI membrane also showed distinct proton conductivity even at low humidity due to a new proton transport pathway among PA and sulfonic acid groups. Also, the novel PA‐doped blend membrane showed higher proton conductivity than Nafion at both above 100 °C and below 0 °C under low relative humidity conditions. © 2013 Society of Chemical Industry     

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.     

Polyacrylonitrile‐based proton conducting membranes containing sulfonic acid and tetrazole moieties

Proton conducting membranes based on polymers containing sulfonic acid and tetrazole moieties were developed. Successful syntheses of poly(acrylonitrile‐co ‐styrene sulfonic acid) (PAN‐co ‐PSSA), poly(acrylonitrile‐co ‐5‐vinyl tetrazole) (PAN‐co ‐PVTz), and poly(acrylonitrile‐co ‐5‐vinyl tetrazole‐co ‐styrene sulfonic acid) (PAN‐co ‐PVTz‐co ‐PSSA) were confirmed by ¹H‐nuclear magnetic resonance spectroscopy, elemental analysis, and Fourier transform infrared spectroscopy. Two approaches were performed to study the effects of molar ratio of sulfonic acid to tetrazole and tetrazole content on membrane properties. In the first approach, PAN‐co ‐PSSA was blended with PAN‐co ‐PVTz at three molar ratios. The second approach focused on PAN‐co ‐PVTz‐co ‐PSSA membranes with various tetrazole contents. PAN‐co ‐PSSA membrane was also prepared. All solution‐cast membranes were hydrolytically stable, except for PAN‐co ‐PVTz‐co ‐PSSA with 71% tetrazole. Surface morphologies of blend membranes were studied using scanning electron microscopy, and no phase separation was observed. Water uptake was shown to increase with increasing tetrazole. All membranes exhibited high thermal stability (up to 250 °C) and high storage moduli. Proton conductivity was found to depend significantly on relative humidity. The influences of sulfonic acid to tetrazole ratio and tetrazole content on proton conduction were observed and discussed. A maximum proton conductivity of 7.1 × 10^?3 S/cm at 26 °C was obtained from PAN‐co ‐PSSA membrane. In addition, all tested membranes showed relatively good oxidative stability after treatment in Fenton's reagent. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 45411.