Elsevier

Journal of Membrane Science

Volume 341, Issues 1–2, 30 September 2009, Pages 155-162
Journal of Membrane Science

Blends based on sulfonated poly[bis(benzimidazobenzisoquinolinones)] and poly(vinylidene fluoride) for polymer electrolyte membrane fuel cell

https://doi.org/10.1016/j.memsci.2009.06.002Get rights and content

Abstract

A new blend system consisting of an amorphous sulfonated poly[bis(benzimidazobenzisoquinolinones)] (SPBIBI) and the semi-crystalline poly(vinylidene fluoride) (PVDF) was prepared for proton exchange membranes. The miscibility behavior of a series of blends of SPBIBI with PVDF at various weight ratios was studied by WXRD, DSC and FTIR. The properties of the blend membranes were investigated, and it was found that the introduction of PVDF in the SPBIBI matrix altered the morphological structure of the blend membranes, which led to the formation of improved connectivity channels. For instance, the conductivity of the blend membrane containing 10 wt% PVDF displayed the highest proton conductivity (i.e., 0.086 S cm−1) at room temperature, a value almost twofold that of the pristine SPBIBI membranes (i.e., 0.054 S cm−1) under identical conditions. The result was thus comparable to the proton conductivity of Nafion 117 (i.e., 0.09 S cm−1). Moreover, the dimensional stability, the elongation at break, the methanol permeability and the oxidative stability were enhanced in various extents by introducing PVDF into the blend membranes.

Introduction

Polymer electrolyte membranes (PEMs) constitute an important class of polymeric materials for use as ion-exchangers, electrolytes for batteries and sensors, and dopants for electronic conductors. Recently, studies on PEM materials have been strongly promoted as a result of a considerable interest in the development of high-performance polymer electrolyte membrane fuel cells (PEMFCs) for transportation, stationary and portable power applications [1], [2]. In order for a fuel cell to work effectively and to be widely adapted, the PEM must present a portfolio of properties including an acceptable cost, a high proton conductivity, good chemical and thermal stabilities, a decent mechanical strength, and a low fuel crossover [3].

Nafion (from Dupont) is a perfluorosulfonated membrane material with a hydrophobic fluorocarbon backbone and hydrophilic sulfonic pendent side-chains, and is capable of satisfying a large number of the requirements concerning polymer electrolyte membranes. Nafion has found practical use in PEMFCs [4]. However, various limitations exist for Nafion membranes, and these include a very elevated cost, a high fuel permeability, and the loss of the preferable properties at temperatures >80 °C [5], [6], [7], [8], [9].

In view of this, numerous efforts have been focused on developing more economical alternatives based on non-fluorinated or partially fluorinated polymers. Up to now, a large number of sulfonated aromatic polymers such as poly(ether ether ketone) [10], [11], [12], [13], [14], poly(ether sulfone)s [15], [16], [17], [18], poly(arylene ether)s [19], [20], polyimides [21], [22], [23], [24], [25], [26] and poly(p-phenylene)s [27], [28], [20] have been developed. Generally, such polymer membrane materials for PEM fuel cells rely on the presence of absorbed water and its interaction with acid groups to produce proton conductivity. To ensure high proton conductivity, polymers presenting significant ion-exchange capacities (IECs) have been utilized, but these materials were found to swell excessively in water (thereby losing their mechanical properties) and were moreover brittle when dry.

Previous papers [29] have reported on poly[bis(benzimidazobenzisoquinolinones)] ionomers, a class of ladder polymers, that are hydrolytically and dimensionally stable. This enhanced stability toward water has been attributed to the acid–base interactions between the pyridinone ring and sulfonic acid groups. However, the proton conductivity and oxidative stability for practical applications requires further improvement. The present study thus attempts to investigate the possibility of obtaining, through blending, a membrane demonstrating high proton conductivity as well as high oxidative stability.

Polymer blending has been known to be the most frequently used means of overcoming the shortcomings of an individual polymer and of obtaining inexpensive materials with desirable properties by combining the advantages of two or more individual polymer components. A key factor in acquiring polymer electrolyte membranes via blending relies on finding an optimum combination of thermal, chemical and mechanical properties with hydrophilicity in the employed polymers. Among various counter-polymers, poly(vinylidene fluoride) (PVDF), a semi-crystalline and chemically resistant material, is well suited for the fuel cell environment [30]. Blends of PVDF with Nafion [31], [32] and sulfonated poly(ether ether ketone) [33], [34] have been prepared for potential use in a direct methanol fuel cell. PVDF also demonstrates sufficient dimensional stability and mechanical strength. Thus, a successful combination of the conducting characteristics of SPBIBI and the physical stability of PVDF should be able to be achieved provided that it is possible to obtain a miscible blend of the two materials.

The present article reports on a blend of SPBIBI with PVDF for use as a proton exchange membrane for fuel cells. The effect of the PVDF content on water uptake, swelling ratio, oxidation stability, proton conductivity and methanol permeability of the prepared SPBIBI/PVDF membranes were investigated to evaluate their potential applications in direct methanol fuel cells (DMFCs).

Section snippets

Materials

PVDF was purchased from Aldrich having a weight average molecular weight (Mw) of 530,000. Dimethylsulfoxide (DMSO) was dried over CaH2, then distilled under reduced pressure, and stored over 4 Å molecular sieves under nitrogen in the dark. 4,4′-Binaphthyl-1,1′,8,8′-tetracarboxylic dianhydride disulfonic acid (SBTDA) was prepared according to a previously reported method [35]. All other reagents were obtained from commercial sources and used as received.

Synthesis of SPBIBI

The sulfonated

Compatibility of the blend

The optical clarity of the membranes was visually inspected as a preliminary means of identifying the compatibility between the polymers. PVDF, a semi-crystalline and chemically resistant polymer, is white and opaque. The blend membranes were denoted as SPBIBI/PVDF(χ), where χ is the weight ratio of PVDF in the feed. As shown in Fig. 1, all blend membranes were transparent, and when increasing the content of PVDF, the color turned from burgundy to light red.

The compatibility of the two polymer

Conclusions

Partially fluorinated membranes based on blends of SPBIBI and PVDF were successfully prepared with a solution casting method. The results of WXRD and DSC indicated that the blend membranes showed a decent compatibility within a broad range of compositions up to approximately 70% of PVDF. The blends could produce good ion conduction channels especially when the blend contained 10% of PVDF. This gave rise to a high proton conductivity. The dimensional stability, the elongation at break, the

Acknowledgements

We thank the National Basic Research Program of China (No. 2009CB623401), the National Science Foundation of China (Nos. 50673087 and 50825303) and the Development of Scientific and Technological Project of Jilin Province (No. 20080620) for the financial support.

References (39)

Cited by (18)

  • Sulfonated polyvinylidene fluoride and functional copolymer based blend proton exchange membrane for fuel cell application and studies on methanol crossover

    2021, Renewable Energy
    Citation Excerpt :

    On the other hand, PEM-5 and PEM-6 which were prepared from the blend of S-PVDF and PMMA-co-PAMPS-1 exhibited single Tg around 105 °C and do not show any Tm due to loss of crystallinity after sulfonation of PVDF (Fig. 5B). This proves that after sulfonation the nature of crystallinity changes and better intermolecular interaction between –SO3H of S-PVDF and PMMA-co-PAMPS-1 exists in PEM-5 and PEM-6 [26,27]. Fig. 6 shows the XRD pattern of PVDF, S-PVDF, and PEM-3, PEM-4, PEM-5, and PEM-6 membranes.

  • Highly durable phosphonated graphene oxide doped polyvinylidene fluoride (PVDF) composite membranes

    2020, International Journal of Hydrogen Energy
    Citation Excerpt :

    PVDF/Arkema M43, Nafion/PVDF blend membranes were applied to increase the operation time and proton conductivity [24,25]. The sulfonated hydrocarbon polymers blended with PVDF polymer demonstrate decreasing membrane electrode assembly (MEA) resistivity [26], enhanced oxidative, dimensional stability [27] and improved water management [28]. The polybenzimidazole/PVDF blends illustrate lower swelling [29].

  • Molecular dynamics simulation study of carboxylated and sulfonated poly(arylene ether sulfone) membranes for fuel cell applications

    2015, International Journal of Hydrogen Energy
    Citation Excerpt :

    Proton exchange membrane (PEM) is an important part of PEMFC that conducts the protons generated in the anode to the cathode and prevents occurrence of two processes, namely (i) the passage of electron and (ii) the crossover of the fuel (O2 and H2) [7–9]. Perfluorinated membrane such as Nafion, due to high proton conductivity and good stability, is a commonly used polymer as fuel cell membrane, but it has some disadvantages such as; high production cost, low proton conductivity as a result of dehydration at high temperatures (T > 80 °C) and poor resistance to methanol crossover in the direct methanol fuel cells [10–14]. Sulfonated aromatic polymers such as sulfonated poly(ether ether ketone) (SPEEK), sulfonated poly(phenylene sulfide), sulfonated poly(arylene ether sulfone) (SPAES), sulfonated poly imide (SPI) due to their high proton conductivity, thermal and mechanical stability and low production cost, are considered as favorable alternatives to the Nafion [9,11,15–17].

  • Sulfonated poly(arylene ether sulfone) membranes blended with hydrophobic polymers for direct methanol fuel cell applications

    2014, International Journal of Hydrogen Energy
    Citation Excerpt :

    The endothermic peaks of the PVdF blend membrane decreased with increasing content of PVdF in the SPAES solutions. These results confirmed that it is possible to blend SPAES and PVdF on the basis of their high compatibility [13–16]. In a blend system, insufficient interaction between two components, which manifests as heterogeneous morphology, is not conducive to achieving high performance.

  • Effect of composition on the properties of PEM based on polybenzimidazole and poly(vinylidene fluoride) blends

    2014, Polymer
    Citation Excerpt :

    Poly(vinylidene fluoride) (PVDF) is a semi-crystalline, hydrophobic and an engineering thermoplastic that offers many favorable properties like durability, mechanical integrity, thermal and chemical stability and chemical resistance – properties a PEM ought to have for use in fuel cells. In fact, blends of PVDF with a variety of polymers including Nafion, sulfonated poly (ether ketone), poly[bis(benzimidazobenzisoquinolinones)] and styrene–ethylene/butylene–styrene thermoplastic elastomer were developed for PEMFC applications [15–20]. In our previous work, we had reported a new blend system consisting of amorphous PBI and semi-crystalline PVDF that was obtained by dissolving the two polymers in dimethyl acetamide (DMAc) [21].

View all citing articles on Scopus
View full text