Membranes For Direct Methanol Fuel Cells Research Articles

Evaluation of sulfonated polysulfone/zirconium hydrogen phosphate composite membranes for direct methanol fuel cells

Direct methanol fuel cell (DMFC) technology has advanced perceivably, but technical challenges remain that must be overcome for further performance improvements. Thus, in this study, sulfonated polysulfone/zirconium hydrogen phosphate (SPSf/ZrP) composite membranes with various sulfonation degrees (20%, 35%, and 42%) and a constant concentration of ZrP (2.5%) were prepared to mitigate the technical challenges associated with the use of conventional Nafion® membranes in DMFCs. The composite membranes were investigated through Scanning Electron Microscopy (SEM), Electrochemical Impedance Spectroscopy (EIS), Thermogravimetric Analysis (TGA), oxidative stability and water uptake measurements, and single cell testing. Comparison was also made with Nafion® 115. Single cell tests were performed under various methanol concentrations and cell temperatures. Stability characteristics of the DMFCs under charging and discharging conditions were investigated via 1200min short-term stability tests. The response characteristics of the DMFCs under dynamic conditions were determined at the start-up and shut-down stages. Composite membranes with sulfonation degrees of 35% and 42% were found to be highly promising due to their advanced characteristics with respect to proton conductivity, water uptake, thermal resistance, oxidative stability, and methanol suppression. For the whole range of parameters studied, the maximum power density obtained for SPSf/ZrP-42 (119mWcm−2) was found to be 13% higher than that obtained for Nafion® 115 (105mWcm−2).

Sulfonated holey graphene oxide paper with SPEEK membranes on its both sides: a sandwiched membrane with high performance for semi-passive direct methanol fuel cells

The sandwiched membrane which consists of the sulfonated holey graphene oxide paper with the deposition of the sulfonated poly(ether ether ketone) (SPEEK/SHGO/SPEEK) membrane on its both sides has been prepared. This membrane is reported to have higher proton conductivity (155.6±1.6mScm−1), but lower methanol permeability (7.05±0.21×10−6cm2s−1) than Nafion® 112 at 80°C, whose respective values are 138.6±1.4mScm−1 and 15.40±0.46×10−6cm2s−1, respectively. The specific structure of the SHGO comprising the sulfonated and holey graphitic plane plays an important role in the high performance of the SPEEK/SHGO/SPEEK membrane. First, the sulfonated structure could increase the overall density of the sulfonic acid groups in the membranes, which increases the number of proton exchange groups participating in the proton transport. Second, the holey structure of the SHGO provides an additional path for the proton transport, which well avoids the blockage of the proton transport by the high aspect ratio graphitic planes. Third, the sulfonated and holey structure could also increase the interlayer spacing of the graphitic planes in the SHGO paper, which would promote the proton transport as well. Finally, the presence of the SHGO paper with the layer-by-layer stacked graphitic plane would effectively retard the diffusion of methanol through the membrane. When evaluated in the semi-passive direct methanol fuel cell (DMFC), the cell with the SPEEK/SHGO/SPEEK membrane shows higher stability and exhibits a maximum power density 61.1% higher than with Nafion® 112, which strongly suggests that the SPEEK/SHGO/SPEEK membrane could be used as the proton exchange membrane for DMFCs.

Functionalized and Electrospun Polymeric Materials as High-Performance Membranes for Direct Methanol Fuel Cell: A Review

Proton exchange membranes (PEM) for a direct methanol fuel cell (DMFC) have main drawbacks which are methanol permeability, reduced proton conductivity and the cost of the membrane. This paper reviews different polymeric materials such as fluorinated, non-fluorinated, acid-base complex, and composite membranes for DMFC. Currently, nonfluorinated membranes gain a lot of attention due to their low cost. Many researchers have developed functionalization methods for non-fluorinated polymer electrolyte membranes for DMFC application to reduce the methanol crossover. Finally, this review presents the Electrospinning technique and its parameter for fabrication of PEM with functionalized polymeric materials by using electrospinning to solve the proton conductivity and methanol permeability problem. The last part of the paper describes the current studies and future direction of PEM for DMFC.

Enhancement of Hybrid SPEEK Based Polymer–Cyclodextrin-Silica Inorganic Membrane for Direct Methanol Fuel Cell Application

Direct methanol fuel cell (DMFC) is one of several types of fuel cells that use proton exchange membrane (PEM) as a liaison between the reaction at the cathode and anode. Polyether-ether ketone (PEEK) is one of the aromatic polymer that can be applied in DMFC because of its characteristics that are resistant to DMFC environment. The polymer is also quite easy in the sulfonation process using concentrated sulfuric acid. However the role of polyether-ether ketone as DMFC membrane material is still lack of advantage due to its low conductivity and therefore the modification is required to increase the value of proton conductivity of the membrane. The purpose of this experiment is to modify the membrane (sPEEK) with the addition of cyclodextrins-silica, additive variation charge of 2%, 6% and 10%, time and temperature were fixed at 4 hours and 65oC. The results showed the best results of membrane sPEEK was obtained at the addition of -cyclodextrin -silica 10% with the membrane characteristics of ion exchange capacity of 2.19 meq / g polymer, the degree of sulfonation of 81%, methanol permeability of 3.09 x 10-9 cm2 / s and water uptake membrane of 64%.Article History: Received January 18th 2017; Received in revised form April 21st 2017; Accepted June 22nd 2017; Available onlineHow to Cite This Article: Kusworo, T.D., Hakim, M.F. and Hadiyanto, H. (2017) Enhancement of Hybrid SPEEK Based Polymer–Cyclodextrin-Silica Inorganic Membrane for Direct Methanol Fuel Cell Application. International Journal of Renewable Energy Development, 6(2), 165-170.https://doi.org/10.14710/ijred.6.2.165-170

Enhancement of Hybrid SPEEK Based Polymer–Cyclodextrin-Silica Inorganic Membrane for Direct Methanol Fuel Cell Application

Direct methanol fuel cell (DMFC) is one of several types of fuel cells that use proton exchange membrane (PEM) as a liaison between the reaction at the cathode and anode. Polyether-ether ketone (PEEK) is one of the aromatic polymer that can be applied in DMFC because of its characteristics that are resistant to DMFC environment. The polymer is also quite easy in the sulfonation process using concentrated sulfuric acid. However the role of polyether-ether ketone as DMFC membrane material is still lack of advantage due to its low conductivity and therefore the modification is required to increase the value of proton conductivity of the membrane. The purpose of this experiment is to modify the membrane (sPEEK) with the addition of cyclodextrins-silica, additive variation charge of 2%, 6% and 10%, time and temperature were fixed at 4 hours and 65oC. The results showed the best results of membrane sPEEK was obtained at the addition of -cyclodextrin -silica 10% with the membrane characteristics of ion exchange capacity of 2.19 meq / g polymer, the degree of sulfonation of 81%, methanol permeability of 3.09 x 10-9 cm2 / s and water uptake membrane of 64%. Keywords: Direct Methanol Fuel Cell, Poly(ether ether ketone), cyclodextrin-silica, sulfonation, ionic conductivity.Article History: Received January 18th 2017; Received in revised form April 21st 2017; Accepted June 22nd 2017; Available onlineHow to Cite This Article: Kusworo, T.D., Hakim, M.F. and Hadiyanto, H. (2017) Enhancement of Hybrid SPEEK Based Polymer–Cyclodextrin-Silica Inorganic Membrane for Direct Methanol Fuel Cell Application. International Journal of Renewable Energy Development, 6(2), 165-170.https://doi.org/10.14710/ijred.6.2.165-170

Effect of polymer sulfonation on the proton conductivity and fuel cell performance of polyvinylalcohol‐mordenite direct methanol fuel cell membranes

AbstractSulfonated polyvinylalcohol‐mordenite (SPVA‐MOR) membranes for direct methanol fuel cell use were synthesized and characterized. It had earlier been found out that polyvinylalcohol‐mordenite (PVA‐MOR) membranes, while having excellent methanol permeability and modest proton conductivity values, had inferior direct methanol fuel cell performances than Nafion™. Sulfonating the polyvinylalcohol matrix had been suggested to improve the proton conductivity. In this work, polyvinylalcohol powder was sulfonated by using propane sultone as the sulfonating agent prior to the membrane synthesis. Morphological analyses revealed that the zeolite particles mixed homogeneously within the polymer matrix. Sulfonating the polymer slightly decreased both water and methanol uptakes. Both in PVA‐MOR and SPVA‐MOR membranes, water uptake turned out to be higher than the methanol uptake. SPVA‐MOR membranes were found to have an average proton conductivity of 0.052 S·cm−1 when compared with the 0.036 S·cm−1 of PVA‐MOR membranes, while Nafion™ has a proton conductivity of approximately 0.1 S·cm−1. The increase in the proton conductivity upon sulfonation despite the decrease in water uptake was explained by the dominance of the Grotthuss mechanism over the vehicular mechanism for proton conductivity. Fuel cell test results showed that while SPVA‐MOR membranes cannot outperform Nafion™, they give higher power output than PVA‐MOR membranes, especially at low temperatures and high methanol concentrations. © 2017 Curtin University of Technology and John Wiley & Sons, Ltd.

Preparation and properties of crosslinked hybrid proton exchange membrane based on sulfonated poly (arylene ether nitrile) with improved selectivity for fuel cell application

Novel sulfonated poly (arylene ether nitrile) with pendant carboxylic group copolymers have been prepared as proton exchange membranes which were applied in direct methanol fuel cells (DMFCs). Compared with others, this work shows two main advantages: the crosslinked method is uncomplicated and the membranes were prepared via the hydroquinonesulfonic acid potassium salt (SHQ) as crosslinker mingled in sulfonated poly (arylene ether nitrile) (SPEN) to avoid the decrease of proton conductivity. The obtained crosslinked membranes exhibited improved dimensional stability; larger tensile strength than that of pure SPEN; and good thermal, mechanical properties. Furthermore, after crosslinking, the membranes had low methanol permeability values (0.78–3.4 × 10−7 cm2 s−1) and displayed good proton conductivities in the range of 0.0328–0.0385 S·cm−1 at room temperature. The sample of SPEN-SHQ-5 % showed highest selectivity value of 4.205 × 105 S·s cm−3, which was 11.9 times higher than that of Nafion 117. All of these results indicated that these membranes would be the potential candidates as proton exchange membranes (PEMs) in DMFCs.

Selectivity of Direct Methanol Fuel Cell Membranes.

Sulfonic acid-functionalized polymer electrolyte membranes alternative to Nafion® were developed. These were hydrocarbon systems, such as blend sulfonated polyetheretherketone (s-PEEK), new generation perfluorosulfonic acid (PFSA) systems, and composite zirconium phosphate–PFSA polymers. The membranes varied in terms of composition, equivalent weight, thickness, and filler and were investigated with regard to their methanol permeation characteristics and proton conductivity for application in direct methanol fuel cells. The behavior of the membrane electrode assemblies (MEA) was investigated in fuel cell with the aim to individuate a correlation between membrane characteristics and their performance in a direct methanol fuel cell (DMFC). The power density of the DMFC at 60 °C increased according to a square root-like function of the membrane selectivity. This was defined as the reciprocal of the product between area specific resistance and crossover. The power density achieved at 60 °C for the most promising s-PEEK-based membrane-electrode assembly (MEA) was higher than the benchmark Nafion® 115-based MEA (77 mW·cm−2 vs. 64 mW·cm−2). This result was due to a lower methanol crossover (47 mA·cm−2 equivalent current density for s-PEEK vs. 120 mA·cm−2 for Nafion® 115 at 60 °C as recorded at OCV with 2 M methanol) and a suitable area specific resistance (0.15 Ohm cm2 for s-PEEK vs. 0.22 Ohm cm2 for Nafion® 115).

Membranes from Blended Ionomer/PVDF Nanofibers: I. PFSA/PVDF and PFIA/PVDF Fiber Spinning and Membrane Fabrication

Blends and composites of various perfluoroionomers and uncharged polymers, e.g., poly(vinylidene fluoride) (PVDF), have been widely studied as the proton conducting membrane material for direct methanol and hydrogen/air fuel cells. The general idea of blending was to decouple the mechanical and swelling properties of a membrane from its proton conductivity. Thus, for a hydrogen/air fuel cell, the goal was to fabricate a membrane with low sheet resistance, low areal swelling, and good mechanical properties. For a direct methanol fuel cell membrane, blended were made to lower methanol crossover methanol while maintaining a high proton conductivity. In 2008, Pintauro and co-workers [1] showed how nanofiber electrospinning can be used to fabricate composite fuel cell membranes. The method was an alternative to traditional blending. These early membranes were made by electrospinning an ionomer fiber mat followed by the impregnation of an uncharged, reinforcing polymer into the inter-fiber voids; inverse structures where an uncharged polymer was electrospun and the voids were filled with an ionomer were also studied [2]. Dual-fiber electrospinning was introduced in 2011 by Ballengee and Pintauro [3] as a means to eliminate a separate interfiber void-filling impregnation step during nanofiber composite membrane fabrication. The ionomer and uncharged polymers were simultaneously electrospun as separate fibers that co-deposited as a well-mixed mat on the collector surface. Subsequent processing via hot-pressing, and either annealing or solvent vapor exposure, induced the flow of one of the polymer components into the interfiber void space while retaining the nanofiber morphology of the second polymer. Two distinct morphologies were produced from such dual fiber mats: (i) a network of ionomer nanofibers embedded in an uncharged reinforcing polymer matrix and (ii) an ionomer matrix reinforced by a network of uncharged nanofibers. Membranes were prepared via dual fiber electrospinning using various polymer combinations, including Nafion, Aquivion and 3M Company PFSA ionomers, and polyphenylsulfone, poly(vinylidene fluoride), and polyamide-imide as the uncharged components. We have recently developed a new electrospinning strategy for membrane preparation, were a solution of a binary polymer mixture is electrospun and then the single fiber mat is hot-pressed into a dense blended membrane. Here, we exploit the electrospinning process to insure blending of seemingly incompatible polymers (i.e., thorough mixing of the polymer components as the electrospinning solution emerges from the spinneret tip followed by rapid solvent evaporation and the “freezing in” of a blended morphology within a 100-500 nm diameter fiber. In this presentation the methods used to electrospin various single fibers blends of perfluoroionomers with KynarÒ HSV 900 PVDF will be presented, with a focus on NafionÒperflourosulfonic acid ionomer and low equivalent weight PFIA ionomer from 3M Company. Procedures for converting the nanofiber mats into dense and defect-free membranes will be described. Preliminary characterization results will be summarized (water swelling, proton conductivity, and mechanical properties) and contrasted with dual fiber membranes and/or conventional solution cast blended films. REFERENCES [1] J. Choi, K. M. Lee, R. Wycisk, P. N. Pintauro and P. T. Mather, Macromolecules, 41, 4569, 2008. [2] M. Gummalla, Z. Yang, P. Pintauro, K.M. Lee, R.Wycisk, US Patent Application, US 13/995,580, 2011 [3] J. B. Ballengee and P. N. Pintauro, Macromolecules , 44, 7307, 2011.

Functionalizing Biomaterials to Be an Efficient Proton-Exchange Membrane and Methanol Barrier for DMFCs

Biobased materials capable of transforming into selective proton-exchange composite membranes (PEMs) are highly favored for use in direct methanol fuel cells (DMFCs) because of their low cost and abundance. Here, a polysaccharide and a clay have been functionalized together to make a highly proton selective PEM. Use of chitosan and clay composites ensured limited methanol crossover and thereby high measured performance via efficient fuel convertibility. In this study, sulfonated natural nanocomposite PEMs made of chitosan and sodium–montmorillonite (CS-MMT) were characterized for their water swelling, proton conductivity and methanol permeability parameters. The CS-MMT membrane with a proton conductivity of 4.92 × 10–2 S cm–1 and a power density of 45 mW/cm2 showed a measured methanol crossover current density (J) of <100 mA/cm2. For higher methanol concentrations (4, 6 and 8 M), fuel loss was ∼4 times less in comparison with commercially successful PEMs, such as Nafion 117.

Performance of PVDF supported silica immobilized phosphotungstic acid membrane (Si-PWA/PVDF) in direct methanol fuel cell

PVDF supported silica-immobilized phosphotungstic acid membrane (Si-PWA/PVDF) was synthesized by impregnation of silica immobilized phosphotungstic acid particles in porous PVDF film. Pore size distribution as well as stability of membrane in oxidative environment was determined using Fenton's reagent test. Stability of membrane against leaching of PWA which provides ion exchanging capacity was also determined and found to be adequate. Properties which affect performance of membrane in DMFC like water uptake, methanol cross-over and proton conductivity were measured. Water uptake of the membrane increased from 30.3% to 37.9% as the temperature was increased from 25 °C to 80 °C. The proton conductivity of the membrane increased from 4.3 mS cm−1 to 20 mS cm−1 with increase in the temperature from 25 °C to 80 °C. Methanol uptake of the Si-PWA/PVDF membrane was low compared to Nafion membrane and changed by very small amount with increase in temperature. Effect of operating parameters on performance of direct methanol fuel cell (DMFC) with the synthesized Si-PWA/PVDF was determined. DMFC performance improved on increasing temperature. As the temperature was increased from 25 °C to 60 °C, open circuit voltage (OCV) increased from 0.685 V at 0.815 V and the peak power density increased from 21.4 mW cm−2 to 44.0 mW cm−2. Maximum peak power density was obtained with 1 M methanol concentration and 60% relative humidity. Peak power density decreased with further increase in both methanol concentration and relative humidity.

Methylated polybenzimidazole and its application as a blend component in covalently cross-linked anion-exchange membranes for DMFC

In the present work, the development and the characterization of new anion exchange membranes (AEMs) based on a methylated polybenzimidazole (mPBIOO) and their application in direct methanol fuel cell (DMFC) are described. For the preparation of methylated PBIOO (mPBIOO), a gentle methylation method was developed by using dimethyl carbonate (DMC) and 1,4-diazabicyclo[2.2.2]octane (DABCO). The synthesis of covalent cross-linked AEMs was achieved using the mPBIOO, sulfinated polysulfone (PPSU-SO2Li), DABCO and diiodobutane (DIB). The AEMs had IECs of more than 2.0meqg−1, which indicates a high concentration of anion-exchange groups. Depending on the cross-linking degree, the methanol gravimetric uptake reached a maximum of 43% (by mass) and all AEMs showed an excellent ex situ alkaline stability. After 10d in aqueous KOH (1M) at 90°C the IECs, ionic conductivities, and mechanical stabilities did not show a significant decrease. DMFC measurements show a performance improvement of a factor of three when the membranes were solvent (dimethylacetamide) extracted before integration into the fuel cell. With the usage of non-Pt catalysts, a maximum power density of 120mWcm−2 was achieved.

Keynote Presentation: Materials and Properties of Anionic Membranesfor Direct Methanol Fuel Cells

not Available.

Radiolytic Synthesis of Vinyl Polymer‐Clay Nanocomposite Membranes for Direct Methanol Fuel Cell

The three‐type vinyl polymer‐clay nanocomposite membranes with sulfonate (–SO3Na) are prepared by the solvent casting method after radiation‐induced copolymerization for application of the direct methanol fuel cell (DMFC) membrane. The three‐type vinyl polymers in polymer‐clay nanocomposite membranes are included in poly(styrene‐co‐sodium styrene sulfonate), poly(St‐co‐NaSS), poly(2‐hydroxyethyl methacrylate‐co‐NaSS), poly(HEMA‐co‐NaSS), and poly(acrylic acid‐co‐NaSS), and poly(AAc‐co‐NaSS). The proton conductivity (S/cm), water uptake (%), and ion‐exchange capacity (meq/g) of the poly(St‐co‐NaSS)‐clay nanocomposite membrane are 0.0779, 32.4, 3.63, respectively. The MeOH permeability of the poly(St‐co‐NaSS)‐clay nanocomposite membrane is exhibited as 7.7 × 10−9 mmol · cm−2 · s−1. DMFC performance for poly(St‐co‐NaSS)‐clay nanocomposite membrane is also measured in cell voltage and power density verses current density. As results, the poly(St‐co‐NaSS)‐clay nanocomposite membrane can be used as a DMFC membrane on behalf of the commercial Nafion membrane.

Improvement in direct methanol fuel cell performance by treating the anode at high anodic potential

This work investigates the effect of a high anodic potential treatment protocol on the performance of a direct methanol fuel cell (DMFC). DMFC membrane electrode assemblies (MEAs) with PtRu/C (Hi-spec 5000) anode catalyst are subjected to anodic treatment (AT) at 0.8 V vs. DHE using potentiostatic method. Despite causing a slight decrease in the electrochemical surface area (ECSA) of the anode, associated with ruthenium dissolution, AT results in significant improvement in DMFC performance in the ohmic and mass transfer regions and increases the maximum power density by ∼15%. Furthermore, AT improves the long-term DMFC stability by reducing the degradation of the anode catalyst. From XPS investigation, it is hypothesized that the improved performance of AT-treated MEAs is related to an improved interface between the catalyst and Nafion ionomer. Among potential explanations, this improvement may be caused by incorporation of the ionomer within the secondary pores of PtRu/C agglomerates, which generates a percolating network of ionomer between PtRu/C agglomerates in the catalyst layer. Furthermore, the decreased concentration of hydrophobic CF2 groups may help to enhance the hydrophilicity of the catalyst layer, thereby increasing the accessibility of methanol and resulting in better performance in the high current density region.

Degradation mechanisms and mitigation strategies of metal cations in recycled fuel for direct methanol fuel cell membrane electrode assembly

Some metal contaminants, such as Al3+, Ni+2, Fe2+ and Cr3+, are produced during reactions in heat exchangers, stacks, and other fuel/water management system components. Due to the gradual build-up of these contaminants generated in the system, direct methanol fuel cell (DMFC) membrane electrode assemblies (MEAs) deteriorate steadily with increasing operation time. Hence, this study systematically investigates the effects of metal cations by supplying various concentrations of metal solutions to the fuel stream at constant-current densities, with the aim of understanding the mechanism and influence of metal contamination on a DMFC MEA. Various electrochemical diagnostic techniques are used to determine the main cause of MEA degradation, including electrochemical impedance spectroscopy, electrode polarization, and methanol stripping voltammetry. In addition, the critical concentration of metal cations in methanol fuel is investigated for high DMFC MEA stability. Further, various novel methods for mitigating the influence of the metal contaminants on the performance of a DMFC are suggested and verified.

Sulfonated poly(ether ether ketone) membranes with sulfonated graphene oxide fillers for direct methanol fuel cells

Sulfonated organosilane functionalized graphene oxides (SSi-GO) synthesized through the grafting of graphene oxide (GO) with 3-mercaptopropyl trimethoxysilane and subsequent oxidation have been used as a filler in sulfonated poly(ether ether ketone) (SPEEK) membranes. The incorporation of SSi-GOs greatly increases the ion-exchange capacity (IEC), water uptake, and proton conductivity of the membrane. With well-controlled contents of SSi-GOs, the composite membranes exhibit higher proton conductivity and lower methanol permeability than Nafion® 112 and Nafion® 115, making them particularly attractive as proton exchange membranes (PEMs) for direct methanol fuel cells (DMFC). The composite membrane with optimal SSi-GOs content exhibit over 38 and 17% higher power densities, respectively, than Nafion® 112 and Nafion® 115 membranes in DMFCs, offering the possibilities to reduce the DMFC membrane cost significantly while keeping high-performance.

Development of polystyrene sulfonate/glycol chitosan hybrid membrane for direct methanol fuel cell

ABSTRACT The direct methanol fuel cell (DMFC) is the battery of the system, which directly supplies methanol to the cell containing a polyelectrolyte membrane. As for DMFC, a miniaturization and weight saving in the whole system are possible, because device does not have to constitute reformer. Therefore, DMFC is expected as a power source of a mobile device. Polyelectrolyte membranes for DMFC need a characteristic of the proton conductivity and the reduction of methanol crossover (MCO). In this research, hybrid membrane comprising a polystyrene sulfonate (PSS) and a glycol chitosan (G-Ch) was investigated. PSS/G-Ch hybrid membranes were prepared by cast method and were cross-linked with glutaraldehyde (GA) to reduce the water content. From the Attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) measurement, the amino group of the G-Ch origin and the sulfonate group of the PSS origin in hybrid membranes generated ionic bond. On the other hand, the proton conductivity of the hybr...

Effect of operating temperature on the behavior of promising SPEEK/cSMM electrolyte membrane for DMFCs

The behavior of sulfonated poly (ether ether ketone) (SPEEK) with different degrees of sulfonation (DS) (60–76%) blended with charged surface modifying macromolecule (cSMM) at different operating temperatures as an electrolyte membrane for direct methanol fuel cell (DMFC) application has been studied. A good DMFC electrolyte membrane should possess high proton conductivity and low methanol permeability. In this work, the fabricated SPEEK/cSMM membranes were compared with pure SPEEK and commercial Nafion 112 membranes in terms of water uptake, proton conductivity, and methanol permeability at temperature range of room to 80°C. The water uptake of SPEEK/cSMM membranes increased with the temperature and it was higher than that of SPEEK and Nafion 112 membranes; however newly fabricated membranes with 68% and 76% DS were dissolved at high temperatures although showed the same trend at lower temperatures. In agreement with the result of water uptake, proton conductivity of SPEEK/cSMM membranes also increased with temperature and was higher as compared to the corresponding SPEEK membranes; however it was still lower than that of Nafion 112. The methanol permeability values of the SPEEK/cSMM membranes were lower at different temperatures as compared to corresponding SPEEK and Nafion 112 at the same condition. Owing to considerable proton conductivity and lower methanol permeability values, SPEEK60/cSMM exhibited the highest overall performance than other tested membranes at 60°C. These results indicated that SPEEK60/cSMM membrane is promising to be used as a polymer electrolyte membrane in direct methanol fuel cell.

Nanocomposite membranes of Nafion and Fe3O4-anchored and Nafion-functionalized multiwalled carbon nanotubes exhibiting high proton conductivity and low methanol permeability for direct methanol fuel cells

Fe3O4 magnetic nanoparticle-anchored and Nafion-functionalized multiwalled carbon nanotubes (MWCNT–MNP–Nafion) have been prepared and used as a nano-additive for Nafion. The addition of 0.1 wt% of MWCNT–MNP–Nafion to Nafion results in the membranes showing a reduction of methanol permeability from 30.1 × 10−7 cm2 s−1 to 6.8 × 10−7 cm2 s−1 and an increase of proton conductivity from 31 mS cm−1 to 78 mS cm−1. The presence of MWCNT–MNP–Nafion reduces the ionic cluster sizes and decreases the free volume element concentration of the modified Nafion membrane. Both have been verified with small angle X-ray scattering spectroscopy and positron annihilation lifetime spectroscopy and contribute to the reduction of the methanol permeability of the membrane. The increase in the proton conductivity originates from the formation of proton-conducting pathways on the MWCNT bundles. For the membrane fabricated under a magnetic field, its proton conductivity further increases to 85 mS cm−1 due to the magnetically-driven alignment of MWCNT–MNP–Nafion in the Nafion matrix (A-Nafion-NM-0.1). Compared to the plain recast Nafion membrane, the A-Nafion-NM-0.1 membrane has a 15-fold membrane selectivity, an 8.7-fold maximum power density, and a 6.6-fold current density at an operating voltage of 0.4 V in the tests for direct methanol fuel cells (DMFC). The high performance of the membrane in the DMFC tests demonstrates that the MWCNT–MNP–Nafion is a highly efficient additive for the preparation of Nafion-based membranes for DMFCs.