Membranes For Direct Methanol Fuel Cells Research Articles

Isomeric effect of sulfonated poly(arylene ether)s comprising dihydroxynaphthalene on properties for polymer electrolyte membranes

AbstractPolymer electrolyte membranes (PEMs) made of sulfonated poly(arylene ether)s consisted of 3,3′‐disulfo‐4,4′‐dichlorodiphenylsulfone disodium salt, 2,6‐dichlorobenzonitrile, and one of three dihydroxynaphthalene isomers (2,6‐, 2,7‐, and 1,5‐dihydroxynaphthalene, abbreviated as 2,6‐N, 2,7‐N, and 1,5‐N, respectively) were prepared with similar level of inherent viscosity and ion exchange capacity, and structural effect of the catenation in dihydroxynaphthalene isomers on membrane properties was compared. In the case of membranes for PEM fuel cell application with relatively high ion exchange capacity around 2.1 mequiv/g, three copolymers showed almost the same proton conductivity; however, swelling in water increased with the following order: 1,5‐N < 2,6‐N < 2,7N. In the case of direct methanol fuel cell membranes with lower ion exchange capacity around 1.5 mequiv/g, no remarkable difference in proton conductivity was also observed in three isomeric copolymers and swelling property and methanol permeability were lower in 1,5‐N and 2,6‐N copolymers than 2,7‐N copolymer. These tendencies show that higher rigidity or energy barrier for conformational change of polymer chain gives better performance of PEM for fuel cells with superior dimensional stability. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Molecular modeling of the morphology and transport properties of two direct methanol fuel cell membranes: Phenylated sulfonated poly(ether ether ketone ketone) versus Nafion

Abstract

Multilayered sulphonated polysulfone/silica composite membranes for fuel cell applications

Polymer electrolyte membranes used in proton exchange membrane fuel cell (PEMFC) and direct methanol fuel cell (DMFC) suffer from low dimensional stability. Hence multilayered membranes using sulfonated polysulfone (SPSu) and silica (SiO2) were fabricated to alter such properties. The introduction of an SiO2 layer between two layers of SPSu to form the multilayered composite membrane enhanced its dimensional stability, but slightly lowered its proton conductivity when compared to the conventional SPSu/SiO2 composite membrane. Additionally, higher water absorption, lower methanol permeability and higher flame retardancy were also observed in this newly fabricated multilayered membrane. The performance evaluation of the 2wt% SiO2 loaded multilayered membrane in DMFC showed a maximum power density of 86.25mWcm−2, which was higher than that obtained for Nafion 117 membrane (52.8mWcm−2) in the same single cell test assembly. Hence, due to the enhanced dimensional stability, reduced methanol permeability and higher maximum power density, the SPSu/SiO2/SPSu multilayered membrane can be a viable and a promising candidate for use as an electrolyte membrane in DMFC applications, when compared to Nafion.

Sulfonated poly(arylene ether sulfone)/Laponite-SO 3H composite membrane for direct methanol fuel cell

Polymer nanocomposite membranes based on sulfonated poly(arylene ether sulfonate) (SPAES) containing a flake filler (Laponite) with varying degrees of sulfonation, were prepared and characterized for application in direct methanol fuel cells (DMFCs). Unlike most other clays, Laponite crystals are very small in size with a very low aspect ratio (diameter to thickness ratio) of 25–30. They improve the mechanical, thermal properties and decreased the fuel permeability. However, polymer composite membranes containing non-proton conducting inorganic particles tend to show low proton conductivity, as compared with pristine polymer membranes. To resolve this problem, prior to the preparation of the composite membranes, Laponite-Na+(NLa) was sulfonated with various amounts of organo silanes (3-Mercaptopropyl trimethoxysilane (SH-silane)) via an ion exchange method. Functionalized Laponite with the organic silane compound showed higher ion exchange capacity and ion conductivity, respectively. In order to minimize the loss of proton conductivity while reducing the methanol permeability, various amounts (0.5–2.0 wt%) of the organically sulfonated Laponite (SLa) were introduced into the SPAES matrices. The performances of hybrid membranes for DMFCs in terms of mechanical properties, behavior of water in membranes, proton conductivity and methanol permeability were investigated.

A novel membrane for DMFC – Na2Ti3O7 Nanotubes/Nafion® composite membrane: Performances studies

Systematic experiments have been carried out to study the performance of the novel sodium titanate (Na2Ti3O7) nanotube/Nafion® composite membrane (5 wt% Na2Ti3O7) in a single direct methanol fuel cell (DMFC) at different operating temperatures, methanol concentrations, air flow rates, methanol flow rates, and cathode humidification temperatures. The experimental results showed that the composite membrane outperform pure Nafion® membranes with the same thickness, Nafion®112, under all the operating conditions. Furthermore, under some operating conditions, the new composite membranes even outperform Nafion®117, a much thicker membrane. These experimental results have proved that the new composite membrane is superior to pure Nafion® membrane in DMFCs and the addition of Na2Ti3O7 nanotubes into Nafion® is an effective way to improve membrane performances.

Characterization of High-Temperature Proton-Exchange Membranes Based on Phosphotungstic Acid Functionalized Mesoporous Silica Nanocomposites for Fuel Cells

The synthesis and characteristics of high-temperature proton-exchange membranes based on mesoporous silica nanocomposite functionalized with phosphotungstic acid (HPW) were investigated in detail for applications in proton-exchange membrane fuel cells (PEMFCs) and direct methanol fuel cells (DMFCs). The HPW–meso-silica nanocomposites were characterized by small-angle X-ray scattering (SAXS), FTIR spectroscopy, Raman spectroscopy, TGA, N2 absorption isotherm, water uptake, TEM, conductivity, and fuel cell performance. The spectroscopy results indicate interactions between the Keggin anions of HPW and meso-silica and the possible formation of (≡SiOH2+)(H2PW12O40–) species. The results show that the proton conductivity of the HPW–meso-silica nanocomposites depends strongly on the content of HPW. The threshold for the proton conductivity of the nanocomposite is ∼10 wt %. The best proton conductivity is 0.07 S cm–1 at 25 °C under 100% relative humidity (RH) with an activation energy of ∼14 kJ mol–1, obtained on HPW–meso-silica nanocomposites with 67–83% HPW. A PEMFC based on a HPW–meso-silica membrane produced a power output of 308 mW cm–2 at 80 °C and 80% RH in H2/O2, 206 mW cm–2 at 80 °C and 80% RH in H2/air, and 134 mW cm–2 at 160 °C in methanol/air without external humidification. The high tolerance of HPW–meso-silica nanocomposites toward RH fluctuations demonstrates the unique high water retention capability of HPW–meso-silica nanocomposites. The results indicate that HPW–meso-silica forms a promising proton-exchange membrane for PEMFCs and DMFCs operating at high temperatures.

Performance test and degradation analysis of direct methanol fuel cell membrane electrode assembly during freeze/thaw cycles

Performance and degradation of direct methanol fuel cell (DMFC) membrane electrode assembly (MEA) are analyzed after repeated freeze/thaw cycles. Three different MEAs stored at −20°C for 8h with the anode side full of methanol solution are selected to test the effects of low temperatures on performance. After the cell heated to 60°C within 30min, they are inspected to determine the degradation mechanism. The resistance R obtained by the polarization curve is essential for identifying the main component affecting cell performance. The electrochemical impedance spectroscopy (EIS) technique is used to characterize the DMFC after freeze/thaw cycles. Thus, deterioration is assessed by measuring the high-frequency resistance (HFR) and the charge-transfer resistance (CTR). The electrochemical surface area (ECA) is employed to investigate not only the actual chemical degradation but also membrane status since sudden loss of ECA on the cathode side can result from a broken membrane. Moreover, a strategy is designed to simulate actual conditions that may prevent the membrane from being broken. A DMFC stack without any heating or heat-insulation devices shall avoid to be stored at subzero temperatures since the membrane will be useless due to frozen of methanol solution.

Polymer Electrolyte Membranes Based on Sulfoethylcellulose and Poly(vinyl Alcohol) for Direct Methanol Fuel Cells

We have investigated the solvent uptake, thermal stability, tensile strength, proton conductivity, and the methanol permeability coefficient (PM) in aqueous methanol solutions for cross-linked sulfoethylcellulose/poly(vinyl alcohol) blend membrane (CL-SEC/PVA) and have investigated its applicability to direct methanol fuel cells (DMFC). CL-SEC/PVA membrane exhibits a proton conductivity of 0.017 S cm-1 at 25 ºC. CL-SEC/PVA membrane also shows low methanol permeability in methanol aqueous solutions. The membrane electrode assembly has been prepared by applying Nafion® as a binder in the catalyst layer. Performance of DMFC was estimated with different methanol concentrations. The open-circuit voltage is decreased with increasing the methanol concentration. CL-SEC/PVA membrane achieves the highest power density of 13mW cm-2 with 5M methanol solution at 25 ºC. The results suggest that CL-SEC/PVA membrane is potentially applicable to polymer electrolyte membranes for DMFC utilizing a high concentration methanol solution as a fuel.

Nano-sized Fe 2O 3–SO 42− solid superacid composite Nafion ® membranes for direct methanol fuel cells

In this paper, Fe 2O 3–SO 4 2−/Nafion ® composite membranes were prepared by a solution casting method. The physico-chemical properties of composite membranes were characterized by X-ray diffraction (XRD), SEM–EDX and thermogravimetric analysis (TGA). The water uptake ability, proton conductivity, and methanol permeability of the composite membranes were evaluated and compared with the recast Nafion ® membrane. The results showed that the proton conductivity and the water uptake of the composite membranes were slightly higher than that of the recast Nafion ® membrane. The composite membrane containing 5 wt.% Fe 2O 3–SO 4 2- showed superior ability to suppress methanol crossover, and it further improved the direct methanol fuel cell (DMFC) performances with both 1 M and 5 M methanol feeding, compared with the recast Nafion ® membrane. The preliminary 30 h lifetime test of the DMFC with the composite membrane with 5% Fe 2O 3–SO 4 2 − indicated that the composite membrane is stable working at the real DMFC operating conditions at least during the test. These results suggest the applicability of the composite membranes in DMFCs.

Effect of silane hydrophilicity on membrane transport properties of in-situ hybrid Nafion/organically modified silicate proton conductors for DMFC applications

In order to build a better understanding of in-situ hybrid Nafion/ORMOSIL (Organically MOdified SILicates) membranes for DMFC (direct methanol fuel cells) applications, we investigate the effect of silane hydrophilicity on membrane transport properties of the hybrid proton conductors in terms of water-channel structure and state of water. The following three contrast silanes are introduced in the decreasing order of hydrophilicity: tetraethoxy silane (TEOS), methyl triethoxy silane (MTES), and diethoxy dimethyl silane (DEDMS). To focus exclusively on the silane hydrophilicity, a pre-requisite condition assuring that the same concentration of silanes should be immersed into Nafion115 is fulfilled by examining the silane diffusion behavior. As the silane hydrophilicity increases, the water-channel size and water uptake of the hybrid membranes become larger but the number of freezable water molecules decreases. Meanwhile, the hybrid membranes prepared from the hydrophobic silanes show the higher proton conductivity, leading to the superior selectivity. This interesting transport behavior is explained by considering the morphological change and state of water in the hybrid membranes.

Preparation and properties of hybrid direct methanol fuel cell membranes by embedding organophosphorylated titania submicrospheres into a chitosan polymer matrix

Organophosphorylated titania submicrospheres (OPTi) are prepared and incorporated into a chitosan (CS) matrix to fabricate hybrid membranes with enhanced methanol resistance and proton conductivity for application in direct methanol fuel cells (DMFC). The pristine monodispersed titania submicrospheres (TiO 2) of controllable particle size are synthesized through a modified sol–gel method and then phosphorylated by amino trimethylene phosphonic acid (ATMP) via chemical adsorption, which is confirmed by XPS, FTIR and TGA. The morphology and thermal property of the hybrid membranes are explored by SEM and TGA. The ionic cross-linking between the –PO 3H 2 groups on OPTi and the –NH 2 groups on CS lead to better compatibility between the inorganic fillers and the polymer matrix, as well as a decreased fractional free volume ( FFV), which is verified by positron annihilation lifetime spectroscopy (PALS). The effects of particle size and content on the methanol permeability, proton conductivity, swelling and FFV of the membranes are investigated. Compared to pure CS membrane, the hybrid membranes exhibit an increased proton conductivity to an acceptable level of 0.01 S cm −1 for DMFC application and a reduced methanol permeability of 5 × 10 −7 cm 2 s −1 at a 2 M methanol feed.

Simultaneous Measurement of Proton Conductivity and Methanol Permeability for the Development of Direct Methanol Fuel Cell Membranes

DMFC membrane development is complicated by the fact that the two most important transport properties, methanol crossover and proton conductivity, are coupled, thus strategies that improve one property will almost invariably have an undesirable effect upon the other. Each measurement is usually done in separate experiments, even under different conditions. These measurements can be carried out in fuel cells and are indeed simultaneous, however, many complicating factors can interfere with the derived properties. This paper presents a methodology for the simultaneous measurement of membrane conductivity and methanol permeability. The equipment and method will be presented, and examples discussed including a comparison to analogous in-fuel cell results as well as examination of a series of experimental DMFC membranes. Further, a graphical means of viewing transport results as well as the derived benefits in rapid analysis and comparison of candidate membranes will be presented.

Simultaneously enhanced methanol barrier and proton conductive properties of phosphorylated titanate nanotubes embedded nanocomposite membranes

The current study aims at simultaneously enhancing the methanol barrier and proton conductive properties of membranes for direct methanol fuel cell (DMFC) by embedding phosphorylated titanate nanotubes (PTNTs) into chitosan (CS) membrane. The enhancement is most probably due to the intrinsic interfacial interactions between PTNTs and CS chains, which are verified by the increased thermal stability and homogeneous dispersion of the fillers. The influence of PTNTs incorporation conditions including acid concentration and filler content upon the resulting nanocomposite membrane performance is extensively investigated. Compared with plain CS membrane, the presence of PTNTs within chitosan matrix will lead to denser chain packing, thus reduce free volume cavity size and fractional free volume ( FFV) according to positron annihilation lifetime spectroscopy analysis. The reduced FFV and more tortuous pathway significantly suppress the methanol crossover through the membranes. Meanwhile, the presence of PTNTs constructs an uninterrupted channel for proton migration via functionalized P–OH groups and adsorbed water, and therefore improving the proton conductivity substantially. As a result, the nanocomposite membranes exhibit desirable comprehensive performance, which is about ten times higher than that of Nafion 117. We envisage that the current observations hint the encouraging application promises of such nanocomposite membranes in DMFC.

Radiation-grafted membranes based on polyethylene for direct methanol fuel cells

Styrene was grafted onto ultrahigh molecular weight polyethylene powder (UHMWPE) by gamma irradiation using a 60Co source. Compression moulded films of selected pre-irradiated styrene-grafted ultrahigh molecular weight polyethylene (UHMWPE-g-PS) were post-sulfonated to the sulfonic acid derivative (UHMWPE-g-PSSA) for use as proton exchange membranes (PEMs). The sulfonation was confirmed by X-ray photoelectron spectroscopy (XPS). The melting and flow properties of UHMWPE and UHMWPE-g-PS are conducive to forming homogeneous pore-free membranes. Both the ion conductivity and methanol permeability coefficient increased with degree of grafting, but the grafted membranes showed comparable or higher ion conductivity and lower methanol permeability than Nafion ® 117 membrane. One UHMWPE-g-PS membrane was fabricated into a membrane–electrode assembly (MEA) and tested as a single cell direct methanol fuel cell (DMFC). Low membrane cost and acceptable fuel cell performance indicate that UHMWPE-g-PSSA membranes could offer an alternative approach to perfluorosulfonic acid-type membranes for DMFC.

Simultaneous Measurement of Proton Conductivity and Methanol Permeability for the Development of Direct Methanol Fuel Cell Membranes

not Available.

Nanoscale Phase Separation of Sulfonated Poly(arylene ether sulfone)/Poly(ether sulfone) Semi-IPNs for DMFC Membrane Applications

Unprecedented improvement in the selectivity (the ratio of proton conductivity to methanol permeability) of DMFC (direct methanol fuel cell) membranes has been demonstrated with a value roughly 16 times higher than that of Nafion117 having been achieved. The novel morphology of semi-interpenetrating polymer network (semi-IPN) membranes characterized by nanometer-sized domains as well as well-developed phase cocontinuity is a key factor in enabling such notable progress, which has not been seen in conventional microscale phase separation. The semi-IPN membranes (sIPN-100) consisted of a hydrophilic component acting as a proton conductor, that is, acrylate-terminated fully sulfonated poly(arylene ether sulfone) oligomers (acSPAES-100, degree of sulfonation = 100%), and a hydrophobic component functioning as a methanol barrier, that is, poly(ether sulfone) copolymers (RH-2000). We determined the nanoscale phase separation of sIPN-100 by deliberately controlling the kinetics (the change of solvent-evaporation...

The Effect of Proton Conductivity of SPEEK Composite Membrane with Organic Compounds for DMFC

Direct methanol fuel cells(DMFCs) are receiving significant attention in the portable power source and electric vehicular transportation because of its high energy efficiency as liquid fuel, low cost, and no requirement of fuel reforming process. In this study, we synthesized the Sulfonated poly(ether ether ketone) (SPEEK) to evaluate the possibility of use as a proton exchange membrane for DMFC. And poly(vinylidienedifluoride) (PVDF) was used to increase proton conductivity in SPEEK and simultaneously to prevent methanol transport through the cross linked membrane. Furthermore, in order to improve the electrical composite properties for DMFC applications.

Nafion ®/H-ZSM-5 composite membranes with superior performance for direct methanol fuel cells

Solution cast composite direct methanol fuel cell membranes (DEZ) based on DE2020 Nafion ® dispersion and in-house prepared H-ZSM-5 zeolites with different Si/Al ratios were prepared and thoroughly characterized for direct methanol fuel cell (DMFC) applications. All composite membranes have indeed lower methanol permeability and higher proton conductivity than pure DE2020 membrane. The composite membranes with Si/Al ratio 25 and 5 wt.% of zeolites (DEZ25-5) having the lowest methanol permeability and the membrane with Si/Al ratio 50 and 1 wt.% of zeolites (DEZ50-1) having the highest proton conductivity were tested in the DMFC for several days. The DEZ25-5 has the best performance; namely high power density and stable performance in time.

A facile surface modification of Nafion membrane by the formation of self-polymerized dopamine nano-layer to enhance the methanol barrier property

Abstract By immersing Nafion membrane into dopamine aqueous solution under mild conditions, a series of modified Nafion membranes for the application in direct methanol fuel cell (DMFC) were fabricated. High resolution scanning electron microscope and Fourier transform infrared spectra characterization revealed that a dense nano-layer around 50 nm was formed and adhered tightly to Nafion surface. Small-angle X-ray scattering, wide X-ray diffractometer and positron annihilation lifetime spectroscopy analysis implied that the microstructure such as phase-separated structure and ion-cluster channel of Nafion layer was slightly changed after surface modification. The influence of modification conditions including pH value, dopamine concentration and immersing time upon membrane performance was investigated. Due to the effective reduction of methanol dissolution and enhancement of methanol diffusion resistance, the methanol crossover of the modified membranes was dramatically suppressed by about 79% from 3.14 × 10−6 to about 0.65 × 10−6 cm2 s−1. Meanwhile, the proton conductivity of the modified membranes was slightly decreased to be around 0.06 S cm−1. Consequently, the comprehensive performance of the modified membranes was improved by about five times. These results hinted the application promises of such modified Nafion membranes in DMFC.

Restructure proton conducting channels by embedding starburst POSS-g-acrylonitrile oligomer in sulfonic perfluoro polymer matrix

Unique starburst nanoparticles are synthesized via grafting polyacrylonitrile short chains to the cubic polyhedral oligomeric silsesquioxane (POSS) by atom transfer radical polymerization (ATRP). Introduction of these branched nanoparticles ( sb-POSS) into the sulfonic perfluoro polymer (SPFP, e.g. Nafion ®) matrix in appropriate contents gives significant improvements in the performance of SPFP membranes as direct methanol fuel cell (DMFC). This enhancement is associated with the initial clustering of sb-POSS particles in the SPFP matrix when the sb-POSS content reaches to 5 wt.%. It has been found, from the differential scanning calorimetry (DSC) observation, that the SPFP molecules wage dual interactions on the sb-POSS particles, namely the hydrophobic perfluoro polymer chains of SPFP repel sb-POSS particles while the hydrophilic moieties associate with them. The content of sb-POSS strongly affects the assembly of hydrophilic channels in the membrane and, therefore, the membrane performance in a single direct methanol fuel cell (DMFC). The sb-POSS (5 wt.%)-SPFP composite membrane manifests an increase of 122% in power output of DMFC at 80 °C. In brief, this work offers a new insight into how the unique interactions between soft nanoparticles and amphiphilic polymer chains affects performances of proton exchange membranes (PEMs) in DMFC.