Fabrication of MEA with hydrocarbon based membranes using low temperature decal method for DMFC

The membrane electrode assembly (MEA) with hydrocarbon (HC) based membranes made by a low temperature decal method has been investigated for the direct methanol fuel cells (DMFCs). The conventional low temperature decal (LTD) transfer method (comprised of three layers; viz., carbon, Nafion bonded electrodes and outer ionomer layers over the decal Teflon substrates) meant for the MEAs made of Nafion type membranes is suitably modified to use with hydrocarbon (HC) based membranes. The modification of conventional LTD method is effected by means of modulating the three-layered structure and optimizing other parameters to facilitate complete transfer of catalyst layers onto the HC membranes. The MEAs prepared by the modified LTD method have yielded 21 % higher DMFC performance compared to that of the MEAs produced by conventional LTD method. The structure and electrochemical properties of the MEAs have been analyzed by the field-emission scanning electron microscopy (FE-SEM) and the electrochemical impedance spectroscopy (EIS).     

Long-term durability test for direct methanol fuel cell made of hydrocarbon membrane

A long-term durability test has been conducted for a direct methanol fuel cell (DMFC) using the commercial hydrocarbon membrane and Nafion ionomer bonded electrodes for 500 h. Membrane electrode assembly (MEA) made by a decal method has experienced a performance degradation about 34% after 500 h operation. Cross-sectional analysis of the MEA shows that the poor interfacial contact between the catalyst layers and membrane in the MEA has further deteriorated after the durability test. Therefore, the internal resistance of a cell measured by electrochemical impedance spectroscopy (EIS) has considerably increased. The delamination at the interfaces is mainly attributed to incompatibility between polymeric materials used in the MEA. Furthermore, X-ray diffraction (XRD) analysis reveals that the catalyst particles have grown; thereby decreasing the electrochemical surface area. Electron probe micro analysis (EPMA) shows a small amount of Ru crossover from anode to cathode; and its effect on the performance degradation has been analyzed.     

Direct methanol fuel cell (DMFC) based on PVA/MMT composite polymer membranes

A novel composite polymer electrolyte membrane composed of a PVA polymer host and montmorillonite (MMT) ceramic fillers (2–20 wt.%), was prepared by a solution casting method. The characteristic properties of the PVA/MMT composite polymer membrane were investigated using thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), scanning electron microscopy (SEM), and micro-Raman spectroscopy, and the AC impedance method. The PVA/MMT composite polymer membrane showed good thermal and mechanical properties and high ionic conductivity. The highest ionic conductivity of the PVA/10 wt.%MMT composite polymer membrane was 0.0368 S cm⁻¹ at 30 °C. The methanol permeability (P) values were 3–4 × 10⁻⁶ cm² s⁻¹, which was lower than that of Nafion 117 membrane of 5.8 × 10⁻⁶ cm² s⁻¹. It was revealed that the addition of MMT fillers into the PVA matrix could markedly improve the electrochemical properties of the PVA/MMT composite membranes; which can be accomplished by a simple blend method. The maximum peak power density of the DMFC with the PtRu anode based on Ti-mesh in a 2 M H₂SO₄ + 2 M CH₃OH solution was 6.77 mW cm⁻² at ambient pressure and temperature. As a result, the PVA/MMT composite polymer appears to be a good candidate for the DMFC applications.     

Composite polymer electrolyte membranes containing polyrotaxanes

Cast Nafion and sulfonated poly[styrene-b-(ethylene-r-butylene)-b-styrene] copolymer (sSEBS)-based composite membranes containing different amounts of organic nanorod-shaped polyrotaxane (PR) were prepared and characterized, with the aim of improving the methanol barrier property of polymer electrolyte membranes (PEMs) for application in direct methanol fuel cells (DMFCs). PR was prepared using the inclusion complex reaction between α-cyclodextrin (α-CD) and poly(ethylene glycol) (PEG) of different molecular weights. The addition of PR to the structure of sSEBS, which involves hexagonal packing of cylinders, reduces the proton conductivity, as well as the methanol permeability, implying the creation of a tortuous path for methanol. The addition of PR to Nafion with ionic clusters reduced the crystallinity. The conductivity of the Nafion composite membranes increased on PR addition and decreased at higher PR contents. The organic PR inside the membrane changed the morphology during membrane preparation and provided a tortuous path for the transport of methanol. All of the sSEBS- and Nafion-based PR composite membranes showed higher selectivity parameter.     

Synthesis and characterization of proton exchange membranes based on sulfonated poly(fluorenyl ether nitrile oxynaphthalate) for direct methanol fuel cells

A series of sulfonated poly(fluorenyl ether nitrile oxynaphthalate) (SPFENO) copolymers with different degree of sulfonation (DS) are synthesized via nucleophilic polycondensation reactions with commercially available monomers. Incorporation of the naphthalanesulfonate group into the copolymers and their copolymer structures are confirmed by ¹H NMR spectroscopy. Thermal stability, mechanical properties, water uptake, swelling behavior, proton conductivity and methanol permeability of the SPFENO membranes are investigated with respect to their structures. The electrochemical performance of a direct methanol fuel cell (DMFC) assembled with the SPFENO membrane was evaluated and compared to a DMFC with a Nafion 117 membrane. The DMFC assembled with the SPFENO membrane of proper DS exhibits better electrochemical performance compared to the Nafion 117-based cell.     

Covalent organic/inorganic hybrid proton-conductive membrane with semi-interpenetrating polymer network: Preparation and characterizations

A series of new covalent organic/inorganic hybrid proton-conductive membranes, each with a semi-interpenetrating polymer network (semi-IPN), for direct methanol fuel cell (DMFC) applications is prepared through the following sequence: (i) copolymerization of impregnated styrene (St), p-vinylbenzyl chloride (VBC) and divinylbenzene (DVB) within a supporting polyvinyl chloride (PVC) film; (ii) reaction of the chloromethyl group with 3-(methylamine)propyl-trimethoxysilane (MAPTMS); (ii) a sol–gel process under acidic conditions; (iv) a sulfonation reaction. The developed membranes are characterized in terms of Fourier transform infrared/attenuated total reflectance (FTIR/ATR), scanning electron microscopy/energy-dispersive X-ray analysis (SEM/EDXA), elemental analysis (EA) and thermogravimetric analysis (TGA), which confirm the formation of the target membranes. The developed copolymer chains are interpenetrating with the PVC matrix to form the semi-IPN structure, and the inorganic silica is covalently bound to the copolymers. These features provide the membranes with high mechanical strength. The effect of silica content is investigated. As the silica content increases, proton conductivity and water content decrease, whereas oxidative stability is improved. In particular, methanol permeability and methanol uptake are reduced largely by the silica. The ratio of proton conductivity to methanol permeability for the hybrid membranes is higher than that of Nafion 117. All these properties make the hybrid membranes a potential candidate for DMFC applications.     

A flexible direct methanol micro-fuel cell based on a metalized, photosensitive polymer film

This paper presents and investigates a concept for a flexible direct methanol micro-fuel cell (FDMMFC) based on the microstructuring of a Cr/Au metalized, thin polymer film of photosensitive SU-8. The inscribed microchannels in the electrodes are 200 μm × 200 μm in crosssection and spanning an active fuel cell area of 10 mm × 10 mm with a Pt-black catalyst on the cathode side of the membrane electrode assembly (MEA) and a Pt-Ru alloy catalyst on the anode side. Subsequently, the paper focuses on a thorough electrical characterization of the FDMMFC, under the employment of a variable resistor simulating an electrical load as well as a classical galvanostatical measurement technique. The fuel cell is also tested while operating in a bent, non-flat configuration. An extensive parameter study revealed an optimal and long-term stable operating condition for the fuel cell employing for both electrodes a serpentine flow field and a volume flow rate of 0.14 ml min⁻¹ of a 1 M methanol solution at the anode side with a gas volume flow rate of 8 ml min⁻¹ of humidified O₂ at the cathode side yielding a power density of 19.0 mW cm² at 75 mA cm² at a temperature of 60 °C.Furthermore, a flow-visualization of the two-phase flow occurring at the anode side has been performed by utilizing fluorescence microscopy. The strong influence of the two-phase flow on the performance of a fuel cell at high current densities becomes apparent in correlating the observed flow patterns with the corresponding current density of the polarization curve. The paper also investigates the functionality of the present FDMMFC under different bent conditions. The tests showed an insignificant drop of the electrical performance under bending due to an inhomogeneous contact resistance.     

Nafion-impregnated electrospun polyvinylidene fluoride composite membranes for direct methanol fuel cells

Composite membranes consisting of polyvinylidene fluoride (PVdF) and Nafion have been prepared by impregnating various amounts of Nafion (0.3–0.5 g) into the pores of electrospun PVdF (5 cm × 5 cm) and characterized by scanning electron microscopy, differential scanning calorimetry, X-ray diffraction, and proton conductivity measurements. The characterization data suggest that the unique three-dimensional network structure of the electrospun PVdF membrane with fully interconnected fibers is maintained in the composite membranes, offering adequate mechanical properties. Although the composite membranes exhibit lower proton conductivity than Nafion 115, the composite membrane with 0.4 g Nafion exhibits better performance than Nafion 115 in direct methanol fuel cell (DMFC) due to smaller thickness and suppressed methanol crossover from the anode to the cathode through the membrane. With the composite membranes, the cell performance increases on going from 0.3 to 0.4 g Nafion and then decreases on going to 0.5 g Nafion due to the changes in proton conductivity.     

Synthesis and properties of novel proton exchange membranes based on sulfonated polyethersulfone and N-phthaloyl chitosan blends for DMFC applications

Chitosan is modified by phthaloylation using an excess of phthalic anhydride at 130 °C and blended with the sulfonated polyethersulfone (SPES) to produce composite blend membranes. In particular the introduction of the phthaloyl group into the chitosan matrix increases its solubility in organic solvent, film formability, flexibility, low methanol permeability and with suitable ion conductivity. SPES and N-phthaloyl chitosan (NPHCs) blend membranes with various compositions were prepared and detailed investigation on water uptake, proton conductivity and methanol permeability has been conducted for its suitability in fuel cell environments. Methanol permeability studies envisaged that NPHCs blend membranes are impervious to methanol. The thermograms display the good thermal stabilities of blend membranes than Nafion-117. Relatively high selectivity parameter values of these membranes indicated their greater advantages over Nafion-117 membrane for targeting on fuel cell applications, especially in direct methanol fuel cell (DMFC) environments.     

Progress in poly(phenylene oxide) based cation exchange membranes for fuel cells and redox flow batteries applications

In fuel cell technologies, low-temperature proton exchange membrane fuel cells (LT-PEMFC), high-temperature proton exchange membrane fuel cells (HT- PEMFC), and direct methanol fuel cells (DMFC) are gained significant attention as a promising energy system for practical applications. The developments of cost-effective membrane materials with excellent physicochemical properties are indispensable for replacing the high cost of commercial membranes and achieving the higher performance of fuel cell systems. This review focuses on the developments and modifications of cost-effective poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) as a cation exchange membrane for LT-PEMFC, HT- PEMFC and DMFC. Notably, this review bridges the understanding of PPO based membranes, current advancements, structure, physicochemical properties and fuel cell performances. Progressive developments and a systematic overview of PPO-based membrane developments are explained in detail in terms of functionalization, blend, composite, acid-base, cross-linking, copolymerization, coated and reinforcement. Moreover, the changes in physicochemical properties and fuel cell performances in the membrane are deeply reviewed. Additionally, the utilization of PPO based membranes in different kinds of redox flow battery systems are reviewed. Overall, this review provides an exclusive vision and perspectives to develop the PPO based advanced, cost-effective, and high-performance membranes for fuel cell technologies and redox flow battery systems.     

Incorporating graphene oxide to improve the performance of Nafion-mordenite composite membranes for a direct methanol fuel cell

The proton exchange membrane is one of the critical parts of a direct methanol fuel cell. High proton conductivity and low methanol permeability are required. To enhance the performance of a direct methanol fuel cell, graphene oxide was incorporated to Nafion-mordenite composite membranes to enhance the compatibility and to decrease methanol permeability. It was found that the membrane with silane grafted on graphene oxide-treated mordenite with a graphene oxide content of 0.05% presented the highest proton conductivity (0.0560 S·cm⁻¹, 0.0738 S·cm⁻¹ and 0.08645 S·cm⁻¹ at 30, 50, and 70 °C, respectively). This was about 1.6-fold of the recast Nafion and commercial Nafion 117 and was about 1.5-fold of that without graphene oxide incorporation. Finally, the operating condition was optimized using response surface methodology and the maximum power density was investigated. Power density of about 4-fold higher than that of Nafion 117 was obtained in this work at 1.84 M and 72 °C with a %Error between the model prediction and the fuel cell experiment of 0.082%.     

Synthesis and characterization of anion exchange membranes for alkaline direct methanol fuel cells

Alkaline fuel cells suggest solution for the problems of low methanol oxidation kinetics and methanol crossover, which are limiting the development of direct methanol fuel cells. In this work, a novel anion exchange membrane, quaternized poly(aryl ether oxadiazole), was prepared through polycondensation, grafting and quaternization. The ionic conductivity of as-synthesized anion exchange membrane can reach up to 2.79 × 10⁻² S/cm at 70 °C. The physical and chemical stability of the anion exchange membranes could also meet the requirement for alkaline direct methanol fuel cells.     

Nafion nanocomposite membranes: Effect of fluorosurfactants on hydrophobic silica nanoparticle dispersion and direct methanol fuel cell performance

Nafion^®–silica nanocomposite membranes are successfully prepared by adding hydrophobic silica nanoparticles to a Nafion^® solution. To distribute these nanoparticles evenly in the Nafion^® matrix, various fluorosurfactants of different ionic character are employed. Fluorosurfactants with acid groups such as phosphonic acid and sulfonic acid play an important role in simultaneously increasing the homogeneous dispersion of silica nanoparticles, enhancing proton conductivity, and reducing the methanol permeability of the nanocomposite membranes. Therefore, the dispersion properties of inorganic fillers such as silica can significantly affect nanocomposite performance in direct methanol fuel cell (DMFC) applications, whereas surfactants, if used properly, can improve the nanocomposite membrane properties. In particular, a commercial fluorosurfactant containing a sulfonic acid group (Zonyl^® TBS) at the end of the surfactant chain exhibits better miscibility with the Nafion^® ionomer. This feature results in a reduction in the dimensional change of the nanocomposite membrane due to relatively lower water swelling and significantly reduced methanol permeability through the membrane. A membrane–electrode assembly (MEA) prepared from a Nafion^®–silica nanocomposite membrane with TBS shows the highest DMFC performance in terms of voltage vs. current density (V–I) and power density vs. current density (P–I). The current densities at 0.4 V and 90 °C are 342, 508, and 538 mA cm⁻² with 1, 3 and 5 M methanol being fed at the anode side, respectively.     

Efficient electrocatalysts for the oxygen reduction reaction,based on mixed carbonyl-phosphine clusters of iridium

This work reports the synthesis and characterization of two novel electrocatalysts for the oxygen reduction reaction based on iridium clusters containing carbonyl (CO) and phosphine (PPh₃ or PPh(OMe)₂) ligands. The study of the complexes by FTIR, XRD, EDS, XPS, MS, as well as ¹H, ¹³C and ³¹P NMR shows that they preserve the nuclearity of the iridium cluster used as precursor (Ir₄(CO)₁₂), while several of the carbonyl groups were substituted by the corresponding phosphine-type ligands and solvent (o-dichlorobenzene) molecules. The electrochemical characterization by rotating disk electrode measurements in an acid medium (0.5 mol L^?1 H₂SO₄), from which the kinetic parameters could be obtained, indicates that both clusters exhibit an important catalytic activity for the oxygen electroreduction, even in the presence of methanol in concentrations as high as 2.0 mol L^?1. According to these results, the new electrocatalysts are good potential candidates to be evaluated as cathodes in PEMFCs and DMFCs.     

Polybenzimidazole/zwitterion-coated polyamidoamine dendrimer composite membranes for direct methanol fuel cell applications

The zwitterion-coated polyamidoamine (ZC-PAMAM) dendrimer with ammonium and sulfonic acid groups has been synthesized and used as filler for the preparation of PBI-based composite membranes for direct methanol fuel cells. Polybenzimidazole (PBI)/ZC-PAMAM dendrimer composite membranes were prepared by casting a solution of PBI and ZC-PAMAM dendrimer, and then evaporating the solvent. The presence of ZC-PAMAM dendrimer was confirmed by FT-IR and energy-dispersive X-ray spectroscopy (EDS) mapping of sulfur and oxygen elements. The water uptake, swelling degree, proton conductivity, and methanol permeability of the membranes increased with the ZC-PAMAM dendrimer content. For the PBI/ZC-PAMAM-20 membrane with 20 wt% of ZC-PAMAM, it shows a proton conductivity of 1.83 × 10⁻² S/cm at 80 °C and a methanol permeability of 5.23 × 10⁻⁸ cm² s⁻¹. Consequently, the PBI/ZC-PAMAM-20 demonstrates a maximum power density of 26.64 mW cm⁻² in a single cell test, which was about 2-fold higher than Nafion-117 membrane under the same conditions.     

Controllable sulfonation of aromatic poly(arylene ether ketone)s containing different pendant phenyl rings

The sulfonation selectivity of various pendant phenyl groups in poly(arylene ether ketone) (Ph-3F-PAEK) is invested via the postsulfonation approach. The sulfonated Ph-3F-PAEKs with different degrees of sulfonation (DS) are quantitatively synthesized by controlling the length of the segments that cannot be sulfonated. In this study, ¹H NMR and FT-IR are used to confirmed the structures of the polymers and the experimentally DS values were calculated by ¹H NMR. The experimentally observed DSs are corresponding to the theoretical values expected from the monomer ratios. All the sulfonated membranes have excellent mechanical properties (with a Young's modulus >1.3 GPa, a tensile strength >55 MPa and the elongation >10%). Thermogravimetric analysis (TGA) is used to characterized the thermal stability of these polymers, and all the polymers show excellent thermal properties at high temperatures. The methanol permeability values of Ph-3F-SPAEKs in the range of 0.37 × 10⁻⁷ cm² s⁻¹ to 4.12 × 10⁻⁷ cm² s⁻¹ are much lower than that of Nafion^® 117 (1.55 × 10⁻⁶ cm² s⁻¹). It should be noted that the polymer with highest DS, Ph-3F-SPAEK-100 with an ion exchange capacity of 2.16 mequiv. g⁻¹, exhibits high proton conductivity of 0.187 S cm⁻¹ at 80 °C, which is also higher than that of Nafion^® 117.     

Terminally-crosslinked poly(ether sulfone) block copolymer,as a highly selective and stable polymer electrolyte membrane for DMFC applications

The terminally-crosslinked sulfonated poly(ether sulfone) block copolymer (SPES-b) was developed for use as a proton exchange membrane in DMFC applications. The properties of the membrane prepared from SPES-b were compared with those of its non-crosslinked counterpart (SPES-bn) and Nafion^®-117. The membrane displayed a well-defined morphology due to phase separation between the hydrophobic and hydrophilic ionic units in the SPES-b block copolymer. The terminally-crosslinked SPES-b membrane yielded a high proton conductivity of 0.09 S/cm and a low methanol permeability of 5.3 × 10⁻⁸ cm²/s at 20 °C, and the membrane displayed excellent dimensional, mechanical, hydrolytic, and oxidative stabilities.     

Performance of passive direct methanol fuel cell with poly(vinyl alcohol)-based polymer electrolyte membranes

Polymer electrolyte membranes (PEMs) were prepared from poly(vinyl alcohol) (PVA) and a modified PVA polyanion containing 2 mol% of 2-methyl-1-propanesulfonic acid (AMPS) groups as a copolymer. The effect of the AMPS content and the crosslinking conditions on the properties of the membranes was investigated in PEMs with various AMPS contents prepared under various crosslinking conditions. The proton conductivity and the permeability of methanol through the PEMs increased with increasing AMPS content, C_AMPS, and with decreasing annealing temperature, T_a, because of the increase in the degree of swelling. The permeability coefficient of methanol through the PEM prepared under the conditions of C_AMPS = 2.0 mol% and T_a 190 °C was approximately 30 times lower than that of Nafion^® 117 under the same measurement conditions. A maximum proton permselectivity of 96 × 10³ S cm⁻³ s, which is defined as the ratio of the proton conductivity to the permeability of methanol, was obtained for this PEM. The permselectivity value is about three times higher than that of Nafion^® 117. A passive air-breathing-type DMFC test cell constructed using the PEM delivered 2.4 mW cm⁻² of maximum power density, P_max, at 2 M methanol concentration, which is smaller than the value obtained with Nafion^® 117. However, at high methanol concentrations (>10 M), the P_max of the PEM decreases slightly to 1.6 mW cm⁻² (at a methanol concentration of 20 M), whereas the P_max of Nafion^® 117 falls to almost zero.     

Novel high-performance nanocomposite proton exchange membranes based on poly (ether sulfone)

In the present research, proton exchange membranes based on partially sulfonated poly (ether sulfone) (S-PES) with various degrees of sulfonation were synthesized. It was found that the increasing of sulfonation degree up to 40% results in the enhancement of water uptake, ion exchange capacity and proton conductivity properties of the prepared membranes to 28.1%, 1.59 meq g⁻¹, and 0.145 S cm⁻¹, respectively. Afterwards, nanocomposite membranes based on S-PES (at the predetermined optimum sulfonation degree) containing various loading weights of organically treated montmorillonite (OMMT) were prepared via the solution intercalation technique. X-ray diffraction patterns revealed the exfoliated structure of OMMT in the macromolecular matrices. The S-PES nanocomposite membrane with 3.0 wt% of OMMT content showed the maximum selectivity parameter of about 520,000 S s cm⁻³ which is related to the high conductivity of 0.051 S cm⁻¹ and low methanol permeability of 9.8 × 10⁻⁸ cm² s⁻¹. Furthermore, single cell DMFC fuel cell performance test with 4 molar methanol concentration showed a high power density (131 mW cm⁻²) of the nanocomposite membrane at the optimum composition (40% of sulfonation and 3.0 wt% of OMMT loading) compared to the Nafion^®117 membrane (114 mW cm⁻²). Manufactured nanocomposite membranes thanks to their high selectivity, ease of preparation and low cost could be suggested as the ideal candidate for the direct methanol fuel cell applications.     

Fabrication and properties of poly(vinyl alcohol)-based polymer electrolyte membranes for direct methanol fuel cell applications

A series of poly(vinyl alcohol) (PVA)-based organic–inorganic crosslinked polymer electrolyte membranes with PVA and poly(methacrylic acid-2-acrylamido-2-methyl-1-propanesulfonic acid-vinyltriethoxysilicone) (PMAV) are prepared for direct methanol fuel cell applications. Fourier transform infrared (FTIR) spectroscopy measurements clearly reveal the existence of crosslinking reactions and molecular interactions in PVA–PMAV membranes. The results of TGA show that the PVA–PMAV membranes possess good thermal stability. The uptake behavior, methanol diffusion coefficient, proton conductivity and selectivity of membranes also are investigated as function of PMAV content. The results indicate that the PVA-based organic–inorganic crosslinked membranes are particularly promising to be used as polymer electrolyte membranes due to their excellent methanol barrier property, suitable proton conductivity and high selectivity.