Pure Nafion Membrane Research Articles

Synthesis and Characterization of Nafion-SiO2 Composite Membranes as an Electrolyte for Medium Temperature and Low Relative Humidity

The weakness of the Nafion membrane as electrolyte of PEMFC associated with physical properties that is easy to shrink at temperatures above 80°C due to dehydration. Shrinkage will decrease the conductivity and membrane damage. Nafion-SiO 2 composite membranes can improve membrane stability. The role of SiO 2 in the Nafion clusters is as water absorbent cause the membrane remains wet at high temperatures and low humidity and conductivity remains high. The results showed the content of 2.8 wt% of SiO 2 in the Nafion membrane, the conductivity of composite membrane is higher than the pure Nafion membrane that are 0.127 S cm -1 in dry conditions and 0.778 S cm -1 in wet conditions at room temperature. Compared with the pure Nafion membrane conductivity are 0.0661 S cm -1 and 0.448 S cm -1 respectively in dry and wet conditions.

Crystallinity Enhancement of Nafion Electrolyte Membranes Assisted by a Molecular Gelator

Nanocrystallites, acting as physical cross-links in Nafion membranes, play a crucial role in building blocks for improving mechanical durability and stopping fuel crossover. However, Nafion membranes suffer from low crystallinity due to the irregular pendent side chains, which hinder self-aggregation of the poly(tetrafluoroethylene) (PTFE) backbones. For the first time, a molecular gelator was introduced in the membrane casting process to enhance the rate of self-assembly of PTFE backbones so as to increase the membrane's crystallinity as well as proton conductivity without sacrificing the purity of Nafion. The molecular gelator used was 3,4-dimethylbenzaldehyde (DMBA). Addition of 0.5 wt % DMBA led to a 42% increase in crystallinity, a 32% increase in yield strength, a 22% increase in tensile modulus and an 18% increase in proton conductivity at 60 °C and 90% relative humidity. Additionally, the membrane electrode assembly (MEA) prepared from the membranes cast from the solution containing 0.5 wt % DMBA also showed an increase of 17% in maximum power density in comparison to the MEA prepared from pure Nafion membrane in a single cell polarization test without any external humidification. Transmission electron microscopy (TEM) and molecular dynamics simulation were used to elucidate the structural changes in Nafion membrane due to the introduction of DMBA. It was observed that the presence of DMBA gives wider crystalline regions under TEM. The molecular dynamics simulation at 500 K shows that the PTFE backbones become elongated in the presence of DMBA due to the enhanced mobility. This is consistent with the observed increase in crystallinity in the membrane as it means reduced entropic change upon crystallization.

Mineral nanofibre reinforced composite polymer electrolyte membranes with enhanced water retention capability in PEM fuel cells

Palygorskite as a type of natural mineral fiber with nano-size channel structure has been introduced into Nafion matrix to enhance both water retention capability and mechanical properties of the Nafion membrane. This composite membrane would increase water uptake by 10% more than pure Nafion membrane at 373 K and be much more stable in dimensional change. Characterized by thermal mechanical analysis (TMA), its mechanical properties were improved by 25% comparing with the pristine Nafion membrane. We also found that the palygorskite in Nafion matrix enhanced the proton conductivity of composite membrane by 75% more than pristine Nafion membrane at 0% RH. Therefore, this work provides a facile approach to improve performance of Nafion membranes by introducing one-dimensional hydrophilic mineral nanofibre into Nafion matrix.

Neodymium triflate modified nafion composite membrane for reduced alcohol permeability in direct alcohol fuel cell

This paper reports an experimental study on the modification of nafion membrane with neodymium triflate, Nd(SO3CF3)3, a rare earth triflate. The triflate ion resembles nafion in structure and has high lewis acidity, high coordination number, hygroscopic nature and thermal stability. These properties make the neodymium triflate (NdTfO) suitable to improve the performance of NdTfO/nafion membranes in direct alcohol fuel cell by reducing fuel permeability without compromising other properties. The NdTfO/nafion membranes reduced alcohol permeability by nearly 48%. The proton conductivity of 1% NdTfO/nafion was increased by at least 24% as compared to pure cast nafion membrane. The mechanical strength of 1% NdTfO/nafion was higher than that of pure cast nafion. The composite membrane was thermally and chemically stable and has potential for use in direct alcohol fuel cells. A DMFC was developed and its performance was evaluated using the composite membrane, which showed encouraging results.

Correlation of structural differences between Nafion/polyaniline and Nafion/polypyrrole composite membranes and observed transport properties

Polyaniline/Nafion and polypyrrole/Nafion composite membranes, prepared by chemical polymerization, are studied by scanning electron microscopy, infrared and nuclear magnetic resonance spectroscopy. Differences in vanadium ion diffusion through the membranes and in the membranes’ area specific resistance are linked to analytical observations that polyaniline and polypyrrole interact differently with Nafion. Polypyrrole, a weakly basic polymer, binds less strongly to the sulfonic acid groups of the Nafion membrane. Infrared spectroscopy results suggest that the hydrophobic polymer aggregates in the center of the Nafion channel rather than attaching to the hydrophilic walls containing sulfonic acid groups. This results in a drastically elevated membrane resistance and only slightly decreased vanadium ion diffusion compared to a Nafion membrane. Polyaniline, on the other hand, polymerizes along the sides of the Nafion pores and on the membrane surface, binding tightly to the sulfonic acid groups of Nafion, polyaniline's greater basicity possibly causing the difference in polymerization behavior. This leads to a more effective reduction in vanadium ion transport across the polyaniline/Nafion membranes and the increase in membrane resistance is less severe. The performance of selected polypyrrole/Nafion composite membranes is tested in a static vanadium redox cell. Increased coulombic efficiency, compared to a cell employing a pure Nafion membrane, further confirms the reduced vanadium ion transport through the composite membranes.

Self-assembly of durable Nafion/TiO 2 nanowire electrolyte membranes for elevated-temperature PEM fuel cells

TiO 2 nanowire-reinforced Nafion composite membranes for elevated temperature fuel cells are developed by self-assembly of positively charged TiO 2 nanowires and negatively charged Nafion molecules at low pH value condition. The TiO 2 nanowires are synthesized using a hydrothermal process. The Nafion-TiO 2 nanowire composite membrane, in which TiO 2 nanowires were dispersed uniformly, is prepared by solution-casting assisted with self-assembly. At 50 RH% and 90 °C, the cell assembled with Nafion/TiO 2 nanowires composite membranes (5 wt% TiO 2) has a relatively stable performance, and achieves a voltage of 0.59 V at a current density of 600 mA cm −2, about 93% of that at 100 RH%. Self-assembly of the TiO 2 nanowire also improves the mechanical properties of the composite membrane both at different temperatures and humidity conditions. At the temperature close to the glass transition temperature, the TiO 2 nanowires remarkably reinforce the physical dimension of the membrane when the Nafion polymer structure is destroyed. In an in situ RH-cyclic accelerating experiment, the degradation of the open circuit voltage of the fuel cell assembled with Nafion-TiO 2 nanowire composite membrane (5 wt%) reaches 6.1 mV/h, compared to 16.3 mV/h for a fuel cell assembled with a recasting of pure Nafion membrane.

Nafion®—titania nanocomposite proton exchange membranes

AbstractProton exchange membranes consisting of Nafion® and crystallized titania nanoparticles have been developed to improve water‐retention and proton conductivity at elevated temperature and low relative humidity. The anatase‐type titania nanoparticles were synthesized in situ in Nafion solution through sol–gel process and the size of the formed titiania nanoparticles is in the range of 3–6 nm. The formed nanoparticles are well‐dispersed in Nafion solution at the titania concentration of 5 wt %. The glass transition temperature of the formed Nafion‐titania composite membrane is about 20oC higher than that of plain Nafion membrane. At elevated temperature (above 100°C), the Nafion‐titania nanocomposite membrane shows higher water uptake ability and improved proton conductivity compared to pure Nafion membrane. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Synthesis and characterization of neodymium oxide modified nafion membrane for direct alcohol fuel cells

Nafion composite membranes were prepared by incorporating neodymium oxide (Nd 2O 3), a hygroscopic rare earth oxide and a dopant for H + ion conduction, into the nafion structure. Five different loadings of Nd 2O 3 were used to fabricate Nd 2O 3/nafion composite membranes and characterized extensively for possible use in direct alcohol fuel cells. The proton conductivity, ion exchange capacity, water uptake, tensile strength, and oxidation stability of the composite membrane were higher than pure cast nafion membrane. Nd 2O 3/nafion composite membrane exhibited reduced methanol and ethanol crossover as compared to pure cast nafion membrane and thus has potential to use in direct alcohol fuel cells.

Investigation of physical properties and cell performance of Nafion/TiO 2 nanocomposite membranes for high temperature PEM fuel cells

Synthesis and characterization of Nafion/TiO 2 membranes for proton exchange membrane fuel cell (PEMFC) operating at high temperatures were investigated in this study. Nafion/TiO 2 nanocomposite membranes have been prepared by in-situ sol–gel and casting methods. In the sol–gel method, preformed Nafion membranes were soaked in tetrabutylortotitanate (TBT) and methanol solution. In order to compare synthesis methods, a Nafion/TiO 2 composite membrane was fabricated with 3 wt.% of TiO 2 particles by the solution casting method. The structures of membranes were investigated by Differential Scanning Calorimetry (DSC), Scanning Electron Microscopy (SEM), and Energy Dispersive X-Ray Analysis (EDXA). Also, water uptake and proton conductivity of modified membranes were measured. Furthermore, the membranes were tested in a real PEMFC. X-Ray spectra of the composite membranes indicate the presence of TiO 2 in the modified membranes. In case of the same doping level, sol–gel method produces more uniform distribution of Ti particles in Nafion/TiO 2 composite membrane than the ones produced by casting method. Water uptake of Nafion/TiO 2 membrane with 3 wt.% of doping level was found to be 51% higher than that of the pure Nafion membrane. EIS measurements showed that the conductivity of modified membranes decreases with increasing the amount of doped TiO 2. Finally, the membrane electrode assembly (MEA) prepared from Nafion/Titania nanocomposite membrane shows the highest PEMFC performance in terms of voltage vs. current density (V–I) at high temperature (110 °C) which is the main goal of this study.

Nafion−Montmorillonite Nanocomposite Membrane for the Effective Reduction of Fuel Crossover

The effect of Nafion−clay nanocomposite membranes on hydrogen and methanol crossover in a proton exchange membrane (PEM) fuel cell was studied. Several analytical methods were used to determine the fuel crossover rate and the ionic conductivity of the membranes. It is the first time a Nafion−clay nanocomposite was investigated to reduce the hydrogen migration rate across the PEM membrane. The Nafion−clay nanocomposites demonstrated significantly reduced permeability to both methanol and hydrogen. The reduction of hydrogen and methanol crossover was compared, and the possible mechanistic difference was discussed. The ionic conductivities for both in-plane and through-plane were measured using alternating current impedance techniques. The ionic conductivities of the Nafion−clay nanocomposites were lower than a pure Nafion membrane of the same thickness.

Acid-Functionalized Polysilsesquioxane−Nafion Composite Membranes with High Proton Conductivity and Enhanced Selectivity

A series of new Nafion-based composite membranes have been prepared via an in situ sol-gel reaction of 3-(trihydroxylsilyl)propane-1-sulfonic acid and solution casting method. The morphological structure, ion-exchange capacity, water uptake, proton conductivity, and methanol permeability of the resulting composite membranes have been extensively investigated as functions of the content of sulfopropylated polysilsesquioxane filler, temperature, and relative humidity. Unlike the conventional Nafion/silica composites, the prepared membranes exhibit an increased water uptake and associated enhancement in proton conductivity compared to unmodified Nafion. In particular, considerably high proton conductivities at 80 and 120 degrees C under 30% relative humidity have been demonstrated in the composite membranes, which are over 2 times greater than that of Nafion. In addition to a remarkable improvement in proton conductivity, the composite membranes display lower methanol permeability and superior electrochemical selectivities in comparison to the pure Nafion membrane. These unique properties could be exclusively credited to the presence of pendant sulfonic acid groups in the filler, which provides fairly continuous proton-conducting pathways between filler and matrix in the composite membranes and thus facilitates the proton transport without the anticipated trade-off between conductivity and selectivity. This work opens new opportunities of tailoring the properties of Nafion-the benchmark fuel cell membrane-to obviate its limitations and enhance the conductive properties at high temperature/low humidity and in direct methanol fuel cells.

Nafion/Analcime and Nafion/Faujasite composite membranes for polymer electrolyte membrane fuel cells

The Nafion/zeolite composite membranes were synthesized for polymer electrolyte fuel cells (PEMFCs) by adding zeolite in the matrix of Nafion polymer. Two kinds of zeolites, Analcime and Faujasite, having different Si/Al ratio were used. The physico-chemical properties of the composite membranes such as water uptake, ion-exchange capacity, hydrogen permeability, and proton conductivity were determined. The fabricated composite membranes showed the significant improvement of all tested properties compared to that of pure Nafion membrane. The maximum proton conductivity of 0.4373 S cm −1 was obtained from Nafion/Analcime (15%) at 80 °C which was 6.8 times of pure Nafion (0.0642 S cm −1 at 80 °C). Conclusively, Analcime exhibited higher improvement than Faujasite.

Nafion–zirconia nanocomposite membranes formed via in situ sol–gel process

Crystallized zirconia nanoparticles with diameters of 6.3 ± 0.5 nm were in situ formed in Nafion solution through sol–gel process. Nafion molecules were self-assembled onto zirconia nanoparticles through electrostatic interactions and prevent the further growth of initial formed particles. The Nafion–zirconia nanocomposite membranes were formed using a recasting process. It was found that the addition of zirconia nanoparticles did not affect the crystallinity and structure of Nafion in the membrane significantly. The formed Nafion–zirconia nanocomposite membrane shows enhanced water retention ability at 100 °C compared to recast pure Nafion membrane, especially at medium and high relative humidity. This work demonstrates the potential of Nafion–zirconia nanocomposite membranes for PEMFC applications.

A novel composite Nafion membrane for direct alcohol fuel cells

Trifluoromethanesulfonic acid or triflate acid, chemical formula CF 3SO 3H, is regarded as one of the strongest acids and resembles Nafion ® in structure. Erbium triflate, a lanthanum salt of triflate, is thermally stable. This paper reports data on the formation of membranes by the fixation of erbium triflate salts (ErTfO) into the Nafion structure. Five different loadings of ErTfO were used to fabricate ErTfO/Nafion composite membranes and these were characterized, extensively for possible use in direct alcohol fuel cells. The membranes were characterized using XRD, TGA, FTIR, and for mechanical strength, water uptake, ion exchange capacity, alcohol uptake, swelling, proton conductivity, alcohol permeability and oxygen stability. The ErTfO/Nafion composite membranes reduced alcohol permeability by 77–80%. The proton conductivity of 3% ErTfO/Nafion composite membranes was 38% higher than that of a pure cast Nafion membrane. The oxygen stability of the ErTfO/Nafion composite membranes was higher than pure cast Nafion. However, the mechanical strength of 7% and 9% ErTfO/Nafion was lower than that of pure cast Nafion. The composite membrane was chemically stable and has potential for use in direct alcohol fuel cells.

Methanol permeability and proton conductivity of Nafion membranes modified electrochemically with polyaniline

Nafion membrane was modified with polyaniline by electrochemical methods, including constant current, constant potential and potential cycling. The methanol permeability and the proton conductivity of the Nafion membranes with and without modification were determined by the electrochemical oxidation of the permeated methanol and electrochemical impedance spectroscopy, respectively. It is found from FTIR results that the polyaniline formed by electrochemical method is in emeraldine state. With the modification of polyaniline, the methanol permeability of the Nafion membrane is reduced by one decade but there is only a slight decrease in proton conductivity. The power density output of direct methanol fuel cell using polyaniline-modified Nafion membrane is 40% larger than that using pure Nafion membrane. The modification with polyaniline is better than that with polypyrrole. The methanol permeability of the polyaniline-modified Nafion is about half of that of the polypyrrole-modified Nafion but the proton conductivity of the former is higher than the later.

A mechanical durability comparison of various perfluocarbon proton exchange membranes

AbstractMechanical endurance and degradation mechanism of Nafion211 proton exchange membrane and ePTFE/PFSA composite PEMs were investigated in this article. It was found that the shrinkage stress caused by the water‐uptake is the primary source to induce the mechanical decay. The Nafion 211 is more stable when cycle‐stress is lower than 1.5 MPa, while the water‐uptake generating stress can reach to 2.23 MPa soaked in surroundings with condition of 25% RH and temperature at 25°C. The study also found that the ePTFE/PFSA composite PEMs are more durable than the Nafion membrane mostly due to the lower water‐uptake generating shrinkage stress of 0.34–0.4 MPa (25% RH@ 25°C) but not the high yield strength or breaking strength. The PFSA/ePTFE composite membranes can keep stable for more than 5000 cycles, which is about 40% higher than that of the pure Nafion membrane (about 3500 cycles.). For preparing durable proton exchange membrane, it is necessary to improve the proton exchange resin impregnation in the ePTFE matrix. Chemical bonding of the PTFE and the PSFI by modification of the PTFE matrix is also very effective to enhance the mechanical durability of the composite PEMs. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

A Nafion-based self-humidifying membrane with ordered dispersed Pt layer

A double-layer Nafion-based membrane consisting of a pure Nafion layer and an ordered dispersed Pt particles layer was investigated. The Pt particles were dispersed under the anode graphite ribs, which provide the sites for the recombination of the permeating H 2 and O 2 into water. The electrochemical performances of the ordered Pt particles dispersed membrane in proton exchange membrane fuel cell (PEMFC) were studied and compared with those of the common Pt particles dispersed membrane and the pure Nafion membrane. The results indicate that the ordered Pt dispersed membrane reduces the amount of Pt dosage than the common Pt dispersed membrane and improves the performance of PEMFC operated under dry conditions than the pure Nafion membrane as well.

Composite Membrane Containing a Proton Conductive Oxide for Direct Methanol Fuel Cell

The composite membrane for direct methanol fuel cell (DMFC) was developed using powder and perfluorosulfonylfluroride copolymer (Nafion) resin. The perfluorosulfonylfluroride copolymer (Nafion) resin was mixed with powder and it was made to sheet form by hot pressing. The electrodes were prepared with 60 wt% PtRu/C and 60wt% Pt/C catalysts for anode and cathode, respectively. The morphology and the chemical composition of the composite membrane have been investigated by using SEM and EDXA, respectively. The composite membrane and were analyzed by using FT-IR and XRD. The methanol permeability of the composite membranes was also measured by gas chromatography (GC). The performance of the MEA containing the composite membrane (2wt% ) was higher than that of normal pure Nafion membrane at high operating temperature (e.g. ), due to the homogenous distribution of , which decreased the methanol permeability through the membrane and enhanced the water contents in the composite membrane.

Synthesis and performance of water‐retention PEMs with nafion‐intercalating‐montmorillonite hybrid

AbstractA proton exchange membrane modified with montmorillonite (MMT) was prepared by introducing perfluorosulfonylfluroride resin into the interlayer of MMT at high temperature and high pressure. The intercalating structure was analyzed by wide‐angle X‐ray diffraction (XRD), and the results showed that the polymer was indeed intercalated into the interlayer of the modified montmorillonite (m‐MMT) matrix without destroying the microstructure of the matrix by largely increasing the d‐spacings of m‐MMT. SEM analysis on the surface and cross‐section of these composite membranes shows that the MMT nanoparticles are dispersed in the membrane uniformly. This composite membrane reveals excellent water retention and conductance at high temperature. The composite membrane was evaluated in a single cell, and the results show that the performance of composite membrane is higher than that of pure Nafion membrane at hightemperature especially without external‐humidification. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Design of a low power optical limiter based on a new nanocomposite material incorporating silica-encapsulated phthalocyanine in Nafion

We report on the design of a stable optical limiter in the low laser power regime based on the thermal variation of refractive index in a novel nanocomposite material. The optical material, chloroaluminium-phthalocyanine (ClAlPc), is embedded in SiO2-Nafion nanocomposite membrane (ClSNf) and its thermally induced nonlinear refractive index is characterized by the Z-scan technique with a low power cw He–Ne laser as the source. The value of nonlinear refractive index coefficient, n2, is found to be about 1.11 × 10−11 m2 W−1. The experiment is repeated with the dye doped in pure Nafion membrane (ClNf) and the results are compared with those of ClAlPc doped SiO2–Nafion nanocomposite membrane. The value of n2 is found to be 1.36 × 10−11 m2 W−1 and is larger than that of the ClAlPc embedded SiO2–Nafion nanocomposite membrane. The photostability of the dye-embedded membrane is studied by exposing the sample to cw He–Ne laser and monitoring its fluorescence emission intensity continuously. The samples are found to show large thermal lens effect and demonstrated to be good optical limiters in the low power regime. Whereas the optical properties of dye-doped Nafion appear to be slightly better than those of the dye embedded in silica and incorporated in Nafion, the latter is found to offer excellent photostability.