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A direct methanol fuel cell (DMFC) is an excellent energy device in which direct conversion of methanol to energy occurs, resulting in a high energy conversion rate. For DMFCs, fluoropolymer copolymers are considered excellent proton-exchange membranes (PEMs). However, the high cost and high methanol permeability of commercial membranes are major obstacles to overcome in achieving higher performance in DMFCs. Novel developments have focused on various reliable materials to decrease costs and enhance DMFC performance. From this perspective, cellulose-based materials have been effectively considered as polymers and additives with multiple concepts to develop PEMs for DMFCs. In this review, we have extensively discussed the advances and utilization of cost-effective cellulose materials (microcrystalline cellulose, nanocrystalline cellulose, cellulose whiskers, cellulose nanofibers, and cellulose acetate) as PEMs for DMFCs. By adding cellulose or cellulose derivatives alone or into the PEM matrix, the performance of DMFCs is attained progressively. To understand the impact of different structures and compositions of cellulose-containing PEMs, they have been classified as functionalized cellulose, grafted cellulose, acid-doped cellulose, cellulose blended with different polymers, and composites with inorganic additives. [ABSTRACT FROM AUTHOR]

Perfluorosulfonic acid Nafion membranes are widely used as an electrolyte in electrolysis processes and in fuel cells. Changing the preparation and pretreatment conditions of Nafion membranes allows for the optimization of their properties. In this work, a Nafion-NMP membrane with a higher conductivity than the commercial Nafion® 212 membrane (11.5 and 8.7 mS∙cm−1 in contact with water at t = 30 °C) and a comparable hydrogen permeability was obtained by casting from a Nafion dispersion in N-methyl-2-pyrrolidone. Since the ion-exchange capacity and the water uptake of these membranes are similar, it can be assumed that the increase in conductivity is the result of optimizing the Nafion-NMP microstructure by improving the connectivity of the pores and channels system. This leads to a 27% increase in the capacity of the membrane electrode assembly with the Nafion-NMP membrane compared to the Nafion® 212 membrane. Thus, the method of obtaining a Nafion membrane has a great influence on its properties and performance of fuel cells based on them. [ABSTRACT FROM AUTHOR]

In this study, we performed small-angle X-ray scattering (SAXS) to investigate the structure of Nafion® membranes. The effect of freeze/thaw (F/T) cycles (from ambient temperature down to −40 °C) on the membrane nanostructure was considered for the first time. The SAXS measurements were taken for different samples: a commercial Nafion® 212 membrane swollen in water and methanol solution, and a water-swollen silica-modified membrane. The membrane structure parameters were obtained from the measured SAXS profiles using a model-dependent approach. It is shown that the average radius of water channels (Rwc) decreases during F/T cycles due to changes in the membrane structure as a result of ice formation in the pore volume after freezing. The use of water-methanol solution (methanol content of 20 vol.%) for the membrane soaking prevents changes in the membrane structure during F/T cycles compared to the water-swollen membrane. Modification of the membrane surface with silica (SiO2 content of 20 wt.%) led to a redistribution of water in the membrane volume and resulted in a decrease in Rwc. However, Rwc for the modified membrane did not decrease with the increasing number of F/T cycles due to the involvement of SiO2 in the sorption of membrane water and, therefore, the prevention of ice formation. [ABSTRACT FROM AUTHOR]

In this work, the effect on the physico-chemical properties of Nafion 117 membrane due to the treatment with HCl, H 2 SO 4 and HNO 3 was studied. Water uptake, crystallinity, proton conductivity and water dynamics were evaluated on treated and non-treated membranes. An increase in the water uptake and conductivity and a decrease in the crystallinity were observed in treated membranes in comparison with the untreated one. The water dynamics, studied by spin-spin NMR relaxometry, suggests that treated membranes have a more uniform channel size distribution. The treatment with HCl and HNO 3 showed higher conductivity and water uptake than H 2 SO 4. [Display omitted] • Modifications in the polymeric channel structure produced by acid treatment. • Changes in the water uptake, crystallinity and proton conductivity due to the acid treatment. • Dynamics of water molecules studied by NMR. [ABSTRACT FROM AUTHOR]

[Display omitted] The local mobility and diffusion of Li+, Na+, and Cs+ cations in Nafion 117 membrane were explored by 7Li, 23Na, and 133Cs spin relaxation and pulsed field gradient NMR techniques. It was shown that the macroscopic mass transfer of cations is controlled by ion motion near sulfonate groups. Lithium and sodium cations, whose hydrated energy is higher than the water hydrogen bond energy, are moving together with water molecules, but cesium cations possessing a low hydrated energy are jumping directly between the neighboring sulfonate groups. [ABSTRACT FROM AUTHOR]

Nafion is one of the polymer materials used as polymer electrode membrane (PEM) for fuel cells. However, the electrochemical reaction and water management processes that occur at the catalyst layer affect the performance and degradation of the membrane in the fuel cell resulting in various degradation mechanisms. Understanding the degradation mechanisms of the Nafion membrane in operation, the anhydrous and electrochemical conditions in the fuel cell is highly a necessity as outlined in this review. This review further recommends that further improvement in the Nafion membrane can be made by fabrication and coating the Nafion membrane with materials that can withstand the electrochemical environment in the fuel cell. • Nafion ionion provides a substantial integral part of the PEMFC performance. • Fuel cell environment affects performance and degradation of Nafion. • Degradation mechanisms in Nafion can be identified through electrochemical tests. • The use of Nano-composite materials enhances the durability of Nafion ionion. [ABSTRACT FROM AUTHOR]

The influence of optimum UV ray exposure of pristine Nafion polymer membranes on the improvement of proton conductivity and hydrogen fuel cell performance has been examined. Nafion membranes with thickness 183 μm (117), 90 μm (1035), 50 μm (212) and 25 μm (211) were irradiated with ultraviolet rays with doses in the range 0–250 mJ cm−2 and their proton conductivities have been measured with standard method. The Nafion membranes have also been studied by measuring their water uptake, swelling-ratios and porosity using standard procedures. Hydrogen fuel cells with dual serpentine microchannels with active area 1.9 x 1.6 cm-2 were assembled with anode gas diffusion layer, Nafion membrane, cathode gas diffusion layer and other components. An external humidifier was used to humidify hydrogen for the fuel cell. The experimental Results have shown an increase in the value of Nafion proton conductivity with an optimum UV irradiation which depends on the thickness of Nafion membrane: the optimum doses for peak proton conductivity were 196mJ/cm−2 for Nafion 117, 190mJ/cm−2for Nafion 1035, 180mJ/cm−2 for Nafion 212 and 160mJ/cm−2 for Nafion 211. This enhancement of proton conductivity is because of the optimal photo-crosslinking of –SO 3 H groups in Nafion. This causes optimum pore-size in Nafion thereby facilitating increased proton-hopping between –SO 3 H sites in Nafion. Hydrogen fuel cells were developed with pristine as well as with optimal UV irradiated Nafion with thicknesses of 90 and 50 μm. The polarization plots obtained for these devices showed an increase in power densities approximately by a factor of 1.8–2.0 for devices with optimally UV irradiated Nafion. These results indicate that optimal UV irradiation of Nafion is an excellent technique for enhancing power output of hydrogen fuel cells. [Display omitted] • The optimum dose of UV rays on Nafion enhances proton conductivity. • Tuning of pores in Nafion membranes by UV ray irradiation. • Optimization of hydrogen humidification for better power output. • Optimum UV irradiation dose depends on the membrane thickness. [ABSTRACT FROM AUTHOR]

In this work, we printed a Nafion precursor membrane by fused deposition modeling (FDM) rapid prototyping technology and further fabricated IPMCs by electroless plating. The ion-exchange capacity of the Nafion membrane was tested, and the morphology of IPMCs was observed. The electro-mechanical properties of IPMCs under AC voltage inputs were studied, and grasping experiments were performed. The results show that the Nafion membrane after hydrolysis has a good ion-exchange ability and water-holding capacity. SEM observed that the thickness of the IPMC's electrode layer was about 400 nm, and the platinum layer was tightly combined with the substrate membrane. When using a square wave input of 3.5 V and 0.1 Hz, the maximum current of IPMCs reached 0.30 A, and the displacement and blocking force were 7.57 mm and 10.5 mN, respectively. The new fabrication process ensures the good driving performance of the printed IPMC. And two pieces of IPMCs can capture the irregular objects successfully, indicating the feasibility of printing IPMCs by FDM technology. This paper provides a new and simple method for the fabrication of three-dimensional IPMCs, which can be further applied in flexible grippers and soft robotics. [ABSTRACT FROM AUTHOR]

Removing iron, aluminum, and magnesium ions from the primary wet-process phosphoric acid solution (WPA) is a promising strategy for mitigating scaling in downstream processing. Here, Donnan dialysis using Nafion membranes, with HNO 3 as the stripping solution, was proposed and evaluated. The species in WPA as a function of temperature were modeled. The influence of HNO 3 molarity (1–5 M), temperature (25–65 °C), and Nafion membrane type on the metal ion mass transport was systematically studied. The effect of H 3 PO 4 molarity on the metal ion mass transport was analyzed with synthetic WPA solutions, considering the form (free cation or complexed with anions) in which these metal ions transport through the membrane by analyzing the ionic composition of membranes in equilibrium with WPA. The coupled cation diffusion coefficients in membranes are modeled via the Nernst - Planck flux equation. It is found that the cation flux always follows this order: J Mg > J Al > J Fe for WPA. These factors can be attributed to: 1) in WPA Mg appears mostly as Mg2+, while almost all Fe ions and around half the Al ions are in a paired state, giving the bulky Fe(H 2 PO 4)2+, Al(SO 4)+ and Al(SO 4) 2 -, respectively; 2) only solution viscosity influences the Mg2+ transport, while both the solution viscosity and the complexation with anions influence Fe and Al transport; 3) Mg2+ ions have the largest diffusion coefficient in the membrane phase. These metal ions transport in the form of free cations through the membranes. It is concluded that Donnan dialysis is suitable for removing the fast-diffusing Mg2+ ions from diluted WPA, and increasing the solution temperature could enhance the Mg2+ transport rate. [Display omitted] • Removing metal ions from wet-process phosphoric acid (WPA) solution. • Species of Fe, Al and Mg in WPA solution were modeled. • Ionic fluxes through membranes follow the order: Mg2+>Al3+>Fe3+. • Ion pairing and solution viscosity influence Fe, Al transport. • Donnan dialysis was effective for removing Mg2+ from WPA solution. [ABSTRACT FROM AUTHOR]

[Display omitted] Correlation times and diffusion coefficients of water molecules were measured for the first time by 1H spin relaxation and pulsed field gradient NMR in Li+, Na+ and Cs+ ionic forms of Nafion 117 membrane. Hydration numbers of Li+, Na+ and Cs+ cations were calculated. It was shown that at high humidity macroscopic transfer is controlled by the local translational motion of water molecules. [ABSTRACT FROM AUTHOR]

Summary: A double chamber microbial fuel cell (MFC) reactor with anode and cathode chamber separated by a Nafion proton exchange membrane was developed and performance was evaluated for treatment of electro Fenton pretreated latex processing and production wastewater containing chemical oxygen demand of 2660 and 780 mg L−1, respectively. After 12 days, MFC treatment, the COD reduced to 133 mg/L (96%) and 86 mg/L (88.5%) for latex processing and production wastewater respectively. The MFC treatment system generated electrical energy of 1.57 and 1.04 Wh L−1 for latex processing and production wastewaters respectively that was utilized to drive the electro‐Fenton reactor. These results indicated that effective wastewater treatment, energy production, and discharge standards could be obtained in the system. [ABSTRACT FROM AUTHOR]

[Display omitted] The modification of Nafion® membranes with poly(diallyldimethylammonium chloride) (PDDA) in aqueous solutions of isopropanol has been investigated. A remarkable decrease in vanadyl ion permeability (by 3.5 orders of magnitude), accompanied by a decrease in proton conductivity sixfold at most, was found for Nafion membranes modified in 30–35 wt% isopropanol solutions providing a high swelling of the membranes. The Bradford reagent has been used for the detection of PDDA on the membrane surface. [ABSTRACT FROM AUTHOR]

Microbial fuel cells (MFCs) are the most useful technologies for energy production and wastewater treatment due to their low cost and support of the environment. In this study, the membrane fouling and their effects on power generation were investigated using scanning electron microscope (SEM). Results demonstrate that proton exchange membrane (PEM) was affected by biofouling in a two-chamber H-type MFC, which would significantly affect coulombic efficiencies (CEs), and maximum power densities leading to reduced power generation. The power densities of both rice straw and potato peels were 119.35 mW/m2 and 152.55 mW/m2, respectively. Scanning Electron Microscope (SEM) showed substantial accumulation of bacteria and their end-products forming a thick biofilm on the surface of PEM leading to a decrease, if not, preventing the passage of protons from the anode side toward the cathode side. The decline in power generation may result mainly from the biofouling, not of electrodes but, of PEM membrane from both sides (Anode and Cathode) because of improper regular PEM cleaning. • Electricity generation from rice straw using microbial fuel cell technologies. • Characterization of membrane biofouling by SEM and other parameters. • Effect of biofouling on performance of long-term operation of MFC. • The biofouled membrane could be used after cleaning. [ABSTRACT FROM AUTHOR]

Zn2+, Cu2+, and Ni2+ ionic permeabilities through a Nafion 115 membrane, containing sulfonate functional groups capable of cation exchange with metal ions, were measured in this work. Single and binary salt mixtures were prepared at 10, 100, and 1000 ppm concentrations, and the ionic permeabilities and selectivities (α) were measured. The ionic permeabilities were in the 10−6–10−5 cm2/s range, and the order of ion permeability depends on the ionic concentration. At low (10 ppm) concentration, the smaller Ni2+ transported faster than the other two ions and the permeability was dominated by the ionic diffusivity. As the concentration was increased to 100 and 1000 ppm, the ion permeability was increased because more ions were exchanged onto the sulfonate groups. Moreover, Zn2+ became the fastest ion among the three as the ion transport became solubility-controlled at the medium and high concentrations. In spite of the ion permeability order being dependent upon the feed concentration, the separation selectivity was not affected by the presence of co-ions in the tested conditions. The separation selectivity from a binary mixture could be estimated from the permeability ratio obtained from single solutions. [ABSTRACT FROM AUTHOR]

[Display omitted] • Nafion doped polyaniline/graphene oxide composites are synthesized for the first time and used as the electrode materials of supercapacitors. • Polyaniline utilization rate and electrochemical surface area are improved by Nafion doping in the Nafion membrane-based supercapacitors. • Graphene oxide can enhance the electrochemical stability of polyaniline in the Nafion doped polyaniline/graphene oxide composites. • Flexible supercapacitor shows 300F g−1 at bent condition, which is the maximum value among reported Nafion membrane-based supercapacitors. • After 1000 cycles, the capacitance retention rate of the composites is 83.0%, which is higher than that of Nafion doped polyaniline (72.1%). Nafion membrane possesses good ionic conductivity and excellent mechanical stability, which can be used as electrolyte and separator of flexible supercapacitor. However, due to its solid-state structure, it is difficult for the Nafion membrane to permeate in solid-state electrode, which reduces electrochemical surface area, and increases interface resistance. The electrode materials need to be carefully designed to solve the above issues. In this study, Nafion doped polyaniline/graphene oxide composites were designed and synthesized as electrode materials to fabricate flexible supercapacitors based on Nafion membrane. The polyaniline utilization rate and the electrochemical surface area are improved by Nafion doping. In addition, the electrostatic interaction between polyaniline and Nafion can reduce the interface resistance. Graphene oxide can enhance the polyaniline electrochemical stability. The specific capacitances of flexible supercapacitor are 309 and 300F g−1 under flat and bent conditions (at 1 A/g), respectively, which are the maximum values among reported Nafion membrane-based supercapacitors. After 1000 cycles, the capacitance retention rate of supercapacitor with Nafion membrane is 87.2%, which is higher than that with H 2 SO 4 electrolyte (83.0%). Therefore, the Nafion membrane-based flexible supercapacitor has widespread applications in electronic products because of its high performance and good cycling stability. [ABSTRACT FROM AUTHOR]

Here we introduce the new approach to high-efficiency power generation from a salinity difference using conventional nanoporous Nafion membrane. When access areas on each side of nanoporous Nafion membrane are set to be asymmetric, the ratio of ionic current upon a voltage bias of the different polarity also becomes asymmetric, resulting in ionic diode phenomena. When this geometrical ionic diode effect is combined with a salinity gradient, it can help significantly improve the energy conversion efficiency from a salinity difference even under a hyper-saline environment with a large salinity difference, e.g. ∼41% conversion efficiency and ∼120 nW power generation with 1 M KCl and 1000-fold salinity difference, both of which are comparable with the best performances reported in the previous studies. We propose that the decrease in ion concentration polarization at a low salt concentration side is responsible for the enhanced power generation with the membrane having asymmetric access areas. Our approach is simple to implement and can be applicable to any nanoporous membrane to enhance the power generation from a salinity difference. [ABSTRACT FROM AUTHOR]

Sulfonated covalent organic nanosheets (SCONs) with a functional group (−SO 3 H) are effective at reducing ion channels length and facilitating proton diffusion, indicating the potential advantage of SCONs in application for proton exchange membranes (PEMs). In this study, Nafion-SCONs composite membranes were prepared by introducing SCONs into a Nafion membrane. The incorporation of SCONs not only improved proton conductivity, but also suppressed methanol permeability. This was due to the even distribution of ion channels, formed by strong electrostatic interaction between the well dispersed SCONs and Nafion polymer molecules. Notably, Nafion-SCONs-0.6 was the best choice of composite membranes. It exhibited enhanced performance, such as high conductivity and low methanol permeability. The direct methanol fuel cell (DMFC) with Nafion-SCONs-0.6 membrane also showed higher power density (118.2 mW cm−2), which was 44% higher than the cell comprised of Nafion membrane (81.9 mW cm−2) in 2 M methanol at 60 °C. These results enabled us to work on building composite membranes with enhanced properties, made from nanomaterials and polymer molecules. Image 1 • Nanosheets with high proton conductivity were incorporated into Nafion membrane. • Composite membranes showed enhanced proton conductivity and reduced methanol crossover. • Composite membrane showed high power density in fuel cell testing. [ABSTRACT FROM AUTHOR]

Bioelectrochemical systems are devices where organic matter (e.g. wastewater) is oxidized through exoelectrogenic bacteria; this process is a new alternative to energy crisis and to mitigate climate change. If the products of such oxidation are electrons they are called microbial fuel cell (MFC), otherwise if the product is hydrogen these devices are called microbial electrolysis cells (MEC) Mostly, MEC's studies have reported double chamber designs, where the anode and cathode are separated by an ion exchange membrane. Nafion is a proton exchange membrane widely used to study bioelectrochemical devices; however, to our knowledge there are no reports of bipolar membranes (BPM) in these systems. In this study, a double-chambered MEC was constructed to evaluate the performance of the system using Nafion® 117, and FUMASEP® FBM bipolar membrane, separately. Biofilm formation was monitored by cyclic voltammetry and open circuit potential (OCP); maximum power for MFC-Nafion and MFC-BPM were 105.1 and 3.6 mW/m2, respectively. Hydrogen yield and COD removal were significantly different for both MEC systems. Whereas COD removal for MEC-BPM was 44.8%; MEC-Nafion exhibited a COD removal of 87.4%. Solely the latter system produced hydrogen, with a yield of 7.6%. • Wastewater used as substrate with minimum pretreatment and conditioning. • Nafion 117 exhibited a lower internal resistance compared to BPM. • COD removal of the MEC-Nafion system was almost double the MEC-BPM. • Up to 4 mL*L−1*d−1 were solely produced in the MEC-Nafion system. [ABSTRACT FROM AUTHOR]

Nanoheterostructured material composed of sepiolite clay mineral in which is assembled a MgAl layered double hydroxide (LDH) was used in the preparation of Nafion composite electrolyte membranes and their behavior compared to those of membranes filled with the LDH alone. Both, the neat MgAl LDH and the MgAl LDH-sepiolite hybrid materials were obtained via the co-precipitation method. Sepiolite fibers provide a large external surface area for bonding MgAl LDH particles while maintaining high microporosity and water molecules. The nanocomposite membranes were prepared incorporating different amount of LDH or LDH-sepiolite hybrid. Composite membranes present better water retention, good thermal properties and high proton conductivities at high temperatures than the pure Nafion membrane. The proton conductivity at 100 °C and 100% RH reaches a value of 0.13 S/cm for the LDH-sepiolite Nafion membrane whereas is only 0.010 S/cm in the case of the Nafion membrane. Fuel cell tests using Nafion membranes containing LDH or LDH-sepiolite hybrid as composite electrolytes show a good result for the operation of the PEMFC at 80 °C, 100 °C and 110 °C, with a clear favoring effect of the LDH-sepiolite filler for operation at the highest temperatures. • Incorporation of LDH (MgAl) and hybrid MgAl-sepiolite in Nafion membrane. • Improved properties of Nafion membrane; water retention and proton conductivity. • Fuel cells performance of the composite membranes at high temperature. [ABSTRACT FROM AUTHOR]

Abstract The isotopic composition of water (2H/1H and 18O/16O) has been widely used in hydrology, ecology, paleoclimatology and forensic science. However, sampling frequency limits many such studies and there is now a clear need for field-portable mass spectrometer and laser-based spectrometer devices to measure water isotopic composition in-situ and at high temporal resolution. Here we explore the use of Nafion membranes as a potential Membrane Introduction (MI) inlet system for high frequency isotope analysis. As yet, the fractionation behaviour of 2H/1H and 18O/16O isotopic ratios in water transported through Nafion membranes has not been investigated. We quantify this behaviour for water samples with different matrices (organic matter and pollutants) and salinity concentrations across a wide range of isotopic ratios and different membrane thicknesses. Nafion membranes showed no fractionation effects on reported isotope ratios for natural waters. Also no fractionation effects were detected with salinity. Membrane thickness affected slightly the precision and accuracy of the isotopic ratio analysis and our tests showed that thinner Nafion membranes provide better results. However, for samples contaminated with organic matter, the thicker membranes performed better for the 2H/1H isotopic ratio, while for samples contaminated with pollutants, the thicker membranes performed better for the 18O/16O isotopic ratio. Overall, Nafion membranes appear well suited to MI inlet use and our work suggests that the optimal Nafion membrane thickness is 50–150 µm. Highlights • Fractionation of O and H stable isotopes in water through the use of Nafion membranes was examined. • Influence of matrices (organic matter, pollution) on isotopic fractionation was studied. • There was no influence of water salinity on isotopic fractionation. • The use of Nafion membranes as inlet for in-line monitoring of O and H stable isotopes in water is convenient. [ABSTRACT FROM AUTHOR]

Abstract Nafion series cation exchange membranes are extensively investigated and applied in proton exchange membrane fuel cells and flow battery technologies because of their excellent stability and easy availability. However, a deep understanding of their ions transport mechanism and behavior under the alkaline based flow battery media is very limited. Here, the ion transport mechanism through Nafion membrane under alkaline medium is investigated by small-angle X-ray scattering and atomic force microscope techniques. The results indicate that a membrane showed a higher degree of phase separation and larger cluster radius in a NaOH solution than those in a KOH solution, which endows the membrane with a much higher ion conductivity in the NaOH solution. Density functional theory-based simulation also indicates that the adsorption and desorption between the Na+ and the –SO 3 - in Nafion is faster than those of K+. Inspired by these results, an alkaline zinc iron flow battery with a Nafion 212 membrane using NaOH as the supporting electrolyte exhibits a coulombic efficiency of ~ 99% and an energy efficiency of ~ 86% at 80 mA cm−2. This work offers insights into ways to obtain an improved battery performance for the existing as well as the emerging alkaline based flow battery technologies. Graphical abstract fx1 Highlights • Ions transfer behavior and mechanism in Nafion under alkaline media are clarified. • The ions transfer in Nafion is studied via experimental and computational method. • Nafion membrane shows higher ion conductivity in NaOH than those in KOH solution. • A battery using NaOH as supporting electrolyte shows an EE of ~ 86% at 80 mA cm−2. [ABSTRACT FROM AUTHOR]

Abstract The structure of Nafion 117 membranes was studied through SAXS experiments and 2D pattern simulations. Measurements were taken for different moisture conditions by synchrotron radiation, and for different temperatures through X-ray tube irradiation. The experimental profiles were fitted through simulations based on a new structural model including: the amorphous polymer matrix, polymer crystallites, and inverse core-shell type channels conformed by water cylinders and sulfonic chains. The geometrical parameters intervening in the simulation of the SAXS patterns were optimized for each experimental condition. This approach allowed the proper description of the experimental SAXS profiles for the various moisture conditions studied. In addition, a recent lamelar model was also included in the assessments, and the corresponding performances were discussed. Graphical abstract Image 1 Highlights • Nafion 117 membrane structure was studied through SAXS pattern simulations. • Measurements were taken for different moisture conditions and for different temperatures. • A simulation program was developed to produce SAXS profiles for the structure model proposed. • Suitable electron density maps were obtained, based on a core-shell type channel structure. [ABSTRACT FROM AUTHOR]

Due to their preferential cation transport, dense cation exchange membranes like Nafion membranes are unsuitable for Zn/Br redox flow batteries which require bi-ionic transport of Zn 2+ and Br - ions. This work shows that scaling the water cluster size of Nafion membranes by a pre-hydration treatment can achieve not only a high ionic conductivity but also a bi-ionic transport property. Small angle X-Ray scattering, diffusion cell, and electrochemical analysis verify that by increasing the pre-hydration temperature, the water clusters are expanded, resulting in an increase of water uptake, ionic conductivity and the anion transference number. The bi-ionic transport and low area specific resistance induced by the pretreatment enable the successful operation of a Zn/Br redox flow battery with a NRE-212 membrane. Compared with a conventional porous membrane, the properly treated Nafion membrane has an 11.3% higher energy efficiency indicating that the dense structured ion exchange membrane can be used for Zn/Br flow batteries by scaling the water cluster size. [ABSTRACT FROM AUTHOR]

Based on a swelling-filling modification strategy, sheared graphene oxide (SGO) sheets are in -situ inserted into the Nafion membrane and act as bi-functional fillers to simultaneously improve the methanol-permeation resistivity and proton conductivity. Proton/methanol selectivity, as a key descriptor of overall performance of the proton exchange membrane, of the Nafion membrane is therefore 4-fold increased. At the same time, the mechanical, oxidative and thermal stabilities of the Nafion membrane are also improved by the SGO sheets due to the interaction between SGO and Nafion. As a result, the swelling-filling modified SGO -Nafion membrane is therefore considered as a promising electrolyte for direct methanol fuel cell (DMFC) application and the power of the Nafion based DMFC can be improved by ca. 50% during the polarization measurement. [ABSTRACT FROM AUTHOR]

Recently, we have reported a new all tungsto-cobalt heteropoly acid redox flow battery (all H 6 [CoW 12 O 40 ] RFB) with high coulombic efficiency. Because of the relatively large ion size and high negative charge, the tungsto-cobalt heteropoly acid anion is difficult to cross Nafion membrane, which makes it possible to employ thinner Nafion membrane in all H 6 [CoW 12 O 40 ] RFB. In this study, three types of Nafion membranes with different thickness, namely, N212 (50 μm), N211 (25 μm), and N-17 (home-made, 17 μm) are used as polymer electrolyte to investigate its effects on the performance of all H 6 [CoW 12 O 40 ] RFB. The ion permeability increases while the area specific resistanceas decreases as reducing the membrane thickness. As a result, the RFB with N211 membrane exhibits best comprehensive performance, which exhibites the energy efficiency of 88.6% at current density of 0.10 A cm −2 and the power density of 0.56 W cm −2  at 0.60 A cm −2 . Moreover, the battery delivers impressive cycling performance of 100 cycles with an average coulombic efficiency of 99.4%, energy efficiency of 80.0%, and capacity retention of 99.98% per cycle at current density of 0.20 A cm −2 . [ABSTRACT FROM AUTHOR]

An accurate prediction of ion selective adsorption in ion exchange membranes is essential to reflect the role of fixed charges on ion transport through the membrane in vanadium redox flow batteries (VRFB). Unlike those empirical models reported in the literature, this work reports on a new ion selective adsorption model with the Donnan effect considered for movable ions distributed in the membrane pores only. This model, no longer relying on empirical coefficients, is then applied to the calculation of ion transport through membranes in VRFBs. The model shows a more accurate prediction of vanadium crossover and membrane conductivity, and enables to capture the effect of key membrane properties on battery performance. It is found that (i) an increase in H 2 SO 4 concentration reduces the electrolyte imbalance and improves the coulombic efficiency; (ii) an increase in membrane porosity significantly improves the membrane effective conductivity; (iii) the change of fixed charges should be careful to balance all performances. Therefore, membrane properties and operating conditions need proper adjustment to improve the battery performance, and our VRFB model is a good tool to help membrane optimization. [ABSTRACT FROM AUTHOR]

A modified membrane for vanadium redox flow battery (VRFB) was prepared by grafting sodium 4-styrenesulfonate (NaSS) to the surface of Nafion 212 via the oxygen plasma induced grafting technique to reduce the crossover of vanadium ions of the membrane. By grafting with poly(styrenesulfonic acid) (PSS), the crossover of vanadium ions through the Nafion membrane is only 32% of that of the pristine Nafion membrane. Thus, comparing with pristine Nafion membrane, the resulting Nafion- g -PSS membrane exhibits higher ion exchange capacity (IEC) and through-plane conductivity. In addition, this Nafion- g -PSS membrane improves the voltage efficiency (VE), coulombic efficiency (CE), and energy efficiency (EE) of VRFB. Owing to lower vanadium ions permeability, the VRFB with Nafion- g -PSS membrane exhibited much slower self-discharge than the VRFB with pristine Nafion 212, and the VE, CE, and EE after 200 cycles of charge-discharge test remain stable. In particular, the VRFB with Nafion- g -PSS membrane exhibits higher capacity retention than the VRFB with pristine Nafion 212 membrane. [ABSTRACT FROM AUTHOR]

It is important to measure in-plane conductivity of Nafion membrane for fuel cell, but this target is generally inhibited by measuring system with heterogeneous interfaces and immature electrochemical measurements. This paper simply used water media to establish stable measuring system with metal electrode and Nafion membrane, representing system as equivalent circuit. Our equivalent circuit was validated by both cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements, also clarified connection and difference in two measurements. This electrochemistry breakthrough helps realize measuring system completely and reliably even under successive temperature cycles, providing circuit elements for kinetic analysis in contact resistance, in-plane conductivity, inactive and active proton. We also clarified that the inactive and active proton shift can dictate low frequency inductance, which is an important sign for active and stable operation in fuel cell, secondary battery and materials. All these results can induce enormous progress in multi-disciplines, making our work have great significance and broad impact for future studies. • The equivalent circuit is key for measurements and analysis. • The equivalent circuit was validated by EIS and CV measurements. • The equivalent circuit has good in situ characterization for measuring system. • The circuit elements revealed kinetic relationship for measuring system. [ABSTRACT FROM AUTHOR]

• The thermal conductivity of Nafion membranes is dominant affected by water content. • The hydrogen bonds network is the dominant factor affecting thermal conductivity. • There are two significant ways to improve interchain heat transport by hydrogen bonds. • A well-established thermal network is formed when water content is more than 15. • Hydration level influences the effect of temperature on the thermal conductivity. The thermal conductivity of the proton exchange membrane significantly affects the operating performance of the fuel cell. In this work, the impact of water content and temperature on thermal conductivity of hydrated Nafion membranes was investigated via molecular dynamics simulations and the influencing mechanism was explained from the perspective of interchain and intrachain heat transfer. The study shows that the thermal conductivity is mainly positively affected by water content, which is a result of the triple effect of hydrogen bonding acting as interchain heat transfer bridge, the stronger microphase separation allowing water to behave more like bulk water, and the decrease in the degree of chain torsion resulting in less phonon scattering along the chain. Particularly, we emphasized two crucial paths in which hydrogen bonding improves interchain heat transport. Furthermore, the temperature has little and slightly negative effects on thermal conductivity at low and high hydration levels, respectively. That is because, in low hydration levels, the incomplete hydrogen bond network is hardly influenced, but the bridging effect is suppressed and intrachain heat transfer capacity is reduced in high hydration levels. We believe this study can broaden the design basis of high temperature polymer electrolyte membranes. [Display omitted] [ABSTRACT FROM AUTHOR]

Despite the extensive attention that water transport in Nafion membranes has been subject to, several phenomenal still remain unexplained. It is for instance not clear why desorption rate is much faster than absorption. The purpose of this paper is to suggest an answer to that problem. A simple but thermodynamically consistent model is formulated within the framework of Classical Irreversible Thermodynamics including swelling and interaction of the membrane with the surrounding water vapor. Numerical solutions to the model are in a good match with experimental data of sorption dynamics. By simplifying the model (excluding swelling and assuming instantaneous diffusion within the membrane), we are able to identify the source of the asymmetry between the absorption and desorption rates - the shape of the uptake curve. This natural explanation of the asymmetry is then discussed quantitatively (showing an agreement between both the full and the simplified model but also with the experimental data) and also in the context of active carbon sorption. [ABSTRACT FROM AUTHOR]

The triode operation of humidified PEM fuel cells has been investigated both with pure H 2 and with CO poisoned H 2 feed over commercial Vulcan supported Pt(30%)-Ru(15%) anodes. It was found that triode operation, which involves the use of a third, auxiliary, electrode, leads to up to 400% power output increase with the same CO poisoned H 2 gas feed. At low current densities, the power increase is accompanied by an increase in overall thermodynamic efficiency. A mathematical model, based on Kirchhoff’s laws, has been developed which is in reasonably good agreement with the experimental results. In order to gain some additional insight into the mechanism of triode operation, the model has been also extended to describe the potential distribution inside the Nafion membrane via the numerical solution of the Nernst-Planck equation. Both model and experiment have shown the critical role of minimizing the auxiliary-anode or auxiliary-cathode resistance, and this has led to improved comb-shaped anode or cathode electrode geometries. [ABSTRACT FROM AUTHOR]

The durability of a proton exchange membrane is affected by both mechanical degradation and chemical degradation. While fatigue and relative humidity cycling tests have been conducted to address mechanical degradation, the cyclic behavior that bridges the gap between the stress-strain response and fatigue behavior is not well established. The objective of this study is to understand the strain evolution during biaxial cyclic loading that resemble the actual stress state of the membrane. In particular, the effect of loading paths on strain evolution is examined to account for the stress state on strain accumulation. It is found that the constraint effect of stress in one direction on strain evolution in another direction strongly depends on the stress state of the membrane, and the equibiaxial stress state imposes the most significant constraint on strain evolution. Furthermore, the constraint effect induced by biaxial loading is more significant at higher relative humidity values. Moreover, high-stress amplitude cycle acts to retard strain accumulation in the subsequent low-stress amplitude cycle. The findings reported here will provide new evidence for an understanding of the fatigue behavior of a proton exchange membrane as well as durability modeling of proton exchange membrane fuel cells. [ABSTRACT FROM AUTHOR]

Nafion membranes plasticized with dimethyl sulfoxide (DMSO) have been examined at room temperature using the vacuum ATR - FTIR spectroscopic technique in the range 50–4000 cm − 1 . The amount of the plasticizer corresponds to the molecular ratio n = DMSO/H + = 1.2, 2.3, 4.8, 7.0, 9.7 and 13.3. The medium intensity band with two maxima at 780 and 853 cm − 1 have been assigned to the ν (SO) stretching vibrations of the H + (DMSO) 2 complex. The possible reason of ν (SO) splitting is symmetry decrease of hydrogen bond under the influence of the anion group SO 3 − electric field. Whereas the mutual association of free DMSO molecules in Nafion leads to appearance of weak band at 86 cm − 1 assigned to the dipole-dipole interactions. [ABSTRACT FROM AUTHOR]

The possibility to perform chemical reactions inside polymer materials opens a unique opportunity to control and prepare materials for diverse solid-state applications. Based on the affinity of Eu 3+ ions for oxygen functionalities, in this work we report the luminescence enhancement of Eu 3+ ions inserted in Nafion membranes (Naf/Eu 3+ ) by in-situ complexing to oxalate. The formation of a europium-oxalate type complex enhances Eu 3+ luminescence emission, which could be exploited for the construction of devices for oxalate sensing and the fabrication of highly luminescent materials. Possible analytical applications of Naf/Eu 3+ membranes were evaluated by fluorescence spectroscopy through the linear response with concentration. The complex formation was followed by infrared spectroscopy and SEM-EDS analysis. [ABSTRACT FROM AUTHOR]

In this paper, a novel amperometric CO sensor using Nafion and Pt/C composite electrodes was fabricated. Three kinds of carbon materials (carbon fibers, multiwall carbon nanotubes and carbon blacks) were utilized as the supports of the sensing and reference electrodes for the CO sensors. The results revealed that the effective Pt loadings on the electrodes increased in the following order: carbon fibers (CFs) > multiwall carbon nanotubes (MWCNTs) > carbon blacks (CBs), leading to the increasing of the sensitivities toward CO in same order. In other words, the sensor using Pt/CFs as the sensing electrode (SE) showed the highest sensitivity with the value of 0.077 μA/ppm and shortest response time in the range of CO concentration from 1 to 200 ppm at room temperature. Further, a reproducible and stable response against 50 ppm CO was obtained for the sensor with Pt/CFs SE materials. Moreover, a low detection limit of 0.1 ppm for CO was also examined, suggesting that the sensor can be convenient for detecting very low traces of CO. [ABSTRACT FROM AUTHOR]

Zirconium dioxide (ZrO 2 ) nanoparticles were fabricated successfully via ultrasonic-assisted method using ZrO(NO 3 ) 2 ·H 2 O, ethylenediamine and hydrazine as precursors in aqueous solution. Morphology, structure and composition of the obtained products were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), dynamic light scattering (DLS), Fourier transform infrared spectroscopy (FT-IR) and diffuse reflectance spectroscopy (DRS). Then, the synthesized nanoparticles were used to prepare Nafion/ZrO 2 nanocomposite membranes. The properties of the membranes were studied by ion exchange capacity (IEC) proton conductivity (σ), thermal stability and water uptake measurements. The ex-situ Fenton’s test was used to investigate the chemical stability of the membranes. From our results, compared with Nafion membrane, the nanocomposite membrane exhibited lower fluoride release and weight loss. Therefore, it can concluded that Nafion/ZrO 2 nanocomposite exhibit more chemical stability than the pure Nafion membrane. ATR-FTIR spectra and SEM surface images of membranes also confirm these results. [ABSTRACT FROM AUTHOR]

We report a pervaporation process to remove water from a solution containing ionic liquid (IL) + solvent + water. Specifically, Nafion-based membranes were employed for the separation, and tributylmethylammonium dimethylphosphate and N-methyl-2-pyrrolidone (NMP) were the IL and solvent, respectively. Membrane swelling in contact with the IL–NMP–H2O solution was accommodated by judicious use of gaskets and membrane supports. The pervaporation fluxes of water and NMP increased with temperature and flow rate of the permeate sweep gas. Among the membranes examined, a commercially available Nafion membrane (XL, Ion Power) provided the highest water (10 mg h−1cm−2) and NMP (182 mg h−1cm−2) fluxes. The results show that pervaporation separation is a technologically feasible method to decrease the water content of an IL–NMP–H2O solution from 1 to 0.5 wt%. [ABSTRACT FROM AUTHOR]

Direct alcohol fuel cells (DAFCs) have attracted considerable attention recently as alternative energy resources due to their high efficiency compared with other types of fuel cells. Currently, the two most common types of DAFCs are direct methanol fuel cells (DMFCs) and direct ethanol fuel cells (DEFCs), which use methanol and ethanol solutions as fuel, respectively. The most widely used polymer membrane for DAFCs is Nafion because it exhibits superior proton conductivity and excellent mechanical properties and chemical stability. However, Nafion membranes for DAFCs are expensive, have limited device lifetimes due to chemical and mechanical degradation, and have higher fuel crossovers through the membrane. Typically, to improve Nafion membranes, many researchers have modified Nafion membranes by modifying the Nafion matrix with organic or inorganic materials with different structures, sizes and compositions, modification techniques, or multilayered systems in order to improve the physical properties of Nafion. The characterization, properties, and performance of DAFCs from various types of modified Nafion membranes are critically reviewed by giving detailed examples. The challenges and future prospects for the modification of Nafion membranes for DAFC applications are also discussed. [ABSTRACT FROM AUTHOR]

A fuel-cell-type gas sensor based on the membrane electrode assemble (MEA) composed of proton exchange membrane (Nafion) and Pt/C sensing electrodes was fabricated for detection of CO at room temperature. The Pt/C electrodes materials were synthesized from Vulcan XC-72 carbon powders and hexachloroplatinic acid (H 2 PtCl 6 ). This paper mainly focused on the effect of various dispersants (ethylene glycol (EG) tetraethyl orthosilicate (TEOS), glycerol and EG/polytetrafluoro-ethylene (PTFE)) on the performance of the presented sensor. Results revealed that the sensor utilizing EG as the dispersant elicited the highest response current toward 50 ppm CO. The current of the sensor was linearly correlated with CO concentration in the range of 1–200 ppm, which sensitivity was 88 nA/ppm. In addition, the 90% response and recovery times of the sensor toward 50 ppm CO were 22 and 24 s, respectively. Besides, the prepared CO sensor also had a good repeatability and acceptable selectivity. [ABSTRACT FROM AUTHOR]

Proton conductivity of Nafion membranes, the key feature for their application in proton exchange membrane fuel cells, has been reported in many works. It becomes necessary to assemble these massive reports to present an overview for further development guidelines. We apply an exhaustive search and retrieve 3539 records from 310 original reports. These records are dumped into a database and a statistical analysis is carried out to establish the overview. The histogram, the trend, the temperature, the relative humidity and fillers related to the proton conductivity of Nafion membranes are investigated. There is not always positive progress in recent 13 years to improve the proton conductivity of Nafion membranes. The proton conductivity can be fitted using a simple exponentially increasing function for relative humidity dependence, and the Arrhenius equation for temperature dependence with acceptable correlation confidence. Water contents in membranes from vapor can be well depicted by Brunauer–Emmett–Teller equation, and they have reasonable correlation with proton conductivities. Inorganic fillers usually provide better enhancement in proton conductivity than organic fillers, which is a result of the former have better water-holding capability. Fillers that can facilitate the formation of percolated water channel with less tortuosity have high probability to significantly improve the proton conductivity of Nafion membranes. [ABSTRACT FROM AUTHOR]

Water transport during sorption and desorption in Nafion ® 117 samples is studied by means of dynamic model and experiments as a response of relative humidity step. The model takes into account a transfer resistance at the interface between the membrane and the surrounding medium, and considers that the water content of the membrane remains uniform at all times during sorption and desorption, which was confirmed using NMR imaging. Thus, its main hypothesis is that the membrane is in equilibrium with the humid gas located at the interface whose relative humidity is different than in the bulk. The calculated time-variations in the water content of a membrane sample (in acid form) during sorption and desorption show that desorption is faster than sorption due to the variations in the slope of the water uptake isotherm. The theoretical results and the experimental data show a good agreement which allows the determination of the mass transfer coefficient. The influence of diffusion and thermal effects are also discussed. [ABSTRACT FROM AUTHOR]

The water distribution of a Nafion-based membrane in a direct methanol fuel cell was analyzed in-operando using high resolved synchrotron X-ray radiography. A specially developed fuel cell design that meets the requirements for radiography as well as for stable cell operation was used. Different electric loads were applied during cell operation. A correlation between the electric load of the cell and the thickness of the membrane was found: the membrane thickness increased with increasing current density. The impact of local water drop dynamics on the water distribution in the membrane and the electrodes have been analyzed. We found a strong influence of water drops in the cathode channel on the water distribution in the adjacent area of the Nafion membrane. [ABSTRACT FROM AUTHOR]

The effect of various system parameters such as wastewater Chemical Oxygen Demand (COD) concentration, pH, conductivity, membrane size and thickness on efficient energy production using mixed isolated culture from the distillery wastewater in the MFC was studied. The power density increased with increase in the anolyte pH from 6 to 8. The peak power density and COD removal efficiency was observed as 63.8 ± 0.65 mW/m 2 and 63.5 ± 1.5% at pH 8, respectively. The MFC performance increased with increasing COD concentration (800–3200 mg/l), conductivity (1.1–9.7 mS/cm) and membrane area (8–24 cm 2 ). The MFC operating with wastewater COD concentration of 3200 mg/l and its conductivity of 9.7 mS/cm produced the highest power density of 202 ± 6 mW/m 2 with a corresponding current density of 412 ± 12 mA/m 2 . The results showed that the efficient electricity generation and simultaneous treatment of distillery wastewater can be attained in the MFC. [ABSTRACT FROM AUTHOR]

The polymer cation exchange membrane (Nafion117) was equilibrated garden soil leachate. It was then characterised using the stationary voltamperometry method and the mass transfer electrochemical Hittorf-based method. The results obtained with these two techniques were compared to those obtained with the membrane conditioned only with conventional acid and/or salt electrolytes solutions. These two conditions highlighted the good proton conduction of the membrane, against metal ions. This finding was supported and complemented by impedance spectroscopic studies at both transient and stationary regimes. The parameters studied were electrical impedance and specific conductivity. It was found that at higher frequencies, the conductivity of the membrane conditioned with protons was five times higher than that stored in distilled water. As an application, the membrane was tested successfully in a garden soil microbial fuel cell under study, thereby evidencing its good proton conduction. Nafion exhibits, therefore, a high protonic conductivity when hydrated, because protons can be transported via Grotthus and hopping mechanisms via its functional sites. [ABSTRACT FROM AUTHOR]

• Sulfur-doped TiO 2 greatly affected characteristics of laccase-modified electrodes. • The nanoparticles and enzyme were immobilized at a carbon electrode using a Nafion film. • The formed biosensor membranes were studied by positron annihilation spectroscopy. • The nanomodified bioelectrodes were tested for phenol analysis in wastewater. The search for new nanoscale materials with predictable properties to target the timely and fast detection of toxic components in wastewater is one of the most promising directions of modern biosensorics. We have shown that TiO 2 nanoparticles modified with sulfur significantly improve the main operational parameters of laccase-based electrodes when compared with controls. The nanoparticle samples were labeled as TiO 2 S(0.75), TiO 2 S(1.5), and TiO 2 S(3.0), in which the numbers in parentheses refer to the quantity of H 2 SO 4 (mL) used in the synthesis. The nanoparticles and enzyme were immobilized by means of Nafion film formed on a carbon rod electrode. It was shown that the modification of Nafion film by TiO 2 or TiO 2 S(1.5) nanoparticles does not affect the size of the nanocavities and defect structure of the main polymer matrix as revealed by positron annihilation spectroscopy. It testifies that the structural-morphological difference between the film samples is rather small, and the improving of the sensor operational parameters for TiO 2 S(1.5)-based laccase electrodes is connected only with the impact of sulfur doping, but not the difference in membrane properties. The developed bioelectrodes were tested for phenol analysis in real communal wastewater samples spiked with these analytes, demonstrating the high accuracy of the assay. [ABSTRACT FROM AUTHOR]

Foreign cations have detrimental effects on the transport performance of polymer electrolyte membranes. In this study, the effects of two typical kinds of cations (Na+ and Ca2+) on the diffusion of hydronium ions (H 3 O+) and water molecules (H 2 O) in Nafion 117 membranes are investigated using molecular dynamics simulations, at the same time the effects of temperature are considered. The mechanisms of effects are analyzed using radial distribution functions, water clusters distribution and relative concentration distribution. Results show that the diffusion coefficients of H 3 O+ and H 2 O are significantly reduced by the presence of Na+ and Ca2+. Moreover, the impact of Ca2+ is more serious. Further investigations show that cations affect intramembrane transport properties by occupying sulfonic groups and disrupting the connectivity of water clusters. The difference in the effects of these two kinds of cations is discussed by hydrated radius, hydration degree of cations, and the interaction between cations and sulfonic groups. Increasing temperature can increase not only the diffusion coefficients, but also interaction between the cations and the sulfonic groups. However, the interaction between the sulfonic groups and H 2 O is decreased by the increasing temperature. • Transport performance of Nafion is decreased by cations. • The connectivity of water clusters is severely damaged. • Increasing temperature has different effects on the interaction between particles. [ABSTRACT FROM AUTHOR]

Several degradation processes limit the lifetime of polymer electrolyte membranes in fuel cells. One of these processes is humidity changes during the operation of the cell, which causes swelling and shrinking of the polymer electrolyte membrane. Changes in membrane size lead to periodic mechanical stresses, which damage the polymer. This damage leads to the formation of cracks in the membrane and, thus, results in early failure of the fuel cell. This study presents a theoretical model that predicts the membrane lifetime depending on the thickness of the membrane and operating conditions of the periodic humidity cycle such as: amplitude of the humidity variation in the cycle, cycle duration, and temperature. The model is based on the assumption that mechanical destruction of the polymer electrolyte membrane, constrained in the fuel cell, occurs when the deformation energy applied to the membrane reaches a maximum value. The mechanical stress and deformation energy are estimated using the modified Eyring equation [Burlatsky et al., 2012]. The proposed model takes into account the influence of the temperature and water concentration on the membrane mechanical properties. The water concentration in the membrane is simulated by considering the water sorption/desorption kinetics and water sorption isotherm of the membrane. The model was used to predict the lifetime of the non-reinforced membrane Nafion. The calculation results show that membrane mechanical durability correlates positively with increasing membrane thickness and temperature. The increase in the amplitude of the humidity cycle decreases membrane mechanical durability. At very short humidity cycles (≤50−100  s ), the membrane lifetime declines with increasing period of the humidity cycle. At higher humidity cycle period (>50−100  s ), the increase of the cycle duration leads to continuous growth of the membrane lifetime. [ABSTRACT FROM AUTHOR]

Sponge-Nafion membranes were prepared by electro-spinning (ES) method and with polyacrylonitrile (PAN) or polyvinylpyrrolidone (PVP) as additives. First the optimum conditions of ES were achieved to prepare Nafion membranes with sponge-like structure. Then the membranes were further processed by electrostatic spray method to enhance their properties. SEM, IR were used to characterize the morphologies and structure. Proton conductivity was measured by the CHI66C electrochemical workstation (Shanghai Chen Hua Instrument Company). Results showed that the sponge-Nafion membranes possessed better proton conductivity especially at relatively high temperatures than that of commercial Nafion membranes. [ABSTRACT FROM PUBLISHER]

Epistemic uncertainty, whether due to lack of knowledge or data, is often prevalent in practical engineering structures. We present an effective uncertainty quantification method based on orthogonal experimental design, range analysis and interval analysis for analyzing and propagating this type of uncertainty. Orthogonal experimental design and range analysis are first used to investigate the effect of epistemic uncertain factors on different metrics (such as minimum computational cost, maximum computational accuracy and a mixture of two). Interval analysis is then employed to propagate the dominant epistemic uncertainty from input to output through a model. The present method is applied to construct a uniaxial tension model of polymer Nafion membrane with four selected epistemic uncertain factors (mesh method, element type, boundary condition and constitutive model). A good understanding of the influence of these factors on the outputs of the constructed model demonstrates the effectiveness of the present method. [ABSTRACT FROM AUTHOR]

The membrane is often considered as the heart of the proton exchange membrane fuel cell (PEMFC), and it is of pivotal importance for the involved transport phenomena and performance of the entire PEMFC. The Nafion® membrane is the most commonly used type of membrane in PEMFCs. In this paper, the nano-scale structure of the Nafion® membrane is reconstructed using dissipative particle dynamics. The average water pore sizes of the equilibrated membranes are estimated by employing the radial distribution function, and the reconstructed nano-scale membranes are then used to evaluate water diffusion within the membrane by calculating the mean square displacement. The tortuosity of the membrane is evaluated by comparing the diffusivity of the membrane to that of a limiting case of cylindrical channels. Important findings from this study are presented by the membrane structures, water diffusivity at different water saturations, and calculations of the tortuosity within the membrane. [ABSTRACT FROM AUTHOR]