Modification of Nafion membrane using poly(4‐vinyl pyridine) for direct methanol fuel cell

Perfluorinated membrane such as Nafion (from Du‐Pont) has been used as a polymer electrolyte membrane. Nafion 117 membrane, which was usually used as the electrolyte membrane for the polymer electrolyte membrane fuel cell (PEMFC), was modified by using poly(4‐vinyl pyridine) (P4VP) to reduce the methanol crossover, which cause fuel losses and lower power efficiency, by the formation of an ionic crosslink structure (sulfonic acid‐pyridine complex) on the Nafion 117 surface. Nafion film was immersed in P4VP/N‐methyl pyrrolidone (NMP) solution. P4VP weight percent of modified membrane was controlled by changing the concentration of P4VP/NMP solution and the dipping time. P4VP weight percent increased with increasing concentration of dipping solution and dipping time. The thickness of the P4VP layer increased with increasing concentration of dipping solution and dipping time when the concentration of the dipping solution was low. At high P4VP concentration, the thickness of the P4VP layer was almost constant owing to the formation of acid–base complex which interrupted the penetration of P4VP. FTIR results showed that P4VP could penetrate up to 30 µm of Nafion 117 membrane. Proton conductivity and methanol permeability of modified membrane were lower than those of Nafion 117. Both decreased with increasing concentration of dipping solution and dipping time. Methanol permeability was observed to be more dependent on the penetration depth of P4VP. Water uptake of the modified membrane, the important factor in a fuel cell, was lower than that of Nafion 117. Water uptake also decreased with increasing of P4VP weight. On the basis of this study, the thinner the P4VP layer on the Nafion 117 membrane, the higher was the proton conductivity. Methanol permeability decreased exponentially as a function of P4VP weight percent. Copyright © 2006 Society of Chemical Industry     

Prediction of methanol and water fluxes through a direct methanol fuel cell polymer electrolyte membrane

Development of a direct methanol fuel cell (DMFC) mass flux model, using conventional transport theory, is presented and used to predict the fluid phase superficial velocity, methanol and water molar fluxes, and the chemical species (methanol and water) dimensionless concentration profiles in the polymer electrolyte membrane, Nafion^® 117, of a DMFC. Implementation of these equations is illustrated to generate the numerical data as functions of the variables such as the pressure difference across the membrane, methanol concentration at the cell anode, temperature, and position in the membrane.     

聚二甲基硅氧烷膜中乙醇-水的吸附和渗透蒸发行为

以乙醇/水体系为研究对象,结合F lory-Huggins理论,讨论溶胀过程的热力学行为,用以分析和考察聚二甲基硅氧烷(PDMS)膜在乙醇/水中的溶胀特性及组分间的耦合效应。结果表明,在乙醇质量分数20%—40%,膜的溶胀程度最大。渗透蒸发实验表明,水的渗透速率在乙醇质量分数不大于30%范围内变化很小,而乙醇的渗透速率基本随溶液中乙醇质量分数增加而增大。     

The sorption and permeation of co2 and ch4 for dimethylated polysulfone membrane

The sorption and permeation properties of the CO₂ and CH₄ were measured for polysulfone and dimethylated polysulfone to investigate the structure-property relationships. The effect of operating pressure on the transport properties of the polysulfones was examined. The permeation properties for a mixture of CO₂ and CH₄ (CO₂/CH₄=57.5/42.5 vol%) were also measured and these results were compared with those obtained from the experiments of pure gases. The sorptions of CO₂ and CH₄ are well described by“dual-sorption model”. The permeability coefficients of CO₂ and CH₄ decreases with increasing upstream pressure, as is often the case with other glassy polymers. The permeability coefficients of each gas of binary mixture are reduced than those for pure gases. This result is due to the competition of each gas for the Langmuir sites. The free volume of the dimethylated polysulfone is lower than that of polysulfone, and dimethylated polysulfone shows relatively lower permeability coefficients and higher selectivity than polysulfone.     

Adsorption of some heavy metal ions from aqueous solutions on Nafion 117 membrane

Nafion 117 membrane was investigated for the removal of Ni(II), Co(II), Pb(II), Cu(II) and Ag(I) metal ions from their synthesized aqueous solutions. The different variables affecting the adsorption capacity of the membrane such as contact time, initial metal ion concentration in the feed solution, pH of the sorption medium and temperature of the solution were investigated on a batch sorption basis. The affinity of Nafion 117 membrane towards heavy metal ions was found to increase in the sequence of Cu(II), Ni(II), Co(II), Pb(II), and Ag(I) with adsorption equilibrium achieved after 30 min for all metal ions. Among all parameters, pH has the most significant effect on the adsorption capacity, particularly in the range of 3.1-5.9. The variation of temperature in the range of 25-65 °C was found to have no significant effect on the adsorption capacity. Nafion 117 membrane was found to have high stability combined with repeated regeneration ability and can be suggested for effective removal of heavy metal ions such as Cu(II), Ni(II) and Co(II) from aqueous solutions.     

Water vapor permeation and compressed air dehydration performances of modified polyimide membrane

In this paper, modification of polyimide hollow fiber membrane was carried out by introduction of tetrabutylammonium naphthalenesulfonate (BAN) into the membrane matrix. Permeation performance of modified hollow fibers was investigated helps to compressed air dehydration ability across the membrane. The experimental results showed that water sorption and water vapor permeability obviously increase with increase on BAN content in modified membranes, and air dehydration performance was improved by increasing BAN in membrane and ratio of sweeping gas. Moreover, operational pressure and feed flux also impose on important effect on compressed air dehydration capability.     

Sorption, diffusion, and permeation of light olefins in poly(ether block amide) membranes

Sorption, diffusion, and permeation of three olefins (i.e., C₂H₄, C₃H₆, and C₄H₈) in poly(ether block amide) (PEBA 2533) membranes at different temperatures and pressures were investigated. This is pertinent to olefin recovery from resin off gas in polyolefin manufacturing. The relative contribution of solubility and diffusivity to the preferential permeability of olefins over nitrogen was elucidated. It was revealed that the favorable olefin/nitrogen permselectivity was primarily attributed to the solubility selectivity, whereas the diffusivity selectivity may affect the permselectivity negatively or positively, depending on the operating temperature and pressure. The olefin permeability is in the order of C₄H₈>C₃H₆>C₂H₄, the same order as their solubility in the membrane. In general, a low temperature favors both the permeability and selectivity. With an increase in pressure and/or a decrease in temperature, the sorption uptake of the olefin in the membrane increases progressively, and the diffusivity and hence the permeability are also enhanced because of the increased membrane plasticization/swelling caused by the penetrant sorbed in the membrane. At a given temperature, the pressure dependence of solubility and permeability could be described empirically by an exponential function. The limiting solubility at infinite dilution was correlated with the reduced temperature, and the hypothetical diffusivity at zero pressure was related to temperature by the Arrhenius equation.     

Nafion膜内基团与水分子的相互作用

Nafion膜由于其良好的电化学性能被广泛应用,但其溶胀性即膜内水分子的存在和含量的大小对膜的性能产生影响,因为水分子会与膜基团发生作用.在制取几种不同端基的Nafion膜的基础上,应用红外光谱方法比较膜的不同基团对水分子结构对称性的不同影响,从而探讨基团与水分子的作用方式.膜内的阳离子Lewis酸性越强,对-OH的亲和性越强,水分子不对称性越大,其O-H伸缩振动越困难,振动频率越大,强度越强;膜内的阴离子,Lewis碱性越强,水分子O-H伸缩振动越困难,频率越大,基团的这种效应与溶液中氢键的作用相反.     

Modification of Nafion membranes by incorporation of cationic polymers for reduction of methanol permeability

A small amount of basic polymer was incorporated in the Nafion membrane. Compared with the re-cast Nafion membrane, the Nafion/basic polymer membrane reduced the methanol permeability considerably. The equilibrium water uptake and proton conductivity decreased, but the thermal and mechanical stability was enhanced with increasing concentration of basic polymer. These property changes were caused by formation of cation/anion complex between acidic Nafion and basic polymer molecules. The effects of the types and molecular weights of basic polymers on the methanol permeability and proton conductivity were not significant.     

Pervaporation removal of water from ionic liquid solutions using Nafion membranes

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^?1 cm^?2) and NMP (182 mg h^?1 cm^?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%.     

Influence of ligands of palladium complexes on palladium/Nafion composite membranes for direct methanol fuel cells by supercritical CO2 impregnation method

Palladium/Nafion composite membranes were synthesized by supercritical impregnation method to reduce methanol crossover in direct methanol fuel cells. The palladium complexes used in this study were palladium(II) acetylacetonate, palladium(II) hexafluoroacetylacetonate, and palladium (II) bis(2,2,6,6-tetramethyl-3,5-heptane-dionato). The palladium complexes with various loading amounts from 0.010 to 0.050 g in a high-pressure vessel were dissolved in supercritical CO₂, and impregnated into Nafion membranes.The SEM images indicated that the palladium complexes were successfully deposited into Nafion membrane, and there were no problems such as cracking and pinhole. The EDX analysis showed that the palladium particles were distributed both at the membrane surface and also extended deeper into the membrane. The TEM images indicated that thin dense band of agglomerated Pd particles can be observed near the membrane surface, and a significant number of isolated Pd particles can be seen deeper into the membrane, when Pd(II) acetylacetonate was used as palladium complex. When palladium(II) hexafluoroacetylacetonate and palladium (II) bis(2,2,6,6-tetramethyl-3,5-heptane-dionato) were used, dense band of agglomerated Pd particles cannot be observed near the membrane surface, and small Pd particles were observed inside the membranes.The XRD analysis indicated that the crystalline peak of Nafion membrane at 2θ = 17° increased with the supercritical CO₂ treatment. It means that the degree of crystallinity for Nafion membrane increased by supercritical CO₂. The metal Pd peak at 2θ = 40° was observed for the Pd/Nafion membranes.The methanol crossover was reduced and the DMFC performance was improved for the Pd/Nafion membranes compared with Nafion membrane at 40 °C. The successful preparation of Pd/Nafion membranes by supercritical CO₂ demonstrated an effective alternative way for modifying membranes and for depositing electrode catalytic nanoparticles onto electrolyte.     

Interaction of dimethyl methylphosphonate with Nafion in acid and cation modifications

Sorption kinetics and sorption isotherms have been determined for dimethyl methylphosphonate, DMMP, in a perfluoroionomer, Nafion™, in the acid form and as calcium and ferric salts. Nafion is a phase segregated polymer with a fluorocarbon main chain and sulfonic acid terminated fluoroether side chain comprising 33 wt% of the polymer. DMMP swells only the fluoroether region. Under immersion conditions, equilibrium solubilities for all three forms are essentially equal, averaging about 130 wt%. Kinetics are non-Fickian, dominated by relaxation effects, with calcium much slower than the acid form of Nafion, and ferric slower still. Analysis with the Joshi-Astarita model of relaxation coupled diffusion indicates that the effect of cation modification is a more than 200-fold decrease in both diffusion coefficient and relaxation rate. Vapor sorption kinetics is also non-Fickian and dominated by relaxation, frequently involving a series of steps or several maxima at high vapor activity. Additionally, kinetics and, to a lesser extent equilibrium solubilities, are affected by sample history and conditions of sample exposure. The sorption isotherm, for acid Nafion exhibits a rapid concentration increase at vapor activities below 0.2, a low slope at intermediate activities and a rapid increase above activity 0.8. Isotherms for salt modifications are similar but with even lower slope at intermediate activities. Effective diffusion coefficients for acid Nafion, calculated from boundary layer corrected steady state permeabilities combined with the sorption isotherm, exhibit a pronounced rise at a volume fraction of 0.6. A transition in NMR solvent self-diffusion coefficients attributed to the emergence of a new phase segregated structure is reported at the same concentration. When effective diffusion coefficients are converted to solvent self-diffusion coefficients, the values are 30-fold lower than NMR values at low concentrations, taken as a measure of tortuosity, but closely approach NMR values above the transition. The prominence of relaxation controlled sorption kinetics and high degree of tortuosity below the transition suggest that Nafion is a disordered structure of small interspersed fluoroether and fluorocarbon regions, whereas the occurrence of discrete relaxation events, mainly at high activities, is probably associated with larger scale reorganization of the partially coalesced phases above the transition.     

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.     

Plasma modification on a Nafion membrane for direct methanol fuel cell applications

This research focuses on Nafion modification using plasma techniques for direct methanol fuel cell applications. The results indicated the both argon (Ar) and carbon tetrafluoride (CF₄) plasma treatments modified the Nafion surface substantially without altering the bulk properties. The Nafion surface exposed to CF₄ plasma resulted in a more hydrophobic layer and an even lower MeOH permeability than the Ar-treated membrane. The plasma operating conditions using CF₄ were optimized by utilizing an experimental design. The minimum MeOH permeability was reduced by 74%. The conductivity was 1–2×10^-3 S/cm throughout the entire experimental range. Suppressed MeOH permeability can be achieved while maintaining the proton conductivity at a satisfactory level by adjusting the plasma operating conditions.     

Performance comparison of portable direct methanol fuel cell mini-stacks based on a low-cost fluorine-free polymer electrolyte and Nafion membrane

A low-cost fluorine-free proton conducting polymer electrolyte was investigated for application in direct methanol fuel cell (DMFC) mini-stacks. The membrane consisted of a sulfonated polystyrene grafted onto a polyethylene backbone. DMFC operating conditions specifically addressing portable applications, i.e. passive mode, air breathing, high methanol concentration, room temperature, were selected. The device consisted of a passive DMFC monopolar three-cell stack. Two designs for flow-fields/current collectors based on open-flow or grid-like geometry were investigated. An optimization of the mini-stack structure was necessary to improve utilization of the fluorine-free membrane. Titanium-grid current collectors with proper mechanical stiffness allowed a significant increase of the performance by reducing contact resistance even in the case of significant swelling. A single cell maximum power density of about 18 mW cm⁻² was achieved with the fluorine-free membrane at room temperature under passive mode. As a comparison, the performance obtained with Nafion 117 membrane and Ti grids was 31 mW cm⁻². Despite the lower performance, the fluorine-free membrane showed good characteristics for application in portable DMFCs especially with regard to the perspectives of significant cost reduction.     

Viscosities of coal—water—methanol mixtures

A plot of viscosity measurements for coal—water—methanol mixtures vs. percentage methanol in the liquid indicates that the viscosities of both coal—water and coal—alcohol slurries are increased by the addition of the second liquid. The shape of the slurry viscosity curve is very similar, on a greatly exaggerated scale, to the plot of viscosity versus percentage methanol for the pure liquid mixtures. Measurements were made as a part of a test program involving coal—water-methanol fuels. Initial mixtures were 60 wt% Pittsburgh seam coal in liquids composed of varying proportions of water and methanol. Slurries of Montana Rosebud and Texas Lignite coals in water—methanol mixtures also displayed viscosity maxima, but at different fractions of methanol. There was no viscosity peak for 40, 50 or 55% petroleum coke slurries. Slurries of ground glass in water-methanol mixtures were evaluated for comparison and a viscosity maximum was observed, although the peak occurred at a methanol concentration somewhat lower than it occurs in the pure liquid mixture.     

Facilitated oxygen transport through a Nafion membrane containing cobaltporphyrin as a fixed oxygen carrier

A Nafion membrane containing a cobaltporphyrin (CoP) complex as a fixed oxygen carrier was prepared with a view to facilitate oxygen transport through the membrane. The design concept of the CoP-loaded Nafion membrane was based on the CoP's modification to place the CoP complex in a hydrophobic domain of the microphase-separated structure, in order to facilitate the oxygen transport and to maintain proton conductivity. The oxygen permeability through the CoP-loaded Nafion membrane was higher than the nitrogen permeability, and significantly enhanced at relatively-low oxygen pressures of the upstream, indicating that the fixed CoP complex acted as an oxygen hopping site to facilitate the oxygen transport. The oxygen/nitrogen permselectivity increased with the content of CoP in the Nafion membrane. Electrochemical reduction of oxygen at a glassy carbon electrode, modified with a Pt/C catalyst and the CoP-loaded Nafion membrane, provided additional support for the facilitated oxygen transport by the membrane. Increased current for the reduction of oxygen on the modified electrode by loading CoP indicated that the CoP offered the oxygen hopping site in the Nafion membrane.     

Modification of Nafion membranes with ternary composite materials for direct methanol fuel cells

Composite membranes for direct methanol fuel cells (DMFCs) were prepared by using Nafion115 membrane modification with polyvinyl alcohol (PVA), polyimide (PI) and 8-trimethoxysilylpropyl glycerin ether-1,3,6-pyrenetrisulfonic acid (TSPS). The performance of the composite membranes was evaluated in terms of water sorption, dimensional stability, thermal stability, proton conductivity, methanol permeability and cell performance. The proton conductivity was slightly decreased by 1-3% compared with Nafion115, which still kept the high proton conduction of Nafion115. The methanol permeability of Nafion/PI-PVA-TSPS composite membranes was remarkably reduced by 35-55% compared with Nafion115. The power density of DMFCs with Nafion/PI-PVA-TSPS composite membranes reached to 100 mW/cm², exceeding that with Nafion115 (68m W/cm²).     

聚吡咯修饰Nafion膜直接甲醇燃料电池的性能

用FeCl3化学氧化法制备了PPy/Nafion改性膜,采用浸渍-还原法在PPy/Nafion阴极侧上沉积Co金属,制得Co-PPy/Nafion电解质膜。采用TG、CV及交流阻抗谱测试了Nafion膜及改性膜的热稳定性,质子电导性和甲醇渗透性能,结果表明:PPy/Nafion及Co-PPy/Nafion改性膜具有更好的热稳定性和抗甲醇渗透性。分别以Co-PPy/Nafion改性膜、PPy/Nafion改性膜和纯Nafion膜为电解质膜,PtRu/C为阳极催化剂,Pt/C为阴极催化剂组装DMFC并考察其性能。实验结果表明:Co-PPy/Nafion改性膜组装单电池在高浓度甲醇及大电流密度的测试条件下,表现出更优异的电池性能。     

Nafion 982WX膜的运行特点

介绍了扬农化工集团有限公司6万t/a离子膜烧碱装置的离子膜使用情况,分析了N982WX膜的运行特点。