The effect of corrugated membranes on salt splitting

An investigation of the electrohydrolysis of sodium sulfate using a corrugated Nafion^® 117 membrane is reported. A comparison of the performance of a flat and corrugated Nafion^® 117 in a two-compartment membrane electrolysis cell is made. Corrugating the membrane increased the active membrane area by 57% compared to the projected area. The effect of flow rate, current density and salt concentration on current efficiencies, transport properties and achievable product concentrations are presented. The results show a large improvement on transport properties, current efficiencies and product formation using corrugated membranes. Corrugated membranes gave an improvement of up to 77% on achievable base concentration and an increase of approximately 22% in current efficiency.     

Salt splitting with radiation grafted PVDF membranes

Sulphonated PVDF cation-exchange membranes have been formulated for the splitting of sodium sulphate by electrohydrolysis. Three membranes with different degree of grafting were tested in a two-compartment membrane cell. The effect of flow rate, current density and salt concentration on the performance of each membrane is described. The different flow conditions in front of the membranes did not significantly affect the current efficiency. Productivity was greater at higher current densities, although a slight decrease in the current efficiency was observed. The SPVDF with a 22.7% degree of grafting performed slightly better than the other cation-exchange membranes. The new materials gave acceptable selectivity; low electrical resistance; and excellent chemical, thermal, and mechanical stability. They resulted in superior performance to the commercially available Nafion® 117, enabling an increase of approximately 20% in current efficiencies and sodium transport rates.     

New ionic polymer–metal composite actuators based on PVDF/PSSA/PVP polymer blend membrane

Ionic polymer–metal composite (IPMC) actuators that display continuously large actuation displacements without back relaxation and with large blocking force at low direct current (DC) voltages are used as biomimetic sensors, actuators and biomedical devices. This article reports the preparation and actuation performance of new IPMC actuators based on the polyvinylidene fluoride (PVDF)/polystyrene sulfonic acid (PSSA)/polyvinyl pyrrolidone (PVP) polymer blend membrane, which requires low voltage DC. The performance results of the proposed IPMC actuators are compared with Nafion‐based IPMC actuators. In the blend membrane, PVDF is the hydrophobic polymer, PSSA is the polyelectrolyte, and PVP is the hydrophilic basic polymer. The proposed IPMC actuators based on the PVDF/PSSA/PVP blend membrane of polymer mixture ratios of 60/15/25 and 50/25/25 gave higher actuation displacement and higher blocking force at low DC voltages than the Nafion‐based IPMC actuator. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Simultaneous Recovery of Nickel and Cobalt from Aqueous Solutions using Complexation-Ultrafiltration Process

Simultaneous recovery of nickel and cobalt from aqueous solutions by complexation-ultrafiltration process with polyethylenimine (PEI) was studied. Experiments were performed as a function of polymer/metal ratio (P/M), solution pH, and ionic strength. Effects of concentration time on metal rejection and membrane flux were also studied. At optimum experimental conditions of pH 6.0 and P/M 5.0, the nickel removal efficiency reaches at 99.9% and cobalt removal efficiency goes to 96.4%. Both nickel and cobalt removal efficiencies decreased as the adding salt concentration increases. During 12 h of the ultrafiltration process, the decline of membrane flux was less than 16% and the removal efficiencies for both nickel and cobalt were kept almost constant. Diafiltration was further performed to regenerate PEI. The removal efficiencies for both metals using recycled PEI were found to be close to those with the original PEI. Results from the two-step process of complexation-UF and decomplexation-UF separation showed that it could be a promising method for simultaneous recovery of nickel and cobalt from aqueous solutions.     

Solution‐blown SPEEK/POSS nanofiber–nafion hybrid composite membranes for direct methanol fuel cells

This study aims to develop novel hybrid composite membranes (NHMs) by impregnating Nafion solution into the porous sulfonated poly(ether ether ketone)/polyhedral oligomeric silsesquioxanes (SPEEK/POSS) nanofibers (NFs). The composite membrane was prepared by solution blowing of a mixture of SPEEK/POSS solution. The characteristics of the SPEEK/POSS NFs and the NHMs, including morphology, thermal stability, and performance of membrane as PEMs, were investigated. The performance of NHMs was compared with that of Nafion117 and SPEEK/Nafion composite membranes. Results showed that the introduction of POSS improved the proton conductivity, water swelling, and methanol permeability of membranes. A maximum proton conductivity of 0.163 S cm^?1 was obtained when the POSS content was 6 wt % at 80°C, which was higher than that of Nafion117 and SPEEK/Nafion. NHMs could be used as proton exchange membranes (PEMs) for fuel cell applications. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42843.     

Partially Sulfonated Poly(1,4‐phenylene ether‐ether‐sulfone) and Poly(vinylidene fluoride) Blend Membranes for Fuel Cells

Blend membranes based on high conductive sulfonated poly(1,4‐phenylene ether‐ether‐sulfone) (SPEES) and poly(vinylidene fluoride) (PVDF) having excellent chemical stability were prepared and characterized for direct methanol fuel cells. The effects of PVDF content on the proton conductivity, water uptake, and chemical stability of SPEES/PVDF blend membranes were investigated. The morphology, miscibility, thermal, and mechanical properties of blend membranes were also studied by means of scanning electron microscopy (SEM), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA) measurements. The blend membrane containing 90 wt.% SPEES (degree of sulfonation – DS = 72%) and 10 wt.% PVDF (M_w = 180,000) exhibits optimum properties among various SPEES72/PVDF membranes. Addition of PVDF enhanced resistance of the SPEES membrane against peroxide radicals and methanol significantly without deterioration of its proton conductivity. It's proton conductivity at 80 °C and 100% relative humidity is higher than Nafion 115 while it's methanol permeability is only half of that of Nafion 115 at 80 °C. The direct methanol fuel cell performance of the SPEES membranes was better than that of Nafion 115 membrane at 80 °C.     

Perfluorosulphonic acid (Nafion) membrane as a separator for an advanced alkaline water electrolyser

Nafion membranes of two different equivalent weights (eq. wt) were evaluated as a separator in an alkaline electrolyser with nickel screen electrodes in both KOH and NaOH electrolytes over the concentration range of 10–30 wt % and at temperatures from 25 to 160° C. For the same current densities, the cell voltage with 30% KOH electrolytes was more than twice that with 30% NaOH. This result correlates with the water content of the membrane which is almost twice as high in NaOH electrolytes. Thinner membranes and membranes of lower equivalent weight give lower cell voltages. Materials and performance considerations indicate that a membrane of 1000 eq. wt is the optimum separator for an alkaline electrolyser. Indications are that LiOH may be an even better electrolyte than NaOH for use with Nafion membranes. Further improvements in performance can be expected by membrane pretreatment such as exposing the membrane to elevated temperature in water. Nafion membranes have excellent physical and mechanical properties in alkaline electrolyte and can be used at temperatures up to 250° C.Work performed under the auspices of the US Department of Energy.     

Recast Nafion‐117 thin film from water solution

Perfluorosulfonated ionomer (PFSI) dispersions in various solvents, usually mixtures of organic compounds and water, were used to prepare the membrane‐electrode system in polymer electrolyte membrane fuel cells (PEMFC), the aim being to increase performance by improving the triple contact of graphite (electron conducting material), Pt (hydrogen dissociation catalyst) and ionomeric membrane (proton conducting). When using PFSI dispersions in water‐organic solvent mixture, care must be taken not to poison the Pt catalyst through organic decomposition products, a consequence of the thermal treatment of the electrode‐polymer system bonded with PFSI dispersion. In the present study some procedures for preparing Nafion water dispersion, starting from a Nafion‐117 membrane, are described. The morphological characteristics of the prepared dispersions were compared with Nafion commercial dispersion (NCD). Moreover, membranes with a thickness of 5–20 μm were prepared and characterised, using both the obtained and the NCD dispersions. The obtained data showed that Nafion water dispersion, which can be used to prepare the membrane/electrode system, results in thin membranes that absorb more water than NCD membranes, and have equal and/or higher proton conduction than the NCD.     

质子传导膜内受限空间离子扩散过程

以具有纳米尺度孔径的聚偏氟乙烯(PVDF)质子传导膜为对象,研究电解质溶液中水合离子在受限空间内的传递行为,证明使用纳米尺度多孔膜代替离子交换膜用于液流电池过程的可行性。利用渗透实验分别研究浓度场、压力场,以及不同渗透压条件下膜中离子扩散和水迁移现象,分析传质行为与膜结构和组成之间的关系。结果表明离子在纳米尺度孔径的PVDF膜中的扩散过程与溶液中类似,表观离子扩散系数不受浓度差推动力的影响;离子交换膜中的表观离子扩散系数随浓度差推动力提高而增加。在渗透压作用下,自制PVDF纳米孔膜的水迁移速率低于Nafion 117膜,水迁移带来的负面影响更小;对于H⁺/VO²⁺的离子选择系数超过300,有效透过H⁺而阻止VO²⁺,适用于全钒液流电池过程。     

Influence of additives on the properties of casting nafion membranes and SO‐based ionic polymer–Metal composite actuators

As a typical smart material, ionic polymer metal composite (IPMC) has a sandwich structure, which consists of a base membrane and two thin metallic electrodes on both sides of the base membrane. The properties of the base membrane, Nafion as the most used base material, strongly affect the performance of IPMC actuator. This paper reports the effects of different additives, such as ethylene glycol (EG), dimethyl sulfoxide (DMSO), N, N′‐dimethyl formamide (DMF), and N‐methyl formamide (NMF), on the performances of the casting membranes and SO‐based IPMC actuators. Studies have shown that the microstructures of the casting membranes with EG and DMSO as additives are more loose and amorphous, leading to higher water contents and thus higher conductivity than those with DMF, NMF, and Nafion 117. Among the casting membrane‐based IPMC actuators, EG‐based IPMC actuator has larger deformation and blocking force, higher strain energy density and conversion efficiency at 2 V DC voltage, whose electromechanical properties are most close to that based on Nafion 117. POLYM. ENG. SCI., 54:818–830, 2014. © 2013 Society of Plastics Engineers     

Nafion/PTFE Composite Membranes for Fuel Cell Applications

The composite membranes were prepared by impregnation of porous poly(tetrafluoroethylene) membranes with a 5 wt% Nafion solution. Scanning electron microscope micrographs of composite membranes show the surface and cross section of poly(tetrafluoroethylene) membranes were covered and filled with Nafion resin. Comparison of physical properties and fuel cell performance of composite membranes with those of Nafion membranes (DuPont Co) is presented. The composite membrane has better thermal stability and gas barrier property but worse ionic conductivity than Nafion membrane. Though the composite membrane has a lower conductivity than Nafion membrane, however, owing to the thinner thickness of composite membrane (in thickness of 20±5µm) than Nafion-115 (in thickness of 125µm) and Nafion-117 (in thickness of 175µm) membranes, the composite membrane has a shorter H⁺ ion transporting pathway and thus a higher conductance (conductance = conductivity/membrane thickness) than Nafion-115 and Nafion-117 membranes. Thus the composite membrane has a better fuel cell performance than Nafion-117 and Nafion-115 membranes. In this report, we show that our composite membrane has a fuel cell performance similar to Nafion-112 membrane (in thickness of 50µm).     

The influence of poly(3,4-ethylenedioxythiophene) modification on the transport properties and fuel cell performance of Nafion-117 membranes

Nafion-117/PEDOT composite membranes were synthesized by in situ chemical polymerization of 3,4-ethylenedioxythiophene (EDOT) using ammonium persulfate as an oxidant. The polymerization of EDOT in Nafion membranes for various EDOT/oxidant treatment sequences was studied for the first time. PEDOT introduction leads to a slight decrease in both the ion-exchange capacity and water uptake of the composite membranes, as well as to an increase in cationic transport. Membranes initially treated with an oxidant exhibit better conductivity and lower hydrogen permeability. The effect of both modification of Nafion-117 membranes by PEDOT and hot-pressing of hydrogen-oxygen membrane-electrode assemblies (MEAs) on the performance of proton-exchange membrane fuel cells was studied. The maximum power density of the fabricated MEAs increases 1.5-fold: from 510 (for a pristine Nafion-117 membrane) to 810 mW cm⁻² (for a membrane modified by PEDOT). The current density at a voltage of 0.4 V reaches 1248 and 2246 mA cm⁻², respectively.     

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。     

铸膜液的粘度和组成对PVDF微孔膜性能的影响

实验采用浸没沉淀相转化的方法制备PVDF微孔膜,考察了聚偏氟乙烯(PVDF)/聚乙二醇(PEG-6000)/二甲基乙酰胺(DMAc)比例的变化,对铸膜液的粘度及膜性能的影响。分析了影响膜过程动力学因素,确定了该体系制膜的理想条件。结果表明,当PVDF质量分数为14%,PEG(6000)质量分数为5%时,制得的平板膜可达较佳性能。     

Application of sodium conducting membranes in direct methanol alkaline fuel cells

A study of a direct methanol alkaline fuel cell (DMAFC) operating with sodium conducting membranes is reported. Evaluation of the fuel cell was performed using membrane electrode assemblies incorporating carbon supported platinum catalysts and Nafion^® 117 and 112 membranes. A membrane electrode assembly was also prepared by the direct chemical deposition of platinum into the surface region of the membrane. Evaluation of the chemically deposited assembly showed it to be less active than those based on carbon supported catalysts. SEM &; TEM analysis indicate that this behaviour is due to the low surface area of the chemically deposited catalyst layer. The fuel cell performance with Nafion membranes is reported and is not as good as achieved with hydroxide ion conducting membranes suggesting that Nafion may not be suitable for DMAFC operation.     

Transport Properties of Ion‐Exchange Membranes During Pervaporation of Water‐Alcohol Mixtures

Abstract

Pervaporation properties of PESS ion‐exchange membranes in contact with water‐aliphatic alcohol mixtures were obtained. PESS ion‐exchange membranes were prepared by chemical modification of the interpenetrating polymer network system polyethylene‐poly(styrene‐co‐divinylbenzene). PESS membranes were loaded with different alkali metal ions as counterions. The obtained data showed that properties of PESS membranes depended strongly on the kind of counterions, degree of crosslinking, and difference in the polarities between water and organic component of the binary mixture. Results obtained for PESS membranes were compared with data obtained for Nafion 117 ion‐exchange membrane.     

SAXS characterization of the Nafion membrane nanostructure modified by radiation cross-linkage

The present study employs small-angle X-ray scattering (SAXS) to investigate the water-swollen structures of two types of Nafion membranes, commercial Nafion 117 membranes and the membranes synthesized from the Nafion precursor, subjected to gamma radiation. The membrane structure can be characterized by two-length scales, comprised the long-range order of lamellar crystalline domains in the matrix and the local order of ionic cluster domains. Both the long-range order lamella and local order cluster in the membranes are significantly affected by the radiation-induced cross-linking. We have extended a local order model to take into account the polydispersity effect, which can more satisfactorily reproduce the ionomer SAXS peak than other existing models. The structural parameters determined from the SAXS model analysis are self-consistent with those obtained from the model-independent Porod analysis. The modified membrane structure by the radiation cross-linking is very helpful for developing a high performance and low cost of direct methanol fuel cells.     

Effect of operating conditions on energy efficiency for a small passive direct methanol fuel cell

Energy conversion efficiency was studied in a direct methanol fuel cell (DMFC) with an air-breathing cathode using Nafion 117 as electrolyte membrane. The effect of operating conditions, such as methanol concentration, discharge voltage and temperature, on Faradic and energy conversion efficiencies was analyzed under constant voltage discharge with quantitative amount of fuel. Both of Faradic and energy conversion efficiencies decrease significantly with increasing methanol concentration and environmental temperature. The Faradic conversion efficiency can be as high as 94.8%, and the energy conversion efficiency can be as high as 23.9% if the environmental temperature is low enough (10 °C) under constant voltage discharge at 0.6 V with 3 M methanol for a DMFC bi-cell. Although higher temperature and higher methanol concentration can achieve higher discharge power, it will result in considerable losses of Faradic and energy conversion efficiencies for using Nafion electrolyte membrane. Development of alternative highly conductive membranes with significantly lower methanol crossover is necessary to avoid loss of Faradic conversion efficiency with temperature and with fuel concentration.     

Solution blown sulfonated poly(ether sulfone)/poly(ether sulfone) nanofiber‐Nafion composite membranes for proton exchange membrane fuel cells

A composite membrane of sulfonated poly(ether sulfone) (SPES)/poly(ether sulfone) (PES) nanofiber (NF) mat impregnated with Nafion was prepared and evaluated for its potential use as a proton conductor for proton exchange membrane (PEM) fuel cells. The supporting composite nanofibrous mat was prepared by solution blowing of a mixture of SPES/PES solution. The characteristics of the SPES/PES NF and the composite membrane, such as morphology, thermal stability, and performance of membrane as PEMs, were investigated. The performance of composite membranes was compared with that of Nafion117. The introduction of solution blown NFs to composite membranes modestly improved proton conductivity, water swelling, and methanol permeability. Therefore, composite membrane containing SPES/PES NFs can be considered as a novel PEM for fuel cell applications. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42572.     

Modification and evaluation of membranes for vanadium redox battery applications

Several commercial ion exchange membranes were evaluated for application in the vanadium redox battery. The polyether membrane, DF120 cationic exchange membrane, showed the highest permeability to vanadium ions and the worst chemical stability in V(V) solution, while the divinylbenzene membrane, JAM anionic exchange membrane, showed the lowest permeability to vanadium ions and the best chemical stability in V(V) solution. In order to impart some cationic exchange capacity to the JAM anionic exchange membrane, sodium 4-styrenesulfonate was used to modify the anionic membrane by in situ polymerization. Measurements by infrared spectroscopy (IR) and cationic ion exchange capacity (IEC) verified that the modification procedure imparts cationic exchange capability to the membrane. Incorporation of cationic exchange groups to the anionic exchange membrane further results in a reduction in permeability to vanadium ions. The current and energy efficiencies averaged over 8 charge/discharge cycles of the cell with the treated JAM membrane were higher than that with the untreated JAM membrane. The current and energy efficiencies of the cell with the treated JAM membrane did not change over several charge/discharge cycles, which indicates good chemical stability of the treated membrane in the vanadium redox cell. The average efficiencies of the cell with the treated JAM membrane are higher than that with Nafion 117 over 8 charge/discharge cycles.