In situ crosslinking of polyoxometalate-polymer nanocomposites for robust high-temperature proton exchange membranes

The most practical high-temperature proton exchange membranes (PEMs) are phosphoric acid (PA)-doped polymer electrolytes. However, due to the plasticizing effect of PA, it is a challenge to address the trade-off between the proton conductivity and the mechanical performance of these materials. Here, we report an effective strategy to fabricate robust high-temperature PEMs based on the in situ electrostatic crosslinking of polyoxometalates and polymers. A comb copolymer poly(ether-ether-ketone)-grafted-poly(2-ethyl-2-oxazoline) (PGE) with transformable side chains was synthesized and complexed with H₃PW₁₂O₄₀ (PW) by electrostatic self-assembly, forming PGE/PW nanocomposite membranes with bicontinuous nanostructures. After a subsequent PA-treatment of these membranes, high-temperature PEMs of PGE/PW/PA ternary nanocomposites were obtained, in which the in situ electrostatic crosslinking effect between PW and PGE side chains was generated in the hydrophilic domains of the bicontinuous structures. The microphase separation structure and the electrostatic crosslinking feature endow the PGE/PW/PA membranes with excellent anhydrous proton conductive ability while retaining high mechanical performance. The membranes show a high proton conductivity of 42.5 mS/cm at 150 °C and a high tensile strength of 13 MPa. Our strategy can pave a new route based on electrostatic control to design nanostructured polymer electrolytes.     

Compensation of the siphoning effect in nonaqueous capillary electrophoresis by vial lifting

Increasing the sample load in nonaqueous capillary electrophoresis through the use of wide-bore capillaries is a good way to scale up analytical separations to semipreparative level. However, obtaining high efficiency requires the use of special instrumentation to eliminate siphoning. When wide-bore capillaries are employed, relatively large solvent volumes are transported from inlet to outlet vial, and due to the difference in liquid levels a siphoning flow from outlet to inlet is established. Siphoning induces a deviation from the plug-like flow profile and adversely affects the separation efficiency. In this study the use of wide-bore capillaries in nonaqueous capillary electrophoresis was examined with compensation for siphoning by lifting of the inlet vial. The inlet vial is raised at a speed appropriate for maintaining equal levels of liquid in the inlet and outlet vials. The optimal lift rate was determined empirically from a series of runs in which the lift rate was varied. As well, a simple theoretical model was devised for the calculation of lift rates. The model was successfully applied for the 200 microm and 320 microm ID capillaries but for the 530 microm ID capillary the predicted optimal lift rate was too low. Evidently this was because the theory was unable to account for the effect of siphoning on the migration times. Three model compounds, bumetanide, furosemide and ethacrynic acid, were separated using an acetonitrile-ethanol mixture (50:50, v/v) with potassium acetate (1 mM) or ammonium acetate (5 mM) as electrolyte. Good separation of bumetadine and ethacrynic acid was obtained even with a 530 microm ID capillary when the lift rate was carefully optimized. Without elimination of siphoning the peaks would not have been detectable. The viscosities and electrical conductivities of the electrolyte solution measured at different temperatures showed that viscosity as well as conductivity decreased with increasing temperature. The temperature dependence of the conductivity was used to estimate the temperature inside the CE capillary.     

燃料电池用聚合物质子交换膜的研究进展

质子交换膜（PEM）是质子交换膜燃料电池的核心组件之一,具有隔绝阴阳极、提供质子传递通道和阻止燃料渗透的作用. 商业化应用的全氟磺酸PEM存在燃料渗透严重、高温条件下导电性差和成本高的问题,开发性能优良的聚合物PEM显得很有必要. 本文讨论了近年来聚合物PEM的研究进展,分别从聚合物的主链、支链和交联结构角度介绍了分子结构对薄膜相分离、质子导电性、稳定性和电池性能等性能的影响,并讨论了聚合物分子结构设计方面存在的问题,最后对燃料电池用聚合物PEM在未来的发展方向进行了展望.     

后磺化法精确可控合成主链型磺化聚苯喹喔啉及其质子交换膜性能研究

以不同摩尔比的4,4′-双(4-(2-苯基乙二酮基)苯氧基联苯、4,4′-双(2-苯基乙二酮基)二苯醚与3,3′,4,4′-四氨基联苯共聚制备聚喹喔啉,经后磺化法得到一系列磺化度可控的磺化聚苯基喹喔啉(SPPQ).模型化合物确认,磺酸基团精确接入电子云密度较高的含醚键的联苯片段的2,2′-位上,证明通过单体分子结构设计与后磺化法结合,可使磺酸基团在温和条件下,按预想接入到聚合物主链上,达到磺化度和磺化位置精确可控的目的. SPPQ的相对黏度均在3.8 dL/g以上.通过溶液涂膜法制备的主链型磺化聚苯基喹喔啉质子交换膜(SPPQ PEM)的吸水率都低于39%,尺寸变化率为2.1%~13%,且随着IEC和温度的提高而线性增加.如,80℃下,IEC高达2.21 meq/g的SPPQ-5的膜面和膜厚方向的尺寸变化率仅为11%和13%,具有良好的形状维持能力.热重分析表明,SPPQ PEM在320℃左右脱去磺酸基团,550℃左右发生聚合物主链降解,具有良好的热稳定性. Fenton试剂测试表明,SPPQ PEM开始破碎的时间随IEC的增加而缩短,在20℃时,IEC较低的SPPQ-1 (1.29 meq/g)破碎时间可达151 h,而IEC较高的SPPQ-5(2.21 meq/g)破碎时间缩短至81 h. PEM的质子传导率随温度和IEC的增加而显著提高,最高可达64 mS/cm,由于磺酸基团和喹喔啉酸碱对的形成以及吸水率偏低的原因,这一数值远低于Nafion.     

A review on the role of proton exchange membrane on the performance of microbial fuel cell

Proton exchange membranes (PEMs) are the most frequently used separators in microbial fuel cells (MFCs). The role of proton transportation in MFC performance makes PEMs one of the most important components in the cell. The effect of PEMs in MFC performance is commonly determined according to generated power density and coulombic efficiency. Nafion is the commonly used membrane in MFCs, but there are still a number of problems associated with the use of Nafion including oxygen transfer rate, cation transport and accumulation rather than protons, membrane fouling and substrate loss. Moreover, additional problems can also be attributed to the effect of PEMs including internal resistance and pH change in MFCs. Recent developments in PEM performance are attributed to two categories including utilization of other types of membranes and improvements in Nafion by pre‐treatment methods. Copyright © 2014 John Wiley & Sons, Ltd.     

Highly durable proton exchange membranes for low temperature fuel cells

A novel method has been proposed to fabricate Nafion/poly(tetrafluoroethylene) (PTFE) composite proton exchange membranes (PEMs) with high durability and high chemical stability. In this method, Nafion ionomers were first converted into the Na(+) form, they were then fixed on PTFE frame micropores, and then the polymer was heat-treated at 270 degrees C. The chemical stability tests of the novel composite PEMs by Fenton's reagent demonstrate the significant improvement in the chemical durability. The Nafion/PTFE composite PEMs also show an excellent physical stability, and its RH-generated stress is 0.6 MPa at 25 RH% and 90 degrees C, substantially smaller than 3.1 MPa for pure Nafion membrane under the same conditions. In an in situ accelerating RH cyclic experiment, the degradation in the open circuit voltage (OCV) of the fuel cell assembled with the novel composite PEMs is 3.3 mV/h, significantly lower than 13.2 mV/h for a fuel cell assembled with the commercial Nafion membrane.     

Wound Healing Attributes of Polyelectrolyte Multilayers Prepared with Multi‐l‐arginyl‐poly‐l‐aspartate Pairing with Hyaluronic Acid and γ‐Polyglutamic Acid

Biodegradable multi‐l ‐arginyl‐poly‐l ‐aspartate (MAPA), more commonly cyanophycin, prepared with recombinant Escherichia coli contains a polyaspartate backbone with lysine and arginine as side chains. Two assemblies of polyelectrolyte multilayers (PEMs) are fabricated at three different concentration ratios of insoluble MAPA (iMAPA) with hyaluronic acid (iMAPA/HA) and with γ‐polyglutamic acid (iMAPA/γ‐PGA), respectively, utilizing a layer‐by‐layer approach. Both films with iMAPA and its counterpart, HA or γ‐PGA, as the terminal layer are prepared to assess the effect on film roughness, cell growth, and cell migration. iMAPA incorporation is higher for a higher concentration of the anionic polymer due to better charge interaction. The iMAPA/HA films when compared to iMAPA/γ‐PGA multilayers show least roughness. The growth rates of L929 fibroblast cells on the PEMs are similar to those on glass substrate, with no supplementary effect of the terminal layer. However, the migration rates of L929 cells increase for all PEMs. γ‐PGA incorporated films impart 50% enhancement to the cell migration after 12 h of culture as compared to the untreated glass, and the smooth films containing HA display a maximum 82% improvement. The results present the use of iMAPA to construct a new layer‐by‐layer system of polyelectrolyte biopolymers with a potential application in wound dressing.     

燃料电池用侧链型磺化聚砜质子交换膜的性能

在制备氯甲基化聚砜(CPS)的基础上,以1,2-二羟基苯-3,5-二磺酸钠为试剂,通过亲核取代反应制备一种侧链末端为磺酸基团的侧链型磺化聚砜(PS-BDS),并采用溶液浇注法制备相应的质子交换膜(PEM),研究温度对PEM性能的影响规律。 结果表明,由于亲水基团远离疏水聚合物主链,该PEM能够形成亲水微区远离疏水微区的相分离结构,亲水区域对主链的影响较小,该PEM在高磺化度下仍能保持较好的尺寸稳定性,随着温度的升高,PEM的吸水率(WU)、吸水溶胀率(SW)和质子传导率(PC)升高,其中PS-BDS-4(离子交换容量为1.57 mmol/g)在25和85 ℃时的SW仅为22.1%和55.0%,甲醇的渗透率(DK)仅为10.17×10^-7 cm²/s,低于商业化的Nafion115(16.8×10^-7 cm²/s)和Nafion117(23.8×10^-7 cm²/s),表现出很好的综合性能。     

Electro-combustion of polyacrylates with boron-doped diamond anodes

The electro-combustion of water soluble polymeric contaminants like polyacrylates (PA) in aqueous acid solution using a boron-doped diamond (BDD) anode has been investigated by bulk electrolysis in 1 mol dm⁻³ HClO₄ under galvanostatic conditions in a wide range of PA concentrations and current densities. In all cases complete electro-combustion of PA has been achieved and this is the first successful report for the electro-combustion of soluble organic polymers.The experimental chemical oxygen demand (COD) and instantaneous current efficiency (ICE) values are well predicted from a theoretical model which suppose that the rate of electro-combustion of PA with electrogenerated active intermediates (probably hydroxyl radicals) is a fast reaction and is controlled by mass transport of PA towards the anode (concept of the “ideal anode” for electro-combustion).     

Non-Fluorinated Polymer Composite Proton Exchange Membranes for Fuel Cell Applications – A Review

The critical component of a proton exchange membrane fuel cell (PEMFC) system is the proton exchange membrane (PEM). Perfluorosulfonic acid membranes such as Nafion are currently used for PEMFCs in industry, despite suffering from reduced proton conductivity due to dehydration at higher temperatures. However, operating at temperatures below 100 °C leads to cathode flooding, catalyst poisoning by CO, and complex system design with higher cost. Research has concentrated on the membrane material and on preparation methods to achieve high proton conductivity, thermal, mechanical and chemical stability, low fuel crossover and lower cost at high temperatures. Non-fluorinated polymers are a promising alternative. However, improving the efficiency at higher temperatures has necessitated modifications and the inclusion of inorganic materials in a polymer matrix to form a composite membrane can be an approach to reach the target performance, while still reducing costs. This review focuses on recent research in composite PEMs based on non-fluorinated polymers. Various inorganic fillers incorporated in the PEM structure are reviewed in terms of their properties and the effect on PEM fuel cell performance. The most reliable polymers and fillers with potential for high temperature proton exchange membranes (HTPEMs) are also discussed.     

Water induced phase segregation in hydrocarbon proton exchange membranes

Proton exchange membranes(PEMs) are a key material for proton exchange membrane fuel cells(PEMFCs). Non-fluorinated hydrocarbon PEMs are low-cost alternatives to Nafion, but limited by the low proton conductivity, because of the weak phase segregation structure and narrow ion-transport channels.Various efforts have been taken to improve the performance of hydrocarbon PEMs, but mostly with complex methodologies. Here we demonstrate a simple, yet very efficient method to create phase segregation structure inside a typical hydrocarbon PEM, sulfonated poly(ether ether ketone)(SPEEK). By simply adding appropriate amounts of water into the DMF solvent, the resulting SPEEK membrane exhibits widened ion-transport channels, with the phase size of 2.7 nm, as indicated by both molecular dynamic(MD) simulations and transmission electron microscope(TEM) observations, and the proton conductivity is thus improved by 200%. These findings not only further our fundamental understanding of hydrocarbon PEMs, but are also valuable to the development of low-cost and practical fuel cell technologies.     

Cell surface engineering with polyelectrolyte multilayer thin films

Layer-by-layer assembly of polyelectrolyte multilayer (PEM) films represents a bottom-up approach for re-engineering the molecular landscape of cell surfaces with spatially continuous and molecularly uniform ultrathin films. However, fabricating PEMs on viable cells has proven challenging owing to the high cytotoxicity of polycations. Here, we report the rational engineering of a new class of PEMs with modular biological functionality and tunable physicochemical properties which have been engineered to abrogate cytotoxicity. Specifically, we have discovered a subset of cationic copolymers that undergoes a conformational change, which mitigates membrane disruption and facilitates the deposition of PEMs on cell surfaces that are tailorable in composition, reactivity, thickness, and mechanical properties. Furthermore, we demonstrate the first successful in vivo application of PEM-engineered cells, which maintained viability and function upon transplantation and were used as carriers for in vivo delivery of PEMs containing biomolecular payloads. This new class of polymeric film and the design strategies developed herein establish an enabling technology for cell transplantation and other therapies based on engineered cells.     

Multi-gas sensing based on photoacoustic spectroscopy using tunable laser diodes

Multi-hydrogenated compounds detection based on photoacoustic (PA) spectroscopy is reported. Three near-infrared semiconductor lasers are used with a resonant PA cell operated in its first longitudinal mode to monitor methane, water vapour and hydrogen chloride in the parts per million range. The design of our cell results from simulations performed in order to optimise its performances. Influence of the buffer gas on the PA signal has also been analysed, both theoretically and experimentally. A reduction of the PA signal of almost one order of magnitude has been observed between N(2) and He, which demonstrates the importance of the buffer gas in PA spectroscopy. Finally, detection limits of 0.5 ppm of CH(4) and 3 ppm of HCl has been achieved experimentally in nitrogen and an H(2)O sensitivity of 0.2 ppm has been estimated.     

Suitable combination of promoter and micellar catalyst for chromic acid oxidation of formaldehyde to formic acid in aqueous acid media at room temperature

The chromic acid oxidation of formaldehyde in micellar solution of sodium dodecyl sulphate (SDS)/TX-100 at room temperature has been investigated under pseudo first-order condition. Heterocyclic bases such as picolinic acid (PA), 2,2′-bipyridine (bipy), 1,10-phenanthroline (phen) have been employed which acts as a promoter. The rate of this oxidation reaction increased 50 times by combination of bipy and SDS micelle compared to rate in pure aqueous media. Here, we can avoid hazardous organic solvents, high pressure and temperature which are required for conventional preparation of formic acid. The catalytic effect of SDS/TX-100 micelle has been explained.     

基于一锅法的磺化聚砜质子交换膜的性能

以双酚A型聚砜(PSF)为基质材料,通过傅-克烷基化反应在PSF主链引入—NCO活性基团,制备乙基异氰酸化聚砜(PS-SA)。 在制备PS-SA的基础上,采用两步一锅法,PS-SA与2-萘酚-6,8-二磺酸钾通过亲核取代反应,制备一种侧链含有萘环的萘磺酸型磺化聚砜PS-NS,充分表征聚合物的化学结构,以溶液浇注的方法制备质子交换膜,研究了温度对PS-NS膜的吸水率(WU,Water Uptaking)、吸水溶胀性(Swelling Ratio)、质子传导率(Proton Conductivity)等基本性能的影响。 结果表明,PS-NS膜由于亲水基团距离较远,能够很容易形成相分离结构,所制备的质子交换膜高WU下尺寸稳定性仍然很高,其中PS-NS-4膜(磺酸基团键合量为1.42 mmol/g)在25和85 ℃的WU高达27.2%和40.3%,但是相应的吸水溶胀性仅为25.2%和57.2%,与相同条件下Nafion115膜的性能十分接近。     

Electric conductivity of concentrated aqueous solutions of propionic acid, sodium propionate and their mixtures

Specific electric conductivity (EC) of concentrated aqueous solutions of propionic acid (PA), sodium propionate (SP), and water/PA/SP mixtures is measured in the temperature range of 15–90°C. Specific EC passes a maximum at the increase in the electrolyte concentration in the mixtures of water/PA, water/SP, and water/PA/SP containing a similar PA concentration. The maximum EC value of the aqueous PA solution at the given temperature is used as the generalizing term. It is shown that the values of reduced EC (ratio of EC and its maximum value at the given temperature) fall on a single curve in the whole studied range of temperatures and concentrations of the water/PA mixture. The EC activation energy is calculated for all the studied solutions. It is found that the EC activation energy of these solutions decreases at the temperature increase and grows at the increase of the concentration of electrolyte.     

An improved method for the durability of the flame retardant PA66 fabric

This paper describes an attempt in order to improve the durability of the flame retardant polyamide 66 (PA66) fabric prepared by the reaction of surface photografting with acrylamide (AM) under UV irradiation. In this study, N,N′-methylene bisacrylamide (MBAAm) combined with acrylamide has been used as a photosensitive monomer during flame retardant finishing of the PA66 fabric sample. “Durable efficiency” has been introduced to evaluate the durability of AM/MBAAm-g-PA66 fabric after 50 times washing with the 0.5 % commercial grade detergent solution. The result indicates that durable efficiency reaches its maximal value of 94.5 % when the MBAAm concentration is 5.0 mass%. The effect of MBAAm on the flame retardancy, thermal stability and tensile properties of the treated PA66 fabric has been investigated, respectively. And an interesting phenomenon shows that although MBAAm could improve the thermal stability of the treated fabric significantly at high temperature, it could have a negative effect on the flame retardancy and tensile properties of the fabric sample when its concentration is high. Its possible mechanism has been discussed here.     

支化型聚苯并咪唑高温质子交换膜的制备与性能研究

通过引入1,3,5-苯三酸作为支化结构,制备了一种新型的支化型聚醚聚苯并咪唑(OPBI)高温燃料电池质子交换膜,并对支化OPBI质子交换膜的磷酸掺杂率、抗氧化稳定性、机械性能以及质子传导率等一系列性质进行了深入研究.与线型聚苯并咪唑(PBI)相比,支化OPBI具有独特的三维空间结构,极大地提高了磷酸掺杂量,随着支化度的提高,磷酸掺杂率和质子传导率随之提高.支化度为9%时,聚合物的磷酸掺杂率高达9.2 PRU?1,质子传导率达到0.0314 S/cm.此外,支化OPBI膜的溶解性较线型PBI也有较大的改善,进一步提高了聚合物的可加工性.同时,支化OPBI膜的热稳定性和抗氧化稳定性也得到了一定程度的提高,虽然机械性能略有下降,但仍能满足高温燃料电池的使用要求.     

Facilitating the culture of mammalian nerve cells with polyelectrolyte multilayers

When neuron-like cells (NLCs) derived from pluripotent embryonal carcinoma cells (P19) are cultured on bare tissue culture substrates, they require a monolayer of fibroblast cells to exhibit normal neurite outgrowth, behavior typical of neuronal cultures. However, substrate treatment with polyelectrolyte multilayers (PEMs) composed of poly(allylamine hydrochloride) (PAH) and poly(styrenesulfonic acid) (PSS) significantly improved these cultures. Cell morphology was more spread, indicative of healthy cells, and direct attachment of neuronal cell bodies to the treated surface was observed. Neuronal outgrowth across the surface was not dependent on an underlying fibroblast monolayer with the PEMs surface treatment. Additionally, the PEMs surface treatment can be used to condition various surfaces, facilitating neuronal cultures on surfaces which are natively hydrophilic (tissue culture polystyrene) or hydrophobic (poly(dimethylsiloxane), PDMS). Microfluidic networks were used to micropattern the PEMs onto PDMS, resulting in confined regions of cellular attachment and directed neuronal outgrowth. The ability of PEMs to encourage NLC attachment without supporting cells to a variety of surfaces and surface geometries greatly simplifies neuronal culture methodology and enables neuronal investigations in new environments.     

Polymer electrolyte membranes for the direct methanol fuel cell: A review

The direct methanol fuel cell (DMFC) has the potential to replace lithium‐ion rechargeable batteries in portable electronic devices, but currently experiences significant power density and efficiency losses due to high methanol crossover through polymer electrolyte membranes (PEMs). Numerous publications document the synthesis and characterization of new PEMs for the DMFC. This article reviews this research, transport phenomena in PEMs, and experimental techniques used to evaluate new PEMs for the DMFC. Although many PEMs do not show significant improvements over Nafion®, the benchmark PEM in DMFCs, experimental results show that several new PEMs exhibit lower methanol crossover at similar proton conductivities and/or higher DMFC power densities. These results and recommendations for future research are discussed. © 2006 Wiley Periodicals, Inc. J Polym Sci Parts B: Polym Phys 44: 2201–2225, 2006