采用Nafion粘结剂的PEMFC氧电极研究

研究了聚合物电解质燃料电池（PEMFC）中以Nation溶液取代PTFE乳液作粘结剂的效果．并对催化剂层内Nafion含量进行了优化，同时探讨了气体工作压力和离子交换膜的影响，实验发现：1．使用Nafion溶液后显著提高电池性能，Nafion含量为2mg·cm－2时性能技好；2．气体压力增大改善了电池位能；3．使用Nafion115膜的电池性能优于使用Nafion117膜的电池．要进一步提高电池性能，减小欧姆控制区的斜率是必要的．     

聚合物电解质膜燃料电池薄电极制备技术的研究

为降低聚合物电解质膜燃料电池 (PEMFC)电极中铂的载量 ,本文建立一种新的薄电极制备技术 (TEFT) ,制备了表面平滑、颗粒分布均匀的低铂载量电极 .结果表明当电极的铂载量为 1mg/cm2 ,用Nafion 117膜作电解质时 ,电池的最大功率密度达 0 30W·cm-2 .系统地考察了阴极中不同PTFE和Nafion含量对PEMFC性能的影响 .     

A New Nitric Oxide Gas Sensor Based on Reticulated Vitreous Carbon/Nafion and Its Applications

Reticulated vitreous carbon (RVC), and Nafion membrane are used to fabricate a composition electrode to measure nitric oxide (NO) concentration amperometrically in the gas phase. Limit of detection was found to be 6 ppb at an applied voltage of 0.66 V (vs. mercury sulfate reference electrode) with average response time of less than 30 seconds. The response of the sensor was linearly dependent on the concentration over the whole tested range from 19 ppb‐50 ppm of NO. Simplicity in electrode fabrication and consistent performance between individual sensors make RVC and Nafion attractive materials for detecting very low levels of nitric oxide gas in routine analysis.     

Electrodes supported on ion-exchange membranes as sensors in gases and low-conductivity solvents

An electroanalytical sensor is proposed that is suitable for the detection of electroactive analytes present in gases or low-conductivity solvents where supporting electrolytes cannot be introduced. It consists of a porous working electrode supported on one surface of a cationic ion-exchange membrane (Nafion 417), the other surface of which is in contact with an electrolyte solution containing the counter and reference electrodes. Such an ion-exchange membrane replaces a conventional supporting electrolyte dissolved in the analyte sample and can be regarded as a solid polymer electrolyte (SPE) confined in the close neighbourhood of the working electrode. Alternative procedures followed for coating SPE membranes with various materials (Pt, Au, C or Hg) are described, together with the general properties displayed by the resulting composite electrodes in analyte-free gaseous or liquid media. These assemblies have been used as both voltammetric and amperometric sensors for electroactive analytes present in gases and in aqueous or organic solvents with no supporting electrolyte. The results indicate that their performance is similar to that expected on conventional electrodes, the only difference being a slightly lower degree of reversibility for the electrode processes investigated. Detection limits for some analytes were calculated and the use of SPE electrodes as sensors suitable for the continuous monitoring of electroactive analytes dispersed in gases or non-conductive liquids is reported. Preliminary attempts to use these assemblies for the determination of trace metals in low-conductivity solvents by anodic stripping voltammetry are discussed.     

粘结剂聚四氟乙烯乳液经过乙醇预处理后对气体扩散电极性能的影响

在气体扩散电极的制作工艺中,加入乙醇对粘结剂聚四氟乙烯(PTFE)进行预处理.通过伞自动微孔物理化学吸附仪对气体扩散电极进行BET比表面积、Langmuir比表面积、孔分布等进行测试,并用扫描电子显微镜(SEM)检测观察电极表观形貌.以锌电极作为负极组装成锌空气电池,检测在不同的电流密度下气体扩散电极相对锌电极的电位变化,研究PTFE乳液经过乙醇预处理后对电极性能的影响.结果显示,PTFE乳液经过乙醇处理后,先膨胀后收缩,能够增加催化层和气体扩散层的孔隙结构和比表面积,从而使得电极有效电化学反应场所相应增多,减低电极在大电流密度条件下放电时的极化过电位.     

Effects of Humidity,Temperature and Bismuth Electrodeposition on Electroanalytical Performances of Nafion‐coated Printed Electrodes for Cd2+ and Pb2+ Detection

The synergistic use of Nafion polymeric membrane and in situ electrodeposited bismuth film is a worthwhile strategy to develop electrochemical sensors for the detection of Cd²⁺ and Pb²⁺. However, Nafion thin films morphological and conductivity properties have a strong dependence on the environmental conditions, such as relative humidity and temperature, while the bismuth in situ electroplating can affect the repeatability of measurements. With the aim to overcome these drawbacks, the effects of the storage environmental conditions were investigated to improve the morphological stability and electroanalytical performances of Nafion film‐based sensor for the detection of Cd²⁺ and Pb²⁺. Nafion‐coated graphite‐based screen‐printed electrodes were stored at different humidity and temperature conditions and characterised by using square wave anodic stripping voltammetry, cyclic voltammetry, electrochemical impedance spectroscopy, and scanning electron microscopy. Significant differences were observed at the varying of humidity conditions, with an enhancement of sensor electrochemical performances at lower humidity. Furthermore, different approaches for bismuth in situ electrodeposition on Nafion‐coated screen‐printed electrodes were compared by using overlap or removal approach. This study disclosed considerable differences in the electrochemical performances and morphology of the resulting bismuth‐sensor, obtaining an enhancement of the working stability for the removal approach.     

Electrochemical and electrocatalytic behaviors of Safranin O/Nafion film deposited on the glassy carbon electrode

The glassy carbon (GC) electrode modified with Nafion and Safranin O (SFO) was prepared and its electrochemical properties were investigated. The SFO molecules were strongly and irreversibly adsorbed on the Nafion — modified GC surface. The electrochemical behavior and mechanism for interactions of the SFO molecules with the Nafion film were investigated through cyclic voltammetric method. The electrocatalytic reduction of nitric oxide was performed at this modified electrode by cyclic voltammetric and hydrodynamic amperometric techniques. The Nafion membrane played a duel role as a matrix for the SFO immobilization and also helped to partition the nitric oxide from the solution phase. The diffusion coefficient of NO at the SFO/Nafion/GC modified electrode was calculated using chronoamperometry. The dependence of response currents on the concentration of NO was examined and was linear in the range of 0.05–1.9 mM of NO.     

Nafion/PTFE and zirconium phosphate modified Nafion/PTFE composite membranes for direct methanol fuel cells

We prepared Nafion/PTFE (NF) and zirconium phosphate (ZrP) hybridized Nafion/PTFE composite membranes (NF–ZrP). NF–ZrP composite membranes were prepared via two processes. One is impregnating sub-μm porous PTFE membrane directly in a Nafion/ZrOCl₂ solution (NF–Zr–d). The other is impregnating sub-μm porous PTFE membrane in a Nafion solution to prepare NF composite membrane, and then the NF membrane was impregnated in a ZrOCl₂ aqueous solution via in situ precipitation method (NF–Zr–I). The ZrOCl₂ inserted in NF composite membranes was then reacted with phosphoric acid to form ZrP and thus NF–ZrP–d and NF–ZrP–I composite membranes were obtained. The direct methanol fuel cell (DMFC) performances of membrane electrode assemblies prepared from Nafion-117, NF, NF–ZrP–d, and NF–ZrP–I composite membranes were investigated. The effects of introducing sub-μm porous PTFE film and ZrP particles into Nafion membranes on the DMFC performance were investigated. The influence of ZrP hybridizing process into NF membranes (the process of preparing NF–ZrP–I is inserting ZrOCl₂ into NF membranes after Nafion is annealed and the process of preparing NF–ZrP–d is mixing ZrOCl₂ into a Nafion solution before Nafion is annealed) on the morphology of NF–ZrP composite membranes and thus on the DMFC performance was also discussed.     

A regenerable pseudo-reagentless glucose biosensor based on Nafion polymer and l,1''-dimethylferricinium mediator

Glucose oxidase was immobilized onto electrodes by co-deposition from an aqueous solution containing the diluted ion-exchange polymer Nafion. The cationic exchange property of the polymer was used to provide high local concentrations of l,1'-dimethylferricinium (DMFc⁺) mediator in the film by exchange from solution. The mediated electrodes were operated at +200 mV (vs. ), and the Nafion film was shown to reduce interfering current from ascorbate anion. Cyclic voltammetric analysis revealed a fourteen-fold increase in the effective DMFc⁺ activity at the electrode after extraction into the film. The sensitivity to glucose was 52 μA/cm²/mM in a solution containing 0.09 mM DMFc⁺, which is at least three-fold greater than reported for similar electrodes using hydrogen peroxide detection at +650 mV, with a response time of less than 1 min for a 10 μm thick membrane. Oxygen interference was significant, requiring deaeration of the solution before analysis. The electrodes exhibited no significant decrease in sensitivity for more than 50 days on storage in acetate buffer. Electrodes covered with 8000 MWCO dialysis membrane slowed the exchange of DMFc⁺ with the solution such that the Nafion film functioned as a mediator reservoir. This permitted reagentless analysis of glucose, typically capable of twenty assays when measuring concentrations between 0.1 and 1 mM. The sensitivity for glucose was 7.85 μA/cm²/mM, which is 15% of the sensitivity for the electrode without the dialysis membrane. The detection limit was 20 μM, with a linear range extending to about 3 mM, giving a dynamic range of over two orders of magnitude. Thus where some sacrifice of sensitivity and response rate may be made, the dialysis membrane cover enables multiple analyses in a reagentless biosensor scheme.     

A thin-layer electrochemical detector coated with nafion film for liquid chromatography

The selectivity and analytical application of a thin-layer electrochemical detector comprised of glassy carbon electrode coated with Nafion film were investigated. As a result of the ion-exchange characteristics of the Nafion polymer, the selectivity and stability were improved greatly. The coated electrode has a good response only for cations with the same sensitivity as an uncoated (bare) electrode, but not for anions, and the response for neutral molecules is decreased three-fold. The diffusion of electroactive compounds in Nafion film is discussed based on the results of flow injection experiments. The peak current at the coated electrode was independent of the flow-rate of the mobile phase. Electrode poisoning due to protein adsorption was minimized. The use of 30% methanol or 10% acetonitrile in the mobile phase did not affect the performance of the coated electrode. Various analytes having three kinds of charge state, i.e., anionic, cationic and neutral, were tested. Liquid chromatography with electrochemical detection of ascorbic acid, norepinephrine, epinephrine, dopamine and uric acid was demonstrated.     

The Electrochemical Behavior and the Quantitative Determination of Nitrogen Dioxide at a Solid Polymer Electrolyte Supported Pt‐Au Electrode

The electrochemical behavior of NO₂ at Au/Nafion, Pt/Nafion and Pt‐Au/Nafion electrodes was investigated by using electrochemical and SEM methods, respectively. It was found that the Pt‐Au/Nafion electrode showed higher electrocatalytic activity than Pt/Nafion and Au/Nafion electrodes. The net current density of Au/Nafion electrode decayed significantly during the reaction, though it showed high initial value. Pt/Nafion and Pt‐Au/Nafion electrodes, on the contrary, showed good stability. A quantitative determination of NO₂ concentration was carried out at Pt‐Au/Nafion electrode and a satisfactory linear relationship was found for the NO₂ concentration in the range of 0–100 ppm.     

全氟磺酸锂电导率式湿度传感器

以碳纸为电极,Nafion溶液再铸薄膜为感湿材料,并用氯化锂将膜转换成Li+型,制备了固体聚合物电解质湿度传感器.测定了不同相对湿度下,传感器的电导率响应与相对湿度之间关系.结果表明:在相对湿度为10%～97%范围内,传感器的电导率响应对数与相对湿度之间成良好的线性关系,线性度为0.997;传感器响应的时间为40s左右;于200h内稳定性和重复性良好.     

Crystallinity enhancement of Nafion electrolyte membranes assisted by a molecular gelator

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

Photoelectrocatalytic decomposition of gaseous isopropanol in a polymer electrolyte photoreactor

A photoelectrochemical reactor constructed as a proton exchange membrane fuel cell was utilized to electrochemically enhance the photocatalytic decomposition of gas-phase isopropanol. Nafion membrane was employed to serve as solid electrolyte to establish an electrochemical circuit for the gaseous photocatalytic reaction. The electrical current density of photoanode was found to correspond to the variation of the applied bias and relative humidity of the inlet gas. Photocatalytic decomposition rate was remarkably increased by 20 % by applying a bias potential of 5 V. The effect of relative humidity exhibited multiple effects for membrane conductivity of Nafion and efficiency of photocatalytic decomposition reaction.     

Influence of Analyte Flow Rate on Signal and Response Time of the Amperometric Gas Sensor with Nafion Membrane

This paper presents results of an investigation on influence of volumetric flow rate on the signal and response time of a prototype of sulfur dioxide gas sensor with Nafion membrane. The sensors differing in type of working electrode and composition of internal electrolyte were compared. We used Au and Pt working electrodes obtained via vacuum sublimation deposition on a Nafion membrane surface. The electrolytes were aqueous solutions of sulfuric acid of the summary concentration 5 mol dm^?3 (electrolyte A). The electrolyte B contained an addition of dimethylsulfoxide (DMSO); the water/DMSO molar ratio was 2 : 1. Based on a proposed equation, which takes diffusion resistance into account, the obtained sensor signals were analyzed for the flow rate within a range of 0–100 cm³ min^?1. The sensor response time was also determined for the above flow rate range.     

Nafion膜电极对氧的催化还原的研究(I)──CoTSPc和CoTMAP的循环伏安对比

制备了两组Nafion膜电极(膜中分别分布有带正、负电荷的过渡金属大环配离子),并用循环伏安法研究比较了这两组电极对氧催化还原性能,探讨了配离子和Nafion膜之间的静电作用对电极催化性能影响的规律,同时对其它因素的影响及电荷在Nafion膜中传递的机理也进行了讨论。     

质子交换膜燃料电池电极的一种新的制备方法

提出一种新的电极制备方法 ,在薄层催化层电极制备中加入造孔剂 ,并使用喷涂方法 ,使质子交换膜燃料电池 (PEMFC)电极中铂担量降到 0 .0 2mgPt/cm2 .与文献方法相比 ,新方法过程简单、成本低、易放大 .并通过实验得到电极的最佳组成为 :催化剂 :造孔剂 :Nafion =3:3:1 .采用此方法制备的电极 (0 .0 2mgPt/cm2 )与Nafion 1 1 5膜组装成电池 ,单池工作电压为 0 .7V时 ,每毫克铂可产生 2 0A的电流 ,每千瓦电池组仅需 72mgPt .     

Silica‐modified Electrodes for Electrochemical Detection of Malachite Green

New silica‐modified glassy carbon electrodes prepared with three different sorts of ordered mesoporous silica (OMS) were characterized and tested for the electrochemical detection of Malachite Green (MG). The electrodes were prepared by drop casting using silica suspensions and, for stability sake, a Nafion coating was deposited on the electrode top by the same technique. Square wave anodic stripping voltammetry was used to investigate the effect of various experimental parameters (deposition time, solution pH, silica type and concentration) on the performance of the modified electrodes. The best electrode (GC/MCM‐41‐NH₂/Nafion) with detection limit 0.36 μM, sensitivity 0.164±0.003 A/M; linear domain 1–6 μM was applied to detect MG in a commercial product commonly used as biocide in aquaria for ornamental fish.     

Determination of Ammonia/Air Diffusion Coefficient Using Nafion Lined Tube

Abstract

Trace gaseous ammonia in air was removed in a laminar flow Teflon tube lined with Nafion film. The ammonia deposition pattern was obtained by sectioning the Nafion lining, extracting with an aqueous solution, and measuring the concentration with an ammonia gas electrode. Mass transport analysis of the deposition pattern demonstrated that the ammonia was removed from the air stream at a rate controlled by gaseous diffusion. The ammonia/air diffusion coefficient equalled 0.228 ± 0.012 cm² s^?1 at 1 atm 25°C. No dependence on relative humidity was observed over the range 10–92%.     

Preparation of Nafion/PTFE/Zr(HPO4)2 composite membranes by direct impregnation method

The viscosities of as received 5.1 wt.% Nafion solutions (EW = 1100, Du Pont Co) blended with various concentrations of ZrOCl₂ were studied. We show the solution viscosity decreases as the wt. ratio of [ZrOCl₂]/[Nafion] is increased from 0.0 to 0.03, then the viscosity does not change significantly as the wt. ratio of [ZrOCl₂]/[Nafion] is increased from 0.03 to 0.16, and then the viscosity increases dramatically as the wt. ratio of [ZrOCl₂]/[Nafion] is increased above 0.16. Four Nafion solutions consisting of 5.1 wt.% Nafion and ZrOCl₂ with [ZrOCl₂]/[Nafion] wt. ratios of 0.019–0.24 were used with porous poly(tetrafluoroethylene) (PTFE) film to prepare zirconium hydrogenphosphate (ZrP) hybridized Nafion/PTFE (NF–ZrP) composite membranes by direct impregnating porous PTFE in Nafion/ZrOCl₂ solutions. The influence of [ZrOCl₂]/[Nafion] wt. ratio of Nafion/ZrOCl₂ solution on the membrane morphology of NF–ZrP and polyelectrolyte membrane fuel cell (PEMFC) performance at temperatures of 110–130 °C with relative humidity of 51.7–28.8% RH was investigated.