Polyelectrolyte Nanocomposite Membranes Using Imidazole-Functionalized Nanosilica for Fuel Cell Applications

The preparation and characterization of a new type of nanocomposite polyelectrolyte membrane, based on DuPont Nafion/imidazole-modified nanosilica (Im-Si), for direct methanol fuel cell applications is described. Related to the interactions between the protonated imidazole groups, grafted on the surface of nanosilica, and negatively charged sulfonic acid groups of Nafion, new electrostatic interactions can be formed in the interface of Nafion and Im-Si which result in both lower methanol permeability and also higher proton conductivity. Physical characteristics of these manufactured nanocomposite membranes were investigated by scanning electron microscopy, thermogravimetry analysis, differential scanning calorimetry, Fourier transform infrared spectroscopy, water uptake, methanol permeability, and ion-exchange capacity, as well as proton conductivity. The Nafion/Im-Si membranes showed higher proton conductivity, lower methanol permeability and, as a consequence, higher selectivity parameter in comparison to the neat Nafion or Nafion/silica membranes. The obtained results indicated that the Nafion/Im-Si membranes could be utilized as promising polyelectrolyte membranes for direct methanol fuel cell applications.     

Molecular dynamics simulation study of glass transition in hydrated Nafion

The thermal transition of Nafion is studied using a molecular dynamics simulation through a chemically realistic model. Static and dynamic properties of polymer melts with different water contents are investigated over a wide range of temperatures to obtain viscometric and calorimetric glass transition temperatures. The effect of cooling rate of the simulation on the glass transition of the hydrated polymer is also examined within the well‐known Williams–Landel–Ferry (WLF) equation. Variation of relaxation times versus temperature shows a fragile‐to‐strong transition. The hydration level has a significant impact on the static and dynamic properties of the polymer chains and water molecules confined in nanometric spaces between polymer chains. The results of this study are useful to predict the behavior of Nafion for various applications including fuel cells, sensors, actuators, and shape memory devices at different temperatures. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 907–915     

Determination of Pb and Cu by Anodic Stripping Voltammetry Using Glassy Carbon Electrodes Modified with Mercury or Mercury-Nafion Films

 Two different approaches for the modification of glassy carbon electrodes using a mercury film and mercury-nafion are compared. The mixture of mercury(II) chloride solution with a nafion solution diluted in ethanol is used to coat the polished glassy carbon surface. The modified working electrodes are compared when measuring Pb and Cu in real seawater samples. An optimisation of the parameters during the formation of the films was done to obtain well-defined stripping peaks. The type of inert supporting electrolyte and the pH play an important role on the sensitivity of the measurement. Results for Pb and Cu determinations show the advantages of Hg-nafion modification as an alternative method. These advantages include a shorter modification time, the avoidance of Hg solutions during the formation of the Hg film and an improved sensitivity for Pb determination. Received March 16, 1999. Revision April 24, 2000.     

阳离子交换树脂的有机催化进展

综述了聚苯乙烯型磺酸树脂、全氟磺酸树脂Nafion及崭新的Nafion／siO_2复 合催化剂在有机合成中应用的最新进展．     

Liquid-Phase Selective Oxidation of Propane on Silica-Supported Nafion Catalysts

The liquid-phase partial oxidation of propane in the presence of the Fen+/H2O2 Fenton system at 70℃ and 1.4 atm on silica supported Nafion catalysts has been investigated. The reaction proceeds via a radical reaction path the efficiency of which is improved by silica-supported Nafion catalysts. Because of the direct relationship between reaction rate and concentration of sulphonic acid sites of Nafion catalysts, it is inferred that the active phase enahnces the kinetics of propane conversion by promoting the rate of active radicals generation.     

Benzylation of Aromatic Compounds with Benzyl Chloride Catalyzed by Nafion/SiO_2 Nanocomposite Catalyst

Diphenylmethane and substituted diphenylmethane are important compounds forsynthesis chemistry as well as industrial chemistry. These compounds are easilysynthesized by the benzylation of aromatic compounds with benzyl chloride or benzylalcohol catalyzed by homogeneous acid catalysts, such as AlCl3, FeCl3, H2SO4, HF andBF3. However, these catalytic systems are highly corrosive, and usually proceed withlow selectivity. In addition, they are less satisfactory from the environmen…     

A Novel Amperometric Biosensor for Determination of Hydrogen Peroxide Based on Nafion and Polythionine as Well as Gold Nanoparticles and Gelatin as Matrixes

Abstract

A new biosensor for the amperometric detection of hydrogen peroxide was developed by means of immobilized horseradish peroxidase (HRP) on a platinum disk based on gold nanoparticles, nafion, polythionine (PTn), and gelatin as matrixes. The mediator (PTn) was embedded in nafion film effectively without leaching even after long periods of operation, the immobilization of the enzyme comes from the cooperative binding by the Au nanoparticles and gelatin. The fabrication procedure of the biosensor was characterized by using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The electrochemical characteristics of the enzyme electrode with respect to the effect of pH, temperature, and the operational and storage stabilities were studied. The test demonstrated that the biosensors show high stability, fast response (<20 s), and a working range 0.05 to 30.6 mM (correlation coefficient: 0.9986), a detection limit of 0.02 mM to hydrogen peroxide (H₂O₂). The analytical results by this approach were in satisfactory agreement with those by conventional methods of titration.     

Highly transparent and flexible field electron emitters based on hybrid carbon nanostructure

We demonstrate a unique strategy to fabricate highly transparent and flexible field electron emitters (FEEs) based on combined carbon nanostructures, i.e., conical nanocarbon structures (CNCSs) and single‐walled carbon nanotubes (SWNTs). The combined structure was prepared by spray coating of 1,2‐dichloroethane (DCE) dispersed SWNTs onto neon ion (Ne⁺) irradiation induced CNCSs on nafion substrate. The field emission (FE) property of SWCNTs on both flat nafion and CNCSs surfaces increased with increasing the SWCNTs amount. The best FE result was attained for the highest amount of SWCNTs on the CNCSs substrate. This kind of collective structures is found to be effective emitters on transparent and flexible ion‐irradiated nafion substrate. Moreover, the combined carbon nanostructures showed improved transparency and emission performance compared to the individual nanostructures. The FE properties of 0.5 ml SWCNTs solution on CNCSs surfaces were equal to those of 1.5 ml SWCNTs solution on flat nafion surface. The hybrid structure based emitters (CNCSs and SWCNTs) produced by this method are lower‐cost cathode materials than hybrid structures of SWCNTs and flat nafion. Thus the combined nanostructures of SWCNTs/CNCSs might have huge prospects for the fabrication of efficient transparent and flexible FEEs and their broad application in next‐generation portable display devices. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Ionophore Based Bismuth Film Electrode for Lead

Abstract

A Nafion/ionophore, 4-tert-butylcalix[4]arene-tetrakis(N,N-dimethylthioacetamide) composite coated and bismuth film modified glassy carbon electrode. (GC/NA-IONO/BiFE) was described to determine trace lead sensitively and selectively. The characteristics of such modified GC/NA-IONO/BiFE were studied by scanning electron microscopy and cyclic voltammetry. The influence of various experimental parameters upon the stripping lead signal at the GC/NA-IONO/BiFE was explored. Under the optimized conditions, the differential pulse voltammetric stripping response is highly linear over the 0.1–8.0 nM lead range examined (180 s preconcentration at ?1.2 V), with a detection limit of 0.044 nM and good precision (RSD = 5.4% at 0.5 nM). Also applicability to seawater samples was demonstrated at such modified electrode. The high selectivity of ionophore coupled with the excellent electrochemical characteristics of bismuth endow the GC/NA-IONO/BiFE a promising and robust tool for monitoring of trace lead rapidly and precisely.     

Synthesis and Ex-situ Characterization of Nafion/TiO2 Composite Membranes for Direct Ethanol Fuel Cell

Nafion/TiO₂ composite membranes for different loadings of TiO₂ were prepared by casting method for the possible application in direct ethanol fuel cell (DEFC). The properties of the composite membranes were investigated by scanning electron microscopy (SEM), x-ray diffraction (XRD), thermogravimetric analyser (TGA), ion exchange capacity, water and alcohol uptake, swelling ratio, proton conductivity, and ethanol crossover. The observed characteristics of the membranes were evaluated for DEFC and compared with the direct methanol fuel cell (DMFC) membrane. The analysis reveales a significant influence on the TiO₂ surface characteristics, water and alcohol uptake, and swelling of the membrane. The TiO₂ composite membranes exhibited a sharp decrease in methanol and ethanol crossover for 5% TiO₂ and the proton conductivity was heighest for 1% TiO₂ loading. The best compromise between proton conductivity and crossover has been found out with the help of the characteristic factor ϕ. The optimum loading of 5% TiO₂ composite membrane has shown the maximum characteristic factor.