Structuring in the formation technology of electrode material based on nafion proton-conducting polymer and thermally expanded graphite containing platinum nanoparticles on carbon black

Laboratory production technique is described for fabrication of an electrode material containing platinum nanoparticles on carbon black, proton-conducting polymer Nafion, and thermally expanded graphite for direct-energy-conversion systems (fuel cells, electrolyzers, electrochemical sensors). Results of a study of the material by differential thermal analysis are presented. Scanning and transmission electron microscopy was used to examine the structure of the material, and its elemental composition was determined by the EDX method. Dependences of the porosity of the material on its composition are presented.     

Technology and structural characteristics of electrode material in the Pt/C–Taunite-MD–Nafion system

Laboratory technique was developed for fabrication of an electrode material containing a platinized carbon black, carbon nanofibers, and proton-conducting polymer Nafion. Scanning and transmission electron microscopy was used to study the structure of the material and experimental dependences were obtained that relate the properties and structure of the electrode material to its structure and fabrication technique and make it possible to obtain a material with prescribed service characteristics.     

Amperometric biosensor based on thermally activated polymer-stabilized metal nanoparticles

Polymer-stabilized Pd nanoparticles on carbon support were synthesized by a low thermal procedure that does not involve the utilization of a reducing agent such as NaBH₄ or hydrogen gas for the formation of the metallic nanoparticles. The Pd-catalyzed graphite particles were then mixed with known amounts of glucose oxidase (GOx) enzyme and Nafion to prepare a GOx-immobilized ink. A glassy carbon electrode (GCE) modified with the GOx ink was used to evaluate the performance of the biosensor electrode. The results of TEM and AFM show that the Pd nanoparticles are uniformly distributed on top of the substrate. Results are presented for sensing glucose through the voltammetric measurement of H₂O₂. Coupled with the simplicity of preparation, the biosensor exhibited high sensitivity and extended linear range for glucose measurement. Further, the electrochemical characteristics of the nanocomposite biosensor were evaluated with respect to the electrochemistry of potassium ferricyanide by cyclic voltammetry. Whereas the presence of polymer and Nafion improved the stability of both the ink and biosensor electrode, the concentration of glucose was measured without interferences from oxygen, ascorbic acid and uric acid because of the Nafion.     

Thermal Degradation of Nafion in the Presence of Nanostructured Materials: Thermally Expanded Graphite,Carbon Black,and Platinum

Russian Journal of Applied Chemistry - Thermal degradation in air of Nafion proton-conducting polymer in composites containing nanostructured carbon materials [carbon black of Vulcan XC-72 grade...     

Effect of carbon nanostructures on the carbonization of polyacrylonitrile

Composite materials based on polyacrylonitrile with carbon nanofillers (technical-grade carbon, thermally expanded graphite, carbon nanotubes) were synthesized. A carbonization of film and fiber composite samples in the temperature range 20–1000°C provided a noticeable increase in the thermal stability of fibers and a rise in the electrical conductivity of the composite material. Dependences of the degree of carbonization on the concentration of nanostructures, type of material, and nature of modifier were determined. Differential-thermal and X-ray diffraction analyses revealed the formation of oriented nucleus structures of turbostratic carbon in the temperature range 450–550°C.     

Customized Bio‐functionalization of Nanocomposite Carbon Paste Electrodes for Electrochemical Sensing: A Mini Review

Over the past few decades, the (bio)functionalization of carbon nanomaterials (CNMs), such as nanohorns, carbon nanotubes, graphene, graphite and related with a wide range of (bio)modifiers have been extensively studied for their incorporation on different pure metal or carbon electrode surfaces via drop‐casting. However, CNMs are also shown to be important functional additives for polymers, having great potential to produce rigid nanocomposite materials with a range of enhanced properties, including mechanical, optical, electrical, thermal and electrochemical. The high malleability derived from the host polymer allows alternative strategies that can be carried out in order to incorporate different types of (bio)modifiers in/on/into a polymeric nanocomposite electrode. Accordingly, this mini review overviews the main methodologies used for the bio‐functionalization of electrochemical transducers based on nanocomposite carbon paste electrodes (NC‐CPEs). Additionally, the most extensively (bio)modifiers used in electrochemical (bio)sensing, together with their various electrocatalytical performance are also discussed, fact that might serve as a general outlook for planning further research.     

Interaction of Water and Methanol Molecules with the Surface of Carbonaceous Materials According to Gas Chromatographic Data

We have used gas chromatography to study the interaction of water and methanol molecules with active hydrophilic centers on the surface of thermally expanded graphite and graphitized thermal carbon black. We have determined the concentration of carboxyl and phenol hydroxyl groups on the surface of the sorbents and the heats of adsorption for adsorption of the studied substances on these groups. We have shown that water molecules are adsorbed as clusters on the hydrophilic centers of the studied sorbents at very low relative pressures, with n = 2 molecules in the cluster.     

Stability of electrical and mechanical properties of polyethylene/carbon black composites

The stability of electrical and mechanical properties of two kinds of polymer composites ‐ polyethylene/carbon black and polyethylene/carbon black modified by polypyrrole ‐ was investigated during slow cycle heating and cooling. Conductivity in composites was measured in heating/cooling cycles in the temperature range from 16°C to 125°C. It was found that the thermal treatment resulted in the conductivity changes and the mechanical properties of treated composites have also been influenced. The effect was explained by increased crystallinity in the polymer matrix of thermally treated composites.     

Cuprous Oxide/Nitrogen-doped Graphene Nanocomposites as Electrochemical Sensors for Ofloxacin Determination

Cu₂O/nitrogen-doped grapheme(NG) nanocomposite material was prepared via a facile one step chemical reduction and characterized by means of X-ray diffraction(XRD) and scanning electron microscopy(SEM). A new electrochemical sensor was then fabricated by coating Cu₂O/nitrogen-doped graphene nanocomposite with Nafion on glassy carbon electrode(Cu₂O/NG/Nafion/GCE). The electrochemical response of this modified electrode toward ofloxacin was examined by cyclic voltammetry. The results indicate that Cu₂O/NG/Nafion composite-modified electrode exhibits higher catalytic activity in the electrochemical oxidation of ofloxacin compared with glassy carbon electrode(GCE), Cu₂O/Nafion modified electrode(Cu₂O/Nafion/GCE), and N-doped graphene/Nafion modified electrode(NG/Nafion/GCE). Under optimal conditions, the peak current was found to be linearly proportional to the concentration of ofloxacin in the 0.5-27.5 μmol/L and 27.5-280 μmol/L ranges with a lower detection limit of 0.34 μmol/L, higher sensitivity of 39.32 μA·L·mmol^-1 and a shorter reaction time of less than 2 s. In addition, Nafion can enhance the stability of the modified electrode and prevent some negative species. Thus the modified electrode exhibits good selectivity and a long working life. The Cu₂O/NG/Nafion composite modified electrode shows promising application in electrochemical sensors, biosensors, and other related fields because of its excellent properties.     

Electrocatalytic Properties of a Composite Based on Cobalt Porphyrin Pyropolymer and Nafion

Methods for the formation of composite polymer materials that comprise cobalt porphyrin pyrolized on carbon black and a proton-conducting polyelectrolyte, are proposed. Electrocatalytic activity of these materials in the cathodic reduction of oxygen in a free sulfuric acid electrolyte is studied using a floating gas diffusion electrode and a rotating electrode.     

Pyropolymer-based Oxygen Electrode for Solid Polymer Electrolyte Systems

The activity of composite materials (acetylene black or ultrafinely divided dynamic diamond + Co-pyropolymer + Nafion solution) in the oxygen electroreduction in a 0.5 M H₂SO₄solution and when using a Nafion-117 film 200 m thick as a proton-conducting electrolyte is compared. It is established that the addition of Nafion in the active mass leads to a decrease in the electrocatalytic activity of the latter. The same composite catalyst (at an insignificant thickness of the active layer) in contact with a solid polymer electrode makes it possible to obtain current densities ten times those in a sulfuric acid solution. Possible reasons for these effects are discussed.     

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.     

Thermally expanded graphite: Synthesis, properties, and prospects for use

Results obtained in synthesis of thermally expanded graphite by chemical and electrochemical methods with sulfuric and nitric acids are summarized. The possibility of controlling the properties of thermally expanded graphite compounds in electrochemical synthesis is demonstrated. The existing and promising application areas of thermally expanded graphite are analyzed.     

Thermal degradation of epoxy composites based on thermally expanded graphite and multiwalled carbon nanotubes

Thermal degradation of epoxy composites filled with various carbon materials (thermally expanded graphite, multiwalled carbon nanotubes) was studied. The dynamics of the thermal degradation of epoxy composites was evaluated by thermogravimetric analysis in the temperature range of 55–700°С (heating rate 10 deg min^–1) in an oxidizing medium. Carbon fillers were studied by scanning electron microscopy, transmission electron microscopy, and low-temperature nitrogen adsorption. The influence of the composite preparation procedure on its thermal stability was determined. The type of filler significantly influences the thermal oxidative degradation of the composites.     

Structure and Properties of Polymer Biocomposite Materials

Results of studying the structure and properties of biocomposite materials are summarized. The materials in question include an enzyme (laccase, peroxidase), an ion- or electron-conducting polymer (Nafion, polymethylpyrrole), and a carbon substrate (compact, disperse). It is shown that the orientation of a large number of enzyme molecules in an enzyme/Nafion composite material on the substrate surface favors direct bioelectrocatalysis. During co-immobilization of an enzyme and polymethylpyrrole, conditions are realized under which the polymer takes part in the electron transfer between the active center of the enzyme and the surface of the electroconducting substrate. A fresh approach to constructing a biocomposite material is developed. The material is based on an extremely finely divided carbon material (colloidal graphite), which ensures a high specific activity of laccase immobilized on it. The size of colloidal-graphite particles is commensurate with that of the laccase molecule, owing to which the enzyme macromolecule is surrounded by carbon particles. As a result, practically all adsorbed enzyme molecules are electrochemically active and participate in direct bioelectrocatalysis.     

Polymeric bilayer modified microelectrodes for in-vivo determination of neurotransmitter dopamine

A composite polymer carbon fiber electrode modified with Nafion and cellulose acetate is described.The modified electrode discriminates against both anionic reactants and big molecular organic compounds.The bilayer configuration is prepared in two steps.First,the carbon fiber electrode is coated with Nafion,then followed by air evaporation of the solvent,the electrode is dipped in a cellulose acetate solution and hydrolyzed for a selected time.The permeability of the film is explored by use of rotating disk electrode measurements.Parameters affecting the film electrochemistry are investigated.The resulting electrodes show high selectivity and stability in body fluids.For in-vivo voltammetry,the composite polymer modified electrode has been used for detection of the oxidative current of neurotransmitter dopamine in rat brain,while it inhabits the oxidation of anionic neurotransmitter metabolites and some electroactive compounds.     

石蜡/膨胀石墨/石墨烯复合相变储热材料的制备及性能

以石蜡(PA)作为相变储热材料、 膨胀石墨(EG)作为主导热材料和支撑材料, 石墨烯气凝胶(GA)作为导热增强材料和辅支撑材料制备了PA/EG/GA复合相变材料, 研究了GA添加量对复合相变材料相变温度、 相变潜热、 导热性能以及循环稳定性的影响. 结果表明, 所制备的80%PA-17%EG-3%GA复合相变材料导热性能良好, 循环稳定性出色. 与80%PA-20%EG复合材料相比, 该材料的相变温度、 相变潜热以及循环稳定性无明显变化, 但导热系数由4.089 W/(m·K)提升到了5.336 W/(m·K), 显示出良好的应用前景.     

Improved Nafion-based amperometric sensor for hydrogen in argon

An improved polymer electrolyte membrane fuel cell-based amperometric hydrogen sensor has been developed. The sensor operates at room temperature, and the electrolyte used in the sensor is Nafion which is a proton-conducting solid polymer electrolyte. Platinum black is used as both anode and cathode. The sensor functions as a fuel cell, H₂/Pt//Nafion//Pt/O₂, and a mechanical barrier limits the supply of hydrogen to the sensing side electrode. The limiting current is found to be linearly related to the hydrogen concentration. The sensor can be used to measure hydrogen in argon in parts per million and percentage levels. The basic principle, details of assembly, and response behavior of the sensor are discussed.     

A simple Maxwell-Wagner-Butler-Volmer approach to the impedance of the hydrogen electrode in a nafion fuel cell

A simple one-dimensional model of the impedance of a hydrogen/Nafion electrode is set up combining the usual Maxwell-Wagner approach for linear, homogeneous, and isotropic media with the linearized Butler-Volmer equation for the interfacial, electrochemical reaction. Only one relaxation semicircle is normally seen in the Nyquist diagram, but a low-frequency arc may appear at high overvoltages. The model is described by only two dimensionless parameters (in addition to the dimensionless frequency). These parameters are related to the double-layer capacitance and to the interfacial electrochemical reaction rate, respectively. With some adjustments, the model can be used to explain the observed equilibrium impedance from 40 to 70 degrees C of a symmetric cell of the type C/Pt/H(2)|Nafion 117/H(2)/Pt/C. The hydrogen electrodes in this cell were built up as a disperse multiphase region (carbon, platinum grains, Nafion 117, and hydrogen gas) as commonly done in solid polymer fuel cells.