Theoretical analysis of the performance of a model supercapacitor consisting of metal oxide nano-particles

The factors influencing the electrochemical behaviour of a supercapacitor have been partly examined in this work. The effects of so-called intrinsic parameters, i.e. exchange current density, unit cell length and double layer (DL) capacitance; as well as the so-called application parameters, i.e. cell current, on the cell potential discharge time have been considered. The contributions of each type of capacitors, DL capacitor and faradaic supercapacitor under various states of operation and material have been analyzed, and the competing (compensating) effects of the two types of capacitors as regards to the discharge and power characteristics manifested by current–potential and energy–power (Ragone plots) are elucidated.     

A Procedure for Transforming Impedance Spectra for the Determination of Mechanism of Electrochemical Reactions

Transformation of impedance spectra into relaxation time spectra (RTS) is used for determining contributions of individual processes of the oxygen electroreduction reaction (OER) to the polarization resistance of the electrochemical cell. The transformation technique involves the solution of the convolution equation found with the aid of a modified Van Cittert iteration algorithm checked on model impedance spectra. The technique, when used to analyze impedance spectra of electrochemical cells air|Pt|YSZ|YSZ + Pt|air, shows that the conversion of a globular structure of the YSZ + Pt cermet layer to a columnar one is accompanied by a change of peak amplitudes in RTS. The revealed RTS dynamics when heated to 750°C is compared with peculiarities of individual processes in OER.     

碳纳米管添加剂对质子交换膜燃料电池低铂载量膜电极性能的影响研究

以碳纳米管（CNT）作为低铂载量膜电极（CCM）催化层（0.1 mg_Pt·cm^-2）添加剂，研究了CNT的添加方式对催化层微观结构以及膜电极性能的影响.结果表明，与常规低铂载量催化层相比，在其表面喷涂一层CNT或将CNT均匀分散到Pt/C催化层中均有利于提升低铂载量膜电极的输出性能，在70℃和100%相对湿度条件下最高输出功率比常规低铂载量膜电极的0.522 W·cm^-2分别提升了22.4%和60.0%，并且均匀分散添加方式优于分层添加方式.其原因在于分层添加CNT后改善了低铂催化层和气体扩散层之间的接触界面，降低了催化层与扩散层间的接触电阻，而均匀分散添加方式除了可降低界面接触电阻外，还显著改善了低铂催化层中的气体传输，大幅提升了Pt催化剂的利用效率，使得膜电极电化学反应电阻明显降低.进一步对均匀分散添加方式中CNT的载量进行优化，表明CNT添加量为37.5 μg·cm^-2时电池输出性能最佳，70℃和100%相对湿度条件下的最大输出功率达到0.91 W·cm^-2.本研究工作表明，将CNT均匀分散添加到催化层中是一种有效提升低铂载量膜电极性能的方法.     

Cathode of a fuel cell with a solid polymer electrolyte: Calculating overall currents in the presence of a gas-diffusion layer

Mathematical apparatus, which makes it possible to perform calculations of the current-voltage characteristics of cathodes of fuel cells with a solid polymer electrolyte in conditions where there are present extraneous diffusion restrictions is proposed. In so doing, the partial pressure of oxygen and the absolute pressure of gas in the gas chamber may assume any values. First of all presented are the results of calculations of the current-voltage characteristics intrinsic to active layers of the air and oxygen cathodes, which are performed under the assumption that the extraneous diffusion restrictions are absent altogether. Thereafter, in the same conditions (at the same parameters that characterize the active layer of a cathode), obtained are results of a calculation of the current-voltage characteristics inherent in the air and oxygen cathodes in the presence of extraneous diffusion restrictions. Afterward there is performed an analysis of the way a gas-diffusion layer restricts the process of generation of current in a cathode and of what measures should be taken in order for the extraneous diffusion restrictions to become less significant.     

无烟煤结构的高分辨电镜研究

镜质组不仅是煤结构变化最具规律性，也是影响煤质的主要微成分。用点分辨率为２．１Ａ的高分辨电镜对几种不同煤化程度的无烟煤大分子结构进行了研究。结果表明：电镜图像直接表征了无烟煤分子的非均匀性孔隙结构。京西煤分子方向化程度强，主要以芳层平行堆或有序化前结构为主；晋城煤方向化程度弱，主要以粒状嵌晶结构为主。高分辨电镜技术是研究煤分子结构和煤化作用实质的有效方法。     

A novel technique to measure the surface electrical potential of polymer films by using dielectric spectroscopy

A novel method that allows the determination of the electrical potential of a polymer surface has been applied for polypropylene film treated by N₂ + H₂ cold plasma. The plasma treatment results in formation on the film surface of NH₂ groups, which then gets transformed to NH₃⁺ in contact with an electrolyte and leads to the formation of an electrical double layer. The method consists of theoretical calculation of electrical model potential, using the measurement of the electrical capacitance of the film in contact with an electrolyte by dielectric spectroscopy. Comparison with the results obtained by theoretical model shows similar dependencies of the electrical potential as a function of amino‐groups density and electrolyte concentration, but systematic differences of absolute values are observed. Copyright © 2005 John Wiley & Sons, Ltd.     

Low dielectric thermoset. II. Synthesis and properties of novel 2,6‐dimethyl phenol–dipentene epoxy

A 2,6‐dimethyl phenol–dipentene adduct was synthesized from dipentene (DP) and 2,6‐dimethyl phenol, and then a 2,6‐dimethyl phenol–DP epoxy was synthesized from the reaction of the resultant 2,6‐dimethyl phenol–DP adduct and epichlorohydrin. The proposed structures were confirmed by Fourier transform infrared, elemental analysis, mass spectra, NMR spectra, and epoxy equivalent weight titration. The synthesized 2,6‐dimethyl phenol–DP adduct was cured with 4,4‐diamino diphenyl methane, phenol novolac, 4,4‐diamino diphenyl sulfone, and 4,4‐diamino diphenyl ether. The thermal properties of the cured epoxy resins were studied with differential scanning calorimetry, dynamic mechanical analysis, dielectric analysis, and thermogravimetric analysis. These data were compared with those for the bisphenol A epoxy system. The cured 2,6‐dimethyl phenol–DP epoxy exhibited a lower dielectric constant (ca. 3.1), a lower dissipation factor (ca. 0.065), a lower modulus, lower thermal stability (5% degradation temperature = 366–424 °C), and lower moisture absorption (1.21–2.18%) than the bisphenol A system but a higher glass‐transition temperature (ca. 173–222 °C) than that of bisphenol A system. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4084–4097, 2002     

Topical Problems in Elemental Analysis of Advanced Ceramic Materials

Selected prominent problems in the analysis of advanced ceramic materials are surveyed. The importance of reliability of results is discussed in the field of elemental trace- and microanalysis in view of its interaction with economy, power of detection, local resolution and speciation selectivity. Particular problems in the analysis of major constituents, trace components and microlocal distributions are based on the striking propertics of ceramics; they are exemplified. Analytical assistance must start from the beginning of the production processing, in the preparation of the powdered base materials. Determination of the stoichiometry requires high accuracy and differentiation of chemical species in bulk and surface analysis of ceramic base powders. Element trace determination by direct instrumental methods requires standard reference materials for calibration; these are currently inavailable in a sufficient variety. For optimum reliability and power of detection, element traces must be prepared in isolated form in a small excitation volume for analysis. A review on the state-of-the-art of wet-chemical combined procedures is presented. Decomposition position procedures are emphasized, due to their risk of contributing severe systematic error. Combustion in elementary fluorine is presented for decomposition of refractory materials. The performance of some direct procedures is discussed. Very efficient methods are available for element trace determinations in ceramic materials, offering high detection power. Several approaches for high-resolution local microanalysis in non-conductive ceramic materials are identified as the most promising development in the analysis of sintered compact ceramic products and devices.     

Oxidation of Styrene in a Silent Discharge Plasma

A silent discharge plasma reactor has been developed to study the oxidation of styrene vapor in argon/oxygen mixtures. A number of analytical techniques were employed to determine the destruction efficiency and to characterize the intermediate products. The destruction efficiency was measured as a function of initial styrene concentration, temperature, and energy density of the plasma. The formation of solid products was observed in most experiments. At low temperature (100°C), the solid deposit was polymeric in nature, while at high temperature (300°C) the solid appeared to be amorphous carbon. A combination of high temperature and high energy density resulted in high destruction efficiency and minimal production of solid films. The destruction efficiency vs. energy density is shown to be more complex than a simple model predicting exponential behavior. Several reasons for the discrepancy are suggested. The e-folding energy density for the destruction of styrene is compared to literature values for other organic compounds, measured using similar types of plasma reactors.     

Synthesis of three-layered titanates BaLn<Subscript>2</Subscript>Ti<Subscript>3</Subscript>O<Subscript>10</Subscript> in systems with coprecipitated hydroxocarbonates

The synthesis of three-layered titanates BaLn₂Ti₃O₁₀ (Ln = La, Nd, Sm) in systems with coprecipitated hydroxocarbonates was studied. It was established that they are formed through an intermediate phase with a defective perovskite structure followed by its transformation into the three-layered structure by the ordering of vacancies and rare-earth element and barium atoms and subdivision into three-layered blocks. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 6, pp. 349–353, November–December, 2007.