Degradation mechanism of polystyrene sulfonic acid membrane and application of its composite membranes in fuel cells

The lifetime behavior of a H-2/O-2 proton exchange membrane (PEM) fuel cell with polystyrene sulfonic acid (PSSA) membrane have been investigated in order to give an insight into the degradation mechanism of the PSSA membrane. The distribution of sulfur concentration in the cross section of the PSSA membrane was measured by energy dispersive analysis of X-ray, and the chemical composition of the PSSA membrane was characterized by infrared spectroscopy before and after the lifetime experiment. The degradation mechanism of the PSSA membrane is postulated as: the oxygen reduction at the cathode proceeds through some peroxide intermediates during the fuel cell operation, and these intermediates have strong oxidative ability and may chemically attack the tertiary hydrogen at the a carbon of the PSSA; the degradation of the PSSA membrane mainly takes place at the cathode side of the cell, and the loss of the aromatic rings and the SO3- groups simultaneously occurs from the PSSA membrane. A new kind of the PSSA-Nafion composite membrane, where the Nafion membrane is bonded with the PSSA membrane and located at the cathode of the cell, was designed to prevent oxidation degradation of the PSSA membrane in fuel cells. The performances of fuel cells with PSSA-Nafion101 and PSSA-recast Nafion composite membranes are demonstrated to be stable after 835 h and 240 h, respectively.

Theoretical study on the mechanism of the reaction of CH4+MgO

The reactions of (1) CH4 + MgO --> MgOH. + CH3. and (2) CH4 + MgO --> Mg + CH3OH have been studied on the singlet spin state potential energy surface at the MP2/6-311+G(2d,2p) level. These two reaction channels, both involving intermediates and transition states, have been rationalized by the structures of the species involved, natural bond orbital (NBO), and vibrational frequency analysis. We have considered two initial interacting models between CH4 and MgO: a collinear C-H approach to the O end of the MgO forming the MgOCH4 complex with C-3nu symmetry and three hydrogen atoms of the methane point to the Mg end of the MgO forming the OMgCH4 complex with C-1 symmetry. The calculations predict that reactions 1 and 2 are exothermic by 39.8 and 86.5 kJ mol(-1), respectively. Also, the former reaction proceeds more easily than the latter, and the complex HOMgCH3 is energetically preferred in the reaction of MgO + CH4.

The mechanism studies of ethanol oxidation on PdO catalysts by TPSR techniques

The paper studies the direct oxidation of ethanol and CO on PdO/Ce0.75Zr0.25O2 and Ce(0.75)Zr(0.2)5O(2) catalysts. Characterization of catalysts is carried out by temperature-programmed desorption (TPD), temperature-programmed surface reaction (TPSR) techniques to correlate with catalytic properties and the effect of supports on PdO. The simple Ce0.75Zr0.25O2 is in less active for ethanol and CO oxidation. After loaded with PdO, the catalytic activity enhances effectively. Combined the ethanol and CO oxidation activity with CO-TPD and ethanol-TPSR profiles, we can find the more intensive of CO2 desorption peaks, the higher it is for the oxidation of CO and ethanol. Conversion versus yield plot shows the acetaldehyde is the primary product, the secondary products are acetic acid, ethyl acetate and ethylene, and the final product is CO2. A simplified reaction scheme (not surface mechanism) is suggested that ethanol is first oxidized to form intermediate of acetaldehyde, then acetic acid, ethyl acetate and ethylene formed going with the formation of acetaldehyde, acetic acid, ethyl acetate; finally these byproducts are further oxidized to produce CO2. PdO/Ce0.75Zr0.25O2 catalyst has much higher catalytic activity not only for the oxidation of ethanol but also for CO oxidation. Thus the CO poison effect on PdO/Ce0.75Zr0.25O2 catalysts can be decreased and they have the feasibility for application in direct alcohol fuel cell (DAFC) with high efficiency.

A simple preparation of stationary phase of alkylamide reversed-phase liquid chromatograph for the separation of basic substances

A simple preparation process of alkylamide phase for reversed-phase HPLC (RP-HPLC) is described. The process includes aminopropyltrimethoxysilane firstly reacted with octanoyl chloride, then the intermediate was coupled onto porous silica. The resultant bonded silica has a reproducible ligand surface concentration and homogenous bonded ligand distribution on the porous silica. Characterization of prepared packing was carried out with elemental analysis, solid-state C-13 NMR and Fourier transform infrared (FT-IR). Chromatographic evaluations were carried out by using a mixture of organic compounds including acidic, basic and neutral analytes under methanol/water as binary mobile phase. The results showed that the stationary phase have excellent chromatographic properties and can be efficiently used for the separation of basic compounds.

Dimerization of 1-butene via zirconium-based Ziegler-Natta catalyst

A zirconium-based Ziegler-Natta catalytic system has been tested in the dimerization of 1-butene. It was found that the concentration of Et2AlCl, Ph3P and PhONa as well as the reaction temperature had great influences on the activity and selectivity of the catalyst. Under the optimum reaction conditions, the conversion of 1-butene is 91.9%, and the selectivity of dimers is 76.7%. Basic ligands such as Ph3P and PhONa can inhibit isomerization of 1-butene to 2-butene effectively. In addition, the metal hydride mechanism was also suggested and some indirect evidence was obtained in favor of this mechanism.

adaptive location update mechanism for network-constrained moving objects in changeful traffic conditions

Natl Chiao Tung Univ, Dept Comp Sci

挖掘作物抗旱节水潜力——作物对多变低水环境的适应与调节

本文针对半干旱地区多变低水的实际田间环境,讨论了作物对不同干旱类型的反应,适度干旱后复水的生理补偿效应,不同类型作物在干湿交替条件下的差异,以及增强作物对多变水环境适应的技术.同时,就多变低水环境的概念、作物对多变低水环境的适应机理以及作物抗旱生理研究与旱农生产实际相衔接等问题提出了若干看法.

农牧交错区生态环境恢复与重建的可持续发展思路

根据草地和农牧交错区生态系统重建机理及优化生态—生产模式国家重点基础研究发展规划的要求 ,综合分析了我国农牧交错区的基本现状 ,系统论述了农牧交错区存在的草地“三化”突出、农业生产低下、自然灾害频繁等问题 ,研究和寻求生态系统退化、恢复和重建的关键技术与途径 ,进一步探讨在西部大开发中农牧交错区的发展思路。

植物化感作用与生物多样性

本文简要地阐释了化感作用的含义、基本特征以及作用机制,并结合生物多样性理论,综述了化感作用研究中化感物种的多样性、化感物质的多样性及其释放途径的多样性,具体讨论了化感作用对物种多样性、遗传多样性及生态系统多样性中的种群生态、协同进化、土壤生境、生态系统功能和生物入侵等方面的可能影响。文中提出了化感作用的利用、管理应与生物多样性保护相统一的看法,并指出对化感作用与生物多样性的关系以及相互影响机制进行本质的探索,特别是对植物化感作用的生态服务功能与价值评估与探讨,可为保护生物学和系统生态学提供理论基础,这也是今后工作开展的一个重要方向。

an integrity assurance mechanism for run-time programs

Chinese Assoc Cryptol Res, State Key Lab Informat Secur, Inst Software, Grad Univ Chinese Acad Sci, Natl Nat Sci Fdn China