Physical and morphological characteristics and electrochemical behaviour in PEM fuel cells of PtRu /C catalysts

Platinum-ruthenium catalysts supported on carbon (PtRu/C) have been characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), specific surface area analysis (BET), X-ray photoelectron spectroscopy (XPS) and in proton exchange membrane (PEM) fuel cell tests. The results indicate the presence of strong metal-carbon interactions, which hinder the formation of a single-phase face-centered cubic (fcc) PtRu alloy. The particle size of the PtRu/C catalysts was smaller than both carbon-supported platinum (Pt/C) and ruthenium (Ru/C) catalysts. In the bimetallic electrocatalysts the intercrystallite distance decreased with respect to pure Pt and Ru metals. PEM fuel cell tests in H₂/air operation mode revealed a decrease of performance with increasing carbon content of the catalyst, at a fixed Pt loading. In H₂ + 100 ppm CO/air operation mode the maximum performance of the PEM fuel cell was attained at 0.63 atomic fraction Ru. Received: 2 December 1999 / Accepted: 27 January 2000     

Ageing of magnesium /manganese dioxide primary cells

Mg/MnO₂ primary cells which were more than a decade old were investigated for their discharge capacity, a.c. impedance behaviour, delay time, effect of added water into the cell and effect of temperature. Although the cells were aged for a long duration, they were electrochemically active and yielded good discharge capacity, thus suggesting an extraordinary long shelf-life. There was a marginal increase in cell capacity subsequent to injection of 2 ml of water into a CD-size Mg/MnO₂ cell. The a.c. impedance of a partially discharged cell included the contributions of surface passive film on the Mg anode and corrosion of the Mg metal. The internal resistance of the cell was found to increase with storage time, suggesting that the resistance of a fresh cell also could similarly increase. By increasing the cell temperature, the impedance decreased considerably and also the delay time. These results suggested that the increase of temperature had favourable effects on the performance of the aged Mg/MnO₂ cells. Received: 24 August 1999 / Accepted: 2 December 1999     

Optimal Base Station Positioning and Channel Assignment for 3G Mobile Networks by Integer Programming

In this paper, discrete mathematical programming approaches are used to solve the frequency allocation and cell site selection problem in an integrated setup. Both CDMA (code division multiple access) and FD/TDMA (frequency/time division multiple access) technologies will be important for 3rd generation mobile systems. If all users share the same bandwidth, base transmitter stations should be placed such that a maximum of traffic can be carried at low interference rates. The expected traffic is represented by spatially scattered weighted nodes. The problem to select an optimal set of base station locations from a given pool of configurations is formulated as an integer linear program and solved by combinatorial optimization methods. For systems which employ FD/TDMA schemes, the cell site optimization process depends on the assignment of channels. We suggest an integrated linear programming approach to solve both objectives in a single planning step. Because of the problems' tremendous complexity, special branch-and-bound procedures are developed as exact and approximate solution methods. An examples is given for a typical urban scenario with base transmitters below roof tops.     

Correlation of counterions with rodlike macroions as assessed by anomalous small-angle X-ray scattering

We consider the analysis of a rodlike synthetic polyelectrolyte in solution by anomalous small-angle X-ray scattering (ASAXS) in order to elucidate the correlation of the counterions with the highly charged macroion. ASAXS can be applied to these systems because the absorption edge of typical counterions, for example, bromine or iodine ions can be attained by synchrotron radiation. Model calculations using the Poisson–Boltzmann cell model show that ASAXS furnishes two terms caused by the anomalous dispersion of the counterions. The leading terms is a cross-term between the ordinary scattering amplitude of the polyelectrolyte and the real part of the scattering length f ′ of the counterions. A second term refers solely to the anomalous contribution of the counterions, i.e., to f ′ and f ′′ ( f ′′: imaginary part of scattering length). Preliminary data obtained from rodlike synthetic macroions having iodine counterions corroborate the theoretical deductions. They demonstrate that ASAXS is capable of furnishing information that is not available by the ordinary SAXS experiment. Received: 11 December 2000/Accepted: 22 February 2001     

Influence of selenium on the catalytic properties of ruthenium-based cluster catalysts for oxygen reduction

The favourable influence of selenium on the catalytic properties of Ru-based catalysts for the oxygen reduction reaction in acid electrolytes has been investigated by rotating disk electrode measurements. Compared to the oxygen reduction of selenium-free Ru-based catalysts, the overpotential at low current densities (ca. 10 μA cm⁻²) is not affected by the presence of selenium whereas selenium-containing catalysts show higher current densities under fuel cell relevant conditions. The kinetically controlled current density at 0.6 V versus SHE increases 4–5 fold with increasing selenium content. A maximum value is obtained at about 15 mol% Se. This effect is tentatively explained by a modification of the catalytic active centre, which is assumed to consist of Ru---C---CO complexes. IR spectroscopic investigations indicate a reaction of selenium with these complexes. This model is also supported by the study of the electrooxidation of CO. In contrast to the selenium-free catalyst, no CO oxidation is observed on the selenium-containing catalyst. Additional effects of selenium are an enhanced stability towards electrochemical oxidation and a lower amount of Ru oxides formed during synthesis, as evidenced from XRD investigations. Direct four electron oxygen reduction to water is efficient and H₂O₂ production of these catalysts is small (about 5% at potentials <0.3 V vs. SHE ).     

Pressure Dependence of the Lattice Distortion in Perovskite La0.5−xBixCa0.5MnO3 (x=0.1, 0.15, 0.2)

The in situ behavior of distorted perovskite La_0.5−xBi_xCa_0.5MnO₃ (x=0.1, 0.15, 0.2) under high pressure has been studied by energy-dispersive X-ray diffraction in a diamond anvil cell. An abnormal change of the 202–040 d-spacing ascribed to the disappearance of the distortion mode Q₂ in the MnO₆ octahedra is observed at 1.2, 1.4, and 1.6 GPa, respectively, and it results in a reduction of the Jahn–Teller distortion commonly existing in the manganites. Effect of the unique 6s² long-pair character of the Bi³⁺ ion on the pressure dependence of the lattice distortion is discussed.     

Study on photoconductivity of dye-polymer-based solid-state thin film

In this article, we describe a solid-state photoelectrochemical cell for light detection. Safranine-T dye mixed with polyvinyl alcohol (PVA) solution was deposited on a conducting and transparent indium-tin-oxide (ITO)-coated glass that was used as one electrode and another ITO-coated glass as the counterelectrode. A solid polymeric electrolyte consisting of polyethylene oxide-ammonium perchlorate-ethylene carbonate and propylene carbonate with suitable weight ratio was prepared and sandwiched between these two ITO-coated glass electrodes, which were separated by a Teflon spacer about 50 μm thick. The cell was biased with a direct current source to make the dye and PVA-coated ITO as the anode and the other ITO as the cathode. On illumination by a tungsten lamp, from the cathode side, the change of photocurrent was measured. The dark current-voltage characteristics and the growth and decay of the photocurrent for steady and pulsed illumination were studied.     

稀土有机光→电、电→光转换器件

198 6年Ｔａｎｇ发表双层有机光伏电池[1] 与无机光伏电池相比 ,以重量轻 ,材料经济并可以沉积在柔性衬底上等潜在优势正在引起人们注意。目前对有机光伏效应的研究多集中在聚苯乙炔 (ＰＰＶ)及其衍生物上[2 ,3 ] ,能量转换效率在 10ｍＷ·ｃｍ- 2 紫外光照下可超过 4 % [4 ] ;以小分子有机物制成的光伏器件也得到研究人员的关注[5,6] 。但是采用稀土配合物作为电子给体层的有机光伏器件还未见报道。我们研究组一直对以稀土有机配合物为发光层的有机ＥＬ器件进行研究[7,8] 。在研究ＥＬ器件特性过程中 ,我们发现稀土有机电致发光器件在紫外…     

新型钴-聚吡咯-碳载Pt燃料电池催化剂的制备与表征

采用脉冲微波辅助化学还原法制备了钴-聚吡咯-碳（Co-PPy-C）载Pt 催化剂（Pt/Co-PPy-C）,其中Pt 的总质量占20%. 利用透射电镜（TEM）、光电子射线能谱分析（XPS）和X射线衍射（XRD）研究了催化剂的结构,用循环伏安（CV）、线性扫描伏安（LSV）等方法考察了其电化学活性及氧还原反应（ORR）动力学特性及耐久性. Pt/Co-PPy-C电催化剂的金属颗粒直径约1.8 nm,略小于商用催化剂Pt/C（JM）颗粒尺寸（约2.5 nm）;催化剂在载体上分散均匀,粒径分布范围较窄. Pt/Co-PPy-C的电化学活性比表面积（ECSA）（75.1 m²·g^-1）高于商用催化剂的ECSA（51.3 m²·g^-1）. XPS测试表明,自制催化剂表面的Pt 主要以零价形式存在. 而XRD结果显示,自制催化剂中Pt（111）峰最强,Pt 主要为面心立方晶格. Pt/Co-PPy-C具有与Pt/C（JM）相同的半波电位;在0.9 V下,Pt/Co-PPy-C的比活性（1.21 mA·cm^-2）高于商用催化剂的比活性（1.04 mA·cm^-2）,表现出更好的ORR催化活性.动力学性能测试表明催化剂的ORR反应以四电子路线进行. CV测试1000 圈后,Pt/Co-PPy-C和Pt/C（JM）的ECSA 分别衰减了13.0%和24.0%,可见自制催化剂的耐久性高于商用Pt/C（JM）,在质子交换膜燃料电池（PEMFC）领域有一定的应用前景.     

牛天然纤溶酶原Kringles结构域片段的获得及其抑制内皮细胞增殖作用研究

利用猪胰弹性蛋白酶和尿激酶限制性酶切牛纤溶酶原,获得了纤溶酶原Kringles结构域片段Kringles1-3(K1-3)和Kingles1-4(K1-4),研究发现,在没有自由巯基供体存在的条件下,尿激酶酶发牛纤溶酶原也能够产生K1－4,从而认为存在由尿激酶酶切牛纤溶酶原直接产生K1－4的途径,所获得的K1－3和K1－4对恒河猴脉络膜－视网膜RF／6A血管内皮细胞的增殖有抑制活性。