MEA with double-layered catalyst cathode to mitigate methanol crossover in DMFC

Methanol permeation is one of the key problems for direct methanol fuel cell (DMFC) applications. It is necessary to change the structure of the cathode of membrane electrode assembly (MEA). Therefore, a novel MEA with double-layered catalyst cathode was prepared in this paper. The double-layered catalyst consists of PtRu black as inner catalyst layer and Pt black as outer catalyst layer. The inner catalyst layer is prepared for oxidation of the methanol permeated from anode. The results indicate that this double-layered catalyst reduced the effects of methanol crossover and assimilated mixed potential losses. The performance of MEA with double-layered catalyst cathode was 52.2 mW cm⁻², which was a remarkable improvement compared with the performance of MEA with traditional cathode. The key factor responsible for the improved performance is the optimization of the electrode structure.     

Influence of the anode material on the characteristics of an analytical glow discharge cell

The energy transfer to the discharge gas due to various collision processes in the plasma and the heating of the sample are widely known effects in glow discharge (GD) spectroscopy. Despite of the considerable thermal effects and their serious influence on the performance of GD devices, measurements of the discharge gas and sample temperatures are not common at all. The gas temperature depends on the power absorption of the discharge as well as on the temperature of boundaries (sample and anode). In this work the influence of different anode materials in a Grimm-type source on the voltage–current characteristics, crater shapes and GD spectra is investigated. Anodes made of titanium and copper alloys, graphite, and steel with thermal conductivities covering a wide range of values are used. For a fixed voltage and pressure a decrease of the measured current is observed for bad thermal conductive anodes. Cooling of the sample results in an increase of the measured current. Both observations can be explained by changes of the discharge gas temperature. The temperature of the sample is measured from the back side and compared for different anodes. Further, it is found that the choice of the anode material (i) has no significant influence on the crater shape, (ii) results in slightly different sputtering rates and (iii) strong differences of the GD spectra.     

NiCo_2O_4对H_2O_2在碱性溶液中电化学还原反应的催化行为(英文)

利用溶胶-凝胶法合成纳米NiCo2O4,并利用X射线衍射和透射电镜分析其结构和表面形貌.结果表明NiCo2O4具有尖晶石结构,平均粒径约为15 nm.利用电势线性扫描和恒电势法测定了其对H2O2在碱性溶液中电化学还原反应的催化性能.发现NiCo2O4对H2O2电化学还原具有高的催化活性和稳定性,在H2O2浓度低于0.6 mol.L-1时,其电化学还原反应主要通过直接还原途径进行.以NiCo2O4为阴极催化剂的Al-H2O2半燃料电池在室温下的开路电压达1.6 V;在1.0 mol.L-1 H2O2溶液中,峰值功率密度达209 mW.cm-2,此时电流密度为220mA.cm-2.     

基于蓝黄磷光二元互补色的高效聚合物白光器件

研究了基于互补色的高效聚合物白光器件,双色材料包括蓝绿光材料双(4,6-二氟苯基吡啶-N,C2)吡啶甲酰合铱(Firpic)和黄光材料三[3-(2,6-二甲基苯氧基)-6-(2-噻吩基)-哒嗪]铱(Fs-1),器件结构为ITO/PEDOT(40 nm)/PVK:OXD-7:Firpic:Fs-1(80 nm)/Ba(4 nm)/Al(120 nm).当发光层材料PVK∶OXD-7∶Firpic∶Fs-1质量比为63∶27∶10∶0.25时,用溶液加工方法得到高效白光器件,此时CIE色坐标为(0.30,0.39),最大电流效率为10.8 cd.A-1,亮度可达到4200 cd.m-2.在此基础上,引入水溶性电子注入材料聚[9,9-二(3′-N,N-二甲基胺基丙基-2,7-芴-2,7-交-(9,9-二辛基芴)](PFN)修饰阴极界面,使载流子注入和传输更平衡,当阴极为PFN(20 nm)/Al(120 nm)时,电流效率获得显著改善,达到13.1 cd.A-1,此时电流密度为4.9 mA.cm-2,亮度可达到6096 cd.m-2,白光器件的色坐标为(0.33,0.39),同时发光光谱稳定.另外通过电致发光(EL)、光致发光(PL)光谱及能级结构图分析了载流子俘获和能量转移在发光中的作用.     

草酸盐共沉淀法制备锂离子电池正极材料LiNi0.5Mn0.5O2及其电化学性能

使用草酸盐共沉淀法合成了LiNi0.5Mn0.5O2, 并研究了共沉淀时的pH条件对终产物的结构、形貌及电化学性能的影响. 采用X射线衍射(XRD)和扫描电镜(SEM)表征了在pH值为4.0、5.5、7.0和8.5时得到的共沉淀和终产物LiNi0.5Mn0.5O2的结构和形貌. 使用充放电实验研究了不同pH条件下得到的LiNi0.5Mn0.5O2的电化学性能. 结果表明, pH为7.0时, 合成的材料颗粒更小、分布最均匀, 材料具有良好的层状特征, 且材料中锂镍的混排程度最小. 电化学测试结果印证了pH为7.0时合成的材料具有更好的电化学性能, 在0.1C的倍率下, 材料的首次放电比容量达到了185 mAh·g-1, 在循环20周后, 放电比容量仍然保持在160 mAh·g-1. X射线光电子能谱(XPS)测试结果表明, pH为7.0时合成的LiNi0.5Mn0.5O2中Ni为+2价, Mn为+4价.     

Short-living absorption and emission of CsI(Na)

This paper investigates the short-living absorption and the emission of CsI(Na) under a pulsed electron beam (Е_e=0.25 MeV, t_1/2=15 ns and W=0.003…0.16 J/cm²). The bands of singlet self-trapped excitons, as well as Na⁰ and V_k color centers have been detected in the transient absorption spectrum of CsI(Na). It has been found that the activator luminescence spectrum, peaking at 3.0 eV, fits a Gaussian (E_m=3.0 eV and FWHM=0.44±0.02 eV at 80 K) and remains the same at different time delays within 10⁻⁸-10⁻³ s. The decay kinetics of the 3.0 eV emission has one nanosecond exponential component and two microsecond ones with time constants 1.0 and 3.0 μs, which remain unchanged within 78-150 K. It is concluded that the activator emission is due to the radiative annihilation of sodium-perturbed two halide excitons from the non-relaxed singlet state. The pathways of such excitons creation are discussed.     

Fabrication of solid oxide fuel cell based on doped ceria electrolyte by one-step sintering at 800 °C

Ce_0.8Gd_0.05Y_0.15O_1.9 (GYDC) electrolyte was prepared by a carbonate co-precipitation method. Lithium nitrate at 1, 1.5, 2 and 3 mol% was added to GYDC as sintering additive. 96% relative density was achieved for GYDC at sintering temperature of 800 °C with addition of 1.5 mol% LiNO₃. The conductivities of GYDC with sintering aids LiNO₃ were measured by a.c. impedance spectroscopy and showed comparable values to that of pure GYDC sample sintered at 1400 °C. A single cell with 1.5 mol% LiNO₃ infiltrated GYDC electrolyte was fabricated by sintering at 800 °C for only 2 h. Lithiated NiO was synthesized by the glycine-nitrate combustion method and employed as cathode material. The cell was tested at temperatures from 500 to 575 °C and a maximum power density of 73 mW cm^− 2 was obtained at 575 °C. These preliminary results indicate that LiNO₃ is a very effective sintering additive for intermediate temperature solid oxide fuel cell fabrication.     

Li-ion migration in Li2FeSiO4-related cathode materials: A DFT study

The orthosilicate family of materials Li₂MSiO₄ for M = Fe, Mn and Co are coming to be seen as potentially cheap cathode materials for large-scale Li-ion batteries, not least through the possibility for significant capacity gains if more than one Li-ion can be removed per formula unit. To gain insights into possible Li-ion migration pathways and diffusion barriers for Li-ions, model systems for Li_xFeSiO₄ (x ≈ 1, 2) are here studied using the Density Functional Theory (DFT) approach. Li-ion and ion-vacancy migration barriers are calculated for a number of model systems. The results help explain why the Li/Fe site-mixing observed during electrochemical cycling of Li₂FeSiO₄ does not lead to any noticeable loss in cell performance, despite the increased tortuosity introduced into the Li-migration pathways by this ion-mixing process.     

Reduction of 1,2-dicarbonyl compounds and of their N-phenylimine derivatives by sodium cyanide under aprotic conditions

Some aromatic 1,2-dicarbonyl compounds, i.e. 9,10-phenanthrenequinone, acenaphthenequinone and benzil, and their corresponding N-phenyl monoimines, have been reduced, using dry acetonitrile as the solvent, in the presence of sodium cyanide as a reducing agent. Comparative potentiostatic preparative-scale electrolysis is described.     

热解二氧化钛/聚苯胺制备高效非贵金属氧还原电催化剂

为了克服传统Pt系催化剂价格昂贵、稳定性差的缺点,采用热解新型Ti O2/聚苯胺(PANI)复合物的方法合成了Ti O2/C催化剂.用扫描电子显微镜、X射线光电子能谱、X射线衍射、傅里叶变换红外光谱、拉曼光谱、透射电子显微镜、循环伏安法和线性扫描伏安法等方法研究了热处理和PANI复合比例对复合物的形貌、成键、晶相组成及氧还原性能的影响.结果表明,PANI与Ti O2间存在相互作用,可以抑制Ti O2的团聚和锐钛矿向金红石的转变.热处理制得Ti O2/C的氧还原活性随着PANI载体含量增加先升高后降低,PANI和Ti O2质量比为35/100时,催化剂的氧还原活性最高.同时,循环伏安和时间-电流曲线测试表明,已制备的复合材料在催化氧还原反应进行时具有较好的稳定性.