纤维素中空纤维膜气体加湿性能的研究

采用纤维素N甲基吗啉N氧化物(NMMO)水三元纺丝体系,以去离子水为芯液,自来水为凝胶浴,湿法纺制了纤维素中空膜.经自然干燥后该膜的轴向、径向都明显收缩,断面呈现均质致密结构.干膜在水中会明显溶胀,重新润湿后具有气密性.考察了加湿水温、水气压力差等因素对膜的水渗透通量的影响,并初步测试了膜对质子交换膜燃料电池(PEMFC)反应气体H2和O2的加湿性能.实验结果表明该膜透水性能较优,气体加湿效果明显,具有应用于PEMFC反应气体加湿系统的潜力.     

Water uptake and infrared absorption in SrZr<Subscript>0.95</Subscript>M<Subscript>0.05</Subscript>O<Subscript>3-</Subscript><Subscript>a</Subscript> (<Emphasis Type="Italic">M</Emphasis>=Ga,Sc, Y and Nd)

Summary Proton concentration in SrZr_0.95M_0.05O_3-α (M=Ga, Sc, Y and Nd) was measured with a thermobalance at different temperatures (T=673-973 K) and water vapor pressures (P_H2O=0.9-12.8 kPa). At all the pressures and temperatures examined, the amount of proton concentration in these samples is in the order of Sc>Y>Ga>Nd. By an equilibrium evaluation, we estimated the maximum possible proton concentration about 2.0 mol% in these samples. Infrared (IR) absorption spectra are measured in these samples. The absorption bands can be fitted by four (M=Ga, Y, Nd) or three (M=Sc) Gaussian bands.     

Preparation and hydrogen permeation of BaCe0.95Nd0.05O3−δ membranes

A mixed proton–electron conducting perovskite made of BaCe_0.95Nd_0.05O_3−δ (BCN) was prepared by EDTA/citric acid complexing method. The precursor was characterized by differential scanning calorimetry (DSC), thermogravimetry (TG), and X-ray diffraction (XRD). In order to learn the perovskite formation process during the calcination, the intermediate, i.e. the sample calcined at 750 °C for 5 h, was investigated by scanning (STEM), energy-filtered (EFTEM), and high-resolution transmission electron microscopy (HRTEM) as well as electron energy-loss spectroscopy (EELS). The results revealed that the perovskite structure was formed via a solid-state reaction between barium–cerium mixed carbonate and cerium–neodymium mixed oxide particles. Dense mixed proton–electron conducting BCN membranes were made by pressing BCN powder followed by sintering. The microstructure of the sintered membranes was investigated by scanning electron microscopy (SEM). Hydrogen permeation through the BCN membrane was studied using a high-temperature permeator. The hydrogen permeation fluxes under wet conditions are higher than those under dry conditions, which is due to increased proton concentrations in the H⁺ hopping via OH groups. The hydrogen permeation increased with increasing hydrogen and steam concentrations in the feed. For a steam concentration of 15 vol.%, the hydrogen permeation flux reaches 0.026 ml/min cm².     

侧链型含氟磺化聚醚砜/磺化聚酰亚胺共混质子交换膜的制备及性能

制备了一类侧链型含氟磺化聚醚砜(s SPFES)与磺化聚酰亚胺(SPI)共混质子交换膜(s SPFES/SPI),研究了其吸水率、尺寸变化、质子电导率及稳定性等性能.结果表明,2种磺化聚合物以三乙胺盐型溶液共混及铸膜时相容性良好,制备的s SPFES/SPI共混质子交换膜结构均一,透明结实,离子交换容量为1.76~1.88 mmol/g.s SPFES/SPI共混质子交换膜表现出横向低于纵向的各向异性尺寸变化特性,在60℃水中横向尺寸变化率低于10%,经140℃加压水处理24 h后仍能保持较好的机械强度,质量损失低于6.1%.当温度高于50℃时,完全水合状态下的s SPFES/SPI共混质子交换膜的质子电导率均达到0.1 S/cm.     

Ab initio MD simulations of a prototype of methyl chloride hydrolysis with explicit consideration of three water molecules: a comparison of MD trajectories with the IRC path

Ab initio molecular dynamics simulations at the Hartree-Fock/6-31G level of theory are performed on methyl chloride hydrolysis with explicit consideration of one solute and two solvent water molecules at a temperature of 298 K. The reaction involves the formation of a reactant complex and the energy surface to the transition state is found to be simple. Two types of trajectories toward the product are observed. In the first type, the system reaches an intermediate complex (complex-P1) region after two nearly concerted proton transfers involving the attacking water molecule and the solvent water molecules. These trajectories resemble the intrinsic reaction coordinate trajectory. The thermal motion of the atoms leads the system to another intermediate complex (complex-P2) region. A second type of trajectory is found in which the system reaches the complex-P2 region directly after the proton transfers. In both of these forward trajectories, back proton transfers lead the system to a final complex-F region which resembles protonated methanol. Received: 3 July 1998 / Accepted: 2 September 1998 / Published online: 15 February 1999     

钨磷酸(钨硅酸)/聚乙烯醇复合物的制备和光、电性质研究

Kessin型的杂多酸及其盐是多酸化学中研究得最多的物种[1],近年来,以Keggin型的钨磷酸、钨硅酸为代表的多种杂多酸在固体和材料化学领域受到人们的关注[2],并在固体修饰电极、光（电）致变色材料、离子选择性电极和传感器等方面得到了广泛应用[3-5]．本文报道了Keggin型的钨磷酸、钨硅酸／聚乙烯醇复合物的合成、表征、光致变色性质及导电性．1实验方法技文献[6]方法制备H4[SiW12O40]·mH2O和H2［PW12O40］·nH对晶体,含水量用热重分析测得．将聚合度为1800士100的聚乙烯酸（PVA）0．5g溶于200mL沸水中,在65C,搅拌条件下分批…     

Secondary reduction strategy synthesis of Pt–Co nanoparticle catalysts towards boosting the activity of proton exchange membrane fuel cells

Based on the volcanic relationship between catalytic activity and key adsorption energies, Pt–Co alloy materials have been widely studied as cathode oxygen reduction reaction (ORR) catalysts in proton exchange membrane fuel cells (PEMFCs) due to their higher active surface area and adjustable D-band energy levels compared to Pt/C. However, how to balance the alloying degree and ORR performance of Pt–Co catalyst remains a great challenge. Herein, we first synthesized a well-dispersed Pt/Co/C precursor by using a mild dimethylamine borane (DMAB) as the reducing agent. The precursor was calcined at high temperature under H₂/Ar mixed gas by a secondary reduction strategy to obtain an ordered Pt₃Co intermetallic compound nanoparticle catalyst with a high degree of alloying. The optimization of electronic structure due to Pt–Co alloying and the strong metal-carrier interaction ensure the high kinetic activity of the cell membrane electrode. Additionally, the high degree of graphitization increases the electrical conductivity during the reaction. As a result, the activity and stability of the catalyst were significantly improved, with a half-wave potential as high as 0.87 V, which decreased by only 20 mV after 10000 potential cycles. Single-cell tests further validate the high intrinsic activity of the ordered Pt₃Co catalyst with mass activity up to 0.67 A mg_pt⁻¹, exceeding the United States Department of Energy (US DOE) standard (0.44 A mg_pt⁻¹), and a rated power of 5.93 W mg_pt⁻¹.     

带有对称垂直导体脊的平行板电容器内的电场及其电容量

利用保角变换法研究带有对称垂直导体脊的平行板电容器的电场,给出其电势分布和场强分布函数,通过MATLAB软件绘制电场线和等势线(面)图,并计算其电容量.     

Dual-band high impedance surface with graphene-based metasurfaces

High impedance surface (HIS) is an electromagnetic band gap (EBG) material that shows magnetic conductor surface properties within its band gap frequencies. The operation bandwidth is corresponding to the frequency range, where the reflection phase varies between +90^∘ and −90^∘. In this paper, a dual-band HIS is investigated based on planar periodic graphene arrays placed on a grounded dielectric substrate. Analytical circuit model of the graphene array together with the transmission line theory is employed to analyze the proposed structure. We demonstrate that the HIS bands can be adjusted by tuning the geometrical parameters of the structure and the Fermi level of graphene. The graphene-based HIS promises future applications in the low-profile, high gain and high efficiency antennas at THz frequencies.     

固体电解质质子导体的研究进展

介绍了固体电解质质子导体的应用、结构、质子传输机理以及国内外的最新研究进展,详细地综述了钙钛矿型和非钙钛矿型固体电解质质子导体的多种结构类型以及其质子传导机理的最新理论研究,同时分别介绍了两种质子导体的发展概况和面临问题,展望了未来质子导体的发展前景.