PEFC catalyst layers: Effect of support microstructure on both distributions of Pt and ionomer and cell performance and durability

In order to improve the performance and durability of polymer electrolyte fuel cells (PEFCs), various improvements in the microstructures of cathode catalyst layers (CLs) were initiated in the early 1990s. More recent advances in CL materials are highlighted, including carbon supports for improved accessibility of Pt nanoparticles (NPs), adsorption of ionomer on the Pt surface, high-oxygen-permeability ionomers, corrosion resistance of mesoporous and microporous carbons, and conductive ceramic supports with a fused-aggregate network structure. These approaches are summarized as stepwise improvements. The influences of the support structure on the distribution of Pt NPs and ionomer are reviewed, as well as their effects on performance and durability. These approaches for carbon supports are extended to conductive ceramic supports and the unique advantages are discussed.     

Nonlinear free vibrations of porous composite microplates incorporating various microstructural-dependent strain gradient tensors

The main objective of the present numerical analysis is to predict the nonlinear frequency ratios associated with the nonlinear free vibration response of porous composite plates at microscale in the presence of different microstructural gradient tensors. To achieve this end, by taking cubic-type elements into account, isogeometric models of porous composite microplates are obtained with and without a central cutout and relevant to various porosity patterns of distribution along the plate thickness. The established unconventional models have the capability to capture the effects of various unconventional gradient tensors continuity on the basis of a refined shear deformable plate formulation. For the simply supported microsized uniform porous functionally graded material (U-PFGM) plate having the oscillation amplitude equal to the plate thickness, it is revealed that the rotation gradient tensor causes to reduce the frequency ratio about 0.73%, the dilatation gradient tensor causes to reduce it about 1.93%, and the deviatoric stretch gradient tensor leads to a decrease of it about 5.19%. On the other hand, for the clamped microsized U-PFGM plate having the oscillation amplitude equal to the plate thickness, these percentages are equal to 0.62%, 1.64%, and 4.40%, respectively. Accordingly, it is found that by changing the boundary conditions from clamped to simply supported, the effect of microsize on the reduction of frequency ratio decreases a bit.

     

超分子构筑调控合成结构规整的梯形聚合物及其应用研究

综述了"超分子构筑调控的逐步偶联/聚合法",该方法将高分子化学与超分子化学相结合,利用多种类型的超分子弱键协同作用首先构筑预期的梯形超分子结构,再经聚合得到共价键梯形高分子.利用该方法合成了一系列结构规整的氧桥基和有机桥基梯形聚硅氧烷以及碳基梯形聚酯,并利用侧基间π-π叠加作用实现了对聚合物立体构型控制.扼要介绍了梯形聚合物在先进材料方面的应用,例如梯形聚硅氧烷液晶光致取向膜;由梯形聚硅氧烷合成的管状聚硅氧烷在高室温储存期微电子环氧塑封料方面的应用;以及基于梯形聚硅氧烷的拟筛板聚合物在二阶非线性光学材料方面的应用等.     

碳纳米纤维吸附储氢性能分析

文中综合碳纳米纤维微观结构的表征结果以及氢吸脱附等温线的实验测量结果,对碳纳米纤维的吸附储氢性能进行了综合分析,分析发现:比表面积和中孔容积均与氢吸附量成线性关系;微孔容积对材料吸附性能影响较大,微孔容积与氢吸附量成抛物线关系;氢在常温左右以及77K下的吸附等温线呈现超临界气体的吸附特征,氢在273K和353K下的吸脱附等温线也基本重合,呈现的是物理吸附的特征。实验结果还说明:常温左右,甚至是77K下,碳纳米纤维均不适合于氢的吸附储存。     

X7R型MLCC流延瓷膜显微结构的AFM研究

片式电容是由电介质陶瓷薄膜和内电极相互重叠而成的多层独石结构,又称多层陶瓷电容器(mul-tilayer ceram ic capacitors,简称MLCC)。具有体积小、内部电感低、绝缘电阻高及漏电流小、介质损耗低、价廉等优点,被广泛应用于各种电子整机中的振荡、耦合、滤波和旁路电路,尤其是高     

Microstructure evolution of room-temperature-sputtered ITO films suitable for silicon heterojunction solar cells

Thickness influence on structural, optical and electrical properties of sputtered indium tin oxide (ITO) with thickness ranging from 60 up to 430 nm films has been studied. At the increase of the film thickness crystallinity degree and grain size increased, whereas tensile structural distortion as well as resistivity decreased. It was observed that a microstructure evolution takes place: the initial amorphous layer evolved in polycrystalline phase, with a grain–subgrain surface morphology. Carrier concentration increased at the increase of the film thickness and a general relationship between electrical characteristics and structural distortion has been found. In thinner films larger tensile distortion allowed to include larger amount of interstitial O and/or Sn atoms in the lattice. An appreciable impact of the thickness was also observed on electro-optical properties in terms of changes in energy gap, resistivity and optical absorption. Silicon heterojunction solar cells have been produced and J_sc as high as 33.0 mA/cm² has been obtained.     

微波合成SrTiO3的工艺、结构与性能研究

应用微波会成这一材料合成新方法制备SrTiO3，研究了不同工艺条件下微波合成产物的结构，确定出制备纯净SrTiIO。的合成条件．对微波合成的工艺及其影响因素进行详细的探索，从合成产物的显微结构、粒度分布、比表面积、烧结性能等方面比较了微波合成与常规固相合成的差别，结果表明微波合成与各种常规方法相比有合成时间短、合成工艺简单、合成产物性能好等特点，是一种有发展潜力的材料合成技术．     

复合卤氧化铋纳米材料的合成及其光催化性能

采用低温沉淀法合成了一系列Bi OMxN1-x(M,N=Cl、Br、I)(0X1)复合材料,通过XRD、FESEM、TEM、EDS、UV-vis和PL等一系列表征和对有机物罗丹明光催化降解性能的研究表明:通过对复合材料合成过程中卤素离子含量的控制,使得此类固溶体具有独特的微观形貌和可控能带隙,使其在可见光下具有独特的光催化性能。在相同的光照条件下,Bi OCl0.5Br0.5、Bi OCl0.75I0.25和Bi OBr0.75I0.25相对于其他同系列的Bi OMxN1-x(M,N=Cl、Br、I)(0X1)微球样品而言,具有最好的光催化性能。     

氩离子激光固化环氧树脂制作三维微结构

利用激光束进行三维成像是通过逐层光引发聚合形成宏观尺度的三维实体 .最近出现的激光全息光刻技术是利用激光束的干涉产生三维全息图案 ,让感光树脂在全息图案中曝光 ,从而一次形成三维周期有序微结构 .通过调节激光干涉及波长可控制三维结构的形状及尺寸 .利用该技术获得亚微米尺度上周期性重复的三维微结构 ,可用于制作三维光子晶体 [1,2 ]等具有独特性能的聚合物材料 .本文用铁芳烃化合物与特种环氧树脂配制成阳离子型可见光固化树脂 ,在氩离子激光器产生的多束可见连续激光相干形成的空间干涉光场中曝光 ,成功地制备出亚微米量级的三…     

Development and application of high strength ternary boride base cermets

Reaction boronizing sintering is a novel strategy to form a ternary boride coexisting with a metal matrix in a cermet during liquid phase sintering. This new sintering technique has successfully developed world first ternary boride base cermets with excellent mechanical properties such as Mo₂FeB₂, Mo₂NiB₂ and WCoB base ones.In these cermets Mo₂FeB₂ and Mo₂NiB₂ base ones consist of a tetragonal M₃B₂ (M: metal)-type complex boride as a hard phase and a transition metal base matrix. The cermets have already been applied to wear resistant applications such as injection molding machine parts, can making tools, and hot copper extruding dies, etc.This paper focuses on the characteristics, effects of the additional elements on the mechanical properties and structure, and practical applications of the ternary boride base cermets.