Pt nanocrystals electrodeposited on reduced graphene oxide/carbon fiber paper with efficient electrocatalytic properties

Carbon fiber paper(CFP) wrapped with reduced graphene oxide(rGO) film as the composite support(rGO/CFP) of Pt catalysts was studied. It was found that rGO could affect the size and morphology of Pt nanocrystals(NCs). Concave nanocubes(CNC) Pt NCs~ 20 nm were uniformly electrodeposited on high reduced HrGO/CFP while irregular Pt NCs~62 nm were loaded on low reduced LrGO. Compared with Pt-LrGO/CFP and Pt-MrGO/CFP, the CNC Pt-HrGO/CFP exhibited a higher electrochemically active surface area(121.7 m~2 g~(-1)), as well as enhanced electrooxidation activity of methanol(499 mA mg~(-1)) and formic acid(950 mA mg~(-1)). The results further demonstrated that the CNC Pt-HrGO/CFP could serve as the gas diffusion electrode in fuel cells and yielded a satisfactory performance(1855 mW mg~(-1)). The work can provide an attractive perspective on the convenient preparation of the novel gas diffusion electrode for proton exchange membrane fuel cells.     

Wet spinning of PVA composite fibers with a large fraction of multi-walled carbon nanotubes

PVA composites fibers with a large fraction of multi-walled carbon nanotubes modified by both covalent and non-covalent functionalization were produced by a wet-spinning process.Model XQ-1 tensile tester,thermogravimetric analysis,scanning electron microscopy,differential scanning calorimetry,and wide-angle X-ray diffraction were used to characterize the properties of PVA/MWNT composite fibers.The TGA results suggested that MWNTs content in composite fibers were ranged from 5.3 wt%to 27.6 wt%.The mechanical properties of PVA/MWNT composite fibers were obviously superior to pure PVA fiber.The Young's modulus of composite fibers enhanced with increasing the content of MWNTs,and it rised gradually from 6.7 GPa for the pure PVA fiber to 12.8 GPa for the composite fibers with 27.6 wt%MWNTs.Meanwhile,the tensile strength increased gradually from 0.39 GPa for the pure PVA fiber to 0.74 GPa for the composite fibers with 14.4 wt%MWNTs.Nevertheless,the tensile strength of the composite fibers decreased as the MWNTs content up to 27.6 wt%.SEM results indicated that the MWNTs homogeneously dispersed in the composite fibers,however some agglomerates also existed when the content of MWNTs reached27.6 wt%.DSC results proved strong interfacial interaction between MWNTs and PVA chain,which benefited composite fibers in the efficient stress-transfer.WXAD characterization showed that the orientation of PVA molecules declined from 94.1%to 90.9%with the increasing of MWNTs content.The good dispersibility of MWNTs throughout PVA matrix and efficient stress-transfer between MWNTs and PVA matrix may contributed to significant enhancement in the mechanical properties.     

Polyaniline nanostructures tuning with oxidants in interfacial polymerization system

Three kinds of nanostructured polyanilines (PANIs) were prepared through interfacial polymerization by using ammonium persulfate (APS) as a single oxidant, and APS/FeCl3, APS/K2Cr2O7 as composite oxidants, respectively. It is observed that faster formation process and higher yield of nanostructured PANIs could be achieved in the presence of FeCl3 and K2Cr2O7. The as-prepared PANIs were characterized by field emission scanning electron microscopy, ultraviolet–visible absorption spectroscopy, Fourier transform infrared and Raman spectroscopy, X-ray diffraction analysis and electrochemical measurements including cyclic voltammetry and galvanostatic charge/discharge measurement. The influence of composite oxidants on the morphology, microstructure, and electrical and electrochemical properties of PANIs was discussed. Interestingly, when APS/K2Cr2O7 was used as the composite oxidants, PANI exhibited petal-like structure with high yield of 57.35% instead of general nanofibrous morphology formed in interfacial polymerization. Compared with those nanofibrous PANIs obtained by using APS as a single oxidant or APS/FeCl3 as composite oxidants, petal-like PANIs exhibited the largest specific capacitance (692.4 F/g at scan rate of 5 mV/s) and highest cycle stability among them. It provides a new insight into the control of PANI nanostructures with high yield and energy storage ability by simply selecting suitable composite oxidants in interfacial polymerization.     

CuO-海泡石/PMMA-PEG复合凝胶聚合物电解质的制备与性能

通过沉淀法合成了CuO-海泡石,再经溶液浇注法得到不同含量CuO-海泡石掺杂的PMMA-PEG基复合凝胶电解质膜。采用扫描电镜观察、X射线衍射分析、红外光谱、热重和电化学阻抗手段对复合凝胶电解质膜的结构和电化学性能进行了测试。结果表明,复合聚合物膜表面呈多孔状,且CuO-海泡石在复合聚合物膜中实现了良好分散。随着CuO-海泡石含量增加,复合凝胶电解质膜的电导率增高,热稳定性也明显提高。     

复合材料双语教学的研究与初探

复合材料是材料学专业的一门专业教学课程,采用双语教学学习复合材料并进一步对国内外的研究进展有更深入的认识。随着大学对专业课的扩展内容要求,复合材料课程内容与相关国外的进展知识要有更深入的了解,通过对双语教学的学习,能够从多方面对复合材料的专业知识、以及对专业词汇的学习有较大的提高。     

采用综掘技术实现煤巷快速掘进

阐述了我国高产高效矿井建设过程中，广泛应用锚杆支护，并在有条件的矿井使用掘锚机或连续采煤机，实现煤巷快速掘进。     

废除上证综指，启用沪深300指数提高决策水平的可行性分析

科学的政策需要以科学的工具来实现，本文在全面总结上证综指以及沪深300指数的优点和弊端的基础上，进行了废除上证综指的编制，全面启用沪深300指数来提高我国宏观经济管理部门的决策的科学性的可行性分析。得出了可供我国政府进一步提高股票市场监管水平的政策建议。     

Time series forecasts and extra-model information

Often a forecaster has supplementary information (e.g. field reports or forecasts from another source) that cannot be included directly in a time series model. Especially interesting are cases where this information is given at time intervals that are different from those of the time series model forecasts. Previous authors have considered a numerical and a model-based statistical method for combining extra-model information of this type with ARIMA model forecasts. This paper extends both methods to vector ARMA model forecasts and dynamic regression (transfer function) model forecasts. It is also shown that a Lagrange multiplier numerical procedure arises as a special case of the model-based procedure. An empirical example is given.     

受轴向均布载荷的压弯组合梁的计算

本文以受轴向、横向均布载荷且两端为固定饺支的组合梁为例,介绍如何用能量法来求解这类问题;讨论轴向均布载荷对弯矩放大系数的影响,并给出何时应考虑轴向压力对弯矩影响的近似判别式。