在材料科学领域，控制聚合物的结构形态以达到某种预设的性质或特征，一直是一个重要的研究目标。 一支来自美国GIT（the California Institute of Technology）的，由Robert H. Grubbs教授领衔的研究团队，挑战了这一难题，成功合成了一种大环有机纳米结构。论文在线发表在2011年5月的 Angew. Chem. Int. Ed. 期刊上（2009年IF=11.848）。 他们从各种各样的大单体（macromonomers）出发，利用一种能够促进环扩张转位聚合（ring expansion metathesis polymerization，REMP）的钌基催化剂（如下图），制备出了超高分子量的环形刷子聚合物（cyclic brush polymers，CBPs）。产物用静态LS及GPC-LS作了表征，同时用AFM技术进行了成像测定，表明直径大约有100-180 nm大小。 Reference : Synthesis and Direct Imaging of Ultrahigh Molecular Weight Cyclic Brush Polymers , Yan Xia, Andrew J. Boydston, Robert H. Grubbs, Angew. Chem. Int. Ed. 2011 . DOI: 10.1002/anie.201101860
Journal of Power Sources Article in Press, Accepted Manuscript - Note to users doi:10.1016/j.jpowsour.2011.03.004 | How to Cite or Link Using DOI Copyright 2011 Published by Elsevier B.V. Permissions Reprints High Performance Polymer Chemical Hydrogel-based Electrode Binder Materials for Direct Borohydride Fuel Cells Nurul A. Choudhury a , Jia Ma a , Yogeshwar Sahai , a , and Rudolph G. Buchheit a a Department of Materials Science and Engineering, The Ohio State University, 2041 College Road. Columbus, OH 43210, USA Received 30 December 2010; revised 2 March 2011; accepted 2 March 2011. Available online 10 March 2011. Abstract Novel, cost-effective, high-performance, and environment-friendly electrode binders, comprising polyvinyl alcohol chemical hydrogel (PCH) and chitosan chemical hydrogel (CCH), are reported for direct borohydride fuel cells (DBFCs). PCH and CCH binders-based electrodes have been fabricated using a novel, simple, cost-effective, time-effective, and environmentally benign technique. Morphologies and electrochemical performance in DBFCs of the chemical hydrogel binder-based electrodes have been compared with those of Nafion binder-based electrodes. Relationships between the performance of binders in DBFCs with structural features of the polymers and the polymer-based chemical hydrogels are discussed. The CCH binder exhibited better performance than a Nafion binder whereas the PCH binder exhibited comparable performance to Nafion in DBFCs operating at elevated cell temperatures. The better performance of CCH binder at higher operating cell temperatures has been ascribed to the hydrophilic nature and water retention characteristics of chitosan. DBFCs employing CCH binder-based electrodes and a Nafion-117 membrane as an electrolyte exhibited a maximum peak power density of about 589 mW cm−2 at 70°C. Keywords: Polyvinyl alcohol chemical hydrogel; Chitosan chemical hydrogel; Glutaraldehyde; Nafion; Electrode binder; Direct borohydride fuel cell
Journal of Power Sources Article in Press, Accepted Manuscript - Note to users doi:10.1016/j.jpowsour.2011.01.099 | How to Cite or Link Using DOI Copyright 2011 Published by Elsevier B.V. Permissions Reprints Controlling gas diffusion layer oxidation by homogeneous hydrophobic coating for polymer electrolyte fuel cells Yusuke Hiramitsu , a , , Hitoshi Sato a , , Kenji Kobayashi a , and Michio Hori a , a Fuel Cell Research Center, Daido University, 10-3 Takiharu-cho, Minami-ku, Nagoya 457-8530, Japan Received 21 June 2010; revised 10 January 2011; accepted 31 January 2011. Available online 17 February 2011. Abstract Reduced production costs and enhanced durability are necessary for practical application of polymer electrolyte fuel cells. There has been a great deal of concern about degradation of the gas diffusion layer located outside the membrane electrode assembly. However, very few studies have been carried out on the degradation process, and no suitable methods for improving the durability of the cell have been found. In this work, the influence on the cell performance and factors involved in the degradation of the gas diffusion layer has been clarified through power generation tests. Long-term power generation tests on single cells for 6000h were carried out under high humidity conditions with homogeneous and inhomogeneous hydrophobic coating gas diffusion layers. The results showed that the increase in the diffusion overvoltage from the gas diffusion layer could be controlled by the use of a homogeneous coating. Post analyses indicated that this occurred by controlling oxidation of the carbon fiber. Keywords: Polymer electrolyte fuel cell (PEFC); Water management; Water flooding; Gas diffusion layer (GDL); Durability; Long-term performance
Journal of Power Sources Article in Press, Accepted Manuscript - Note to users doi:10.1016/j.jpowsour.2011.02.028 | How to Cite or Link Using DOI Copyright 2011 Published by Elsevier B.V. Permissions Reprints A comparative study of Pt/C cathodes in Sn0.9In0.1P2O7 and H3PO4 ionomers for high-temperature PEMFCs Y.C. Jin a , M. Okada a and T. Hibino , a , a Graduate School of Environmental Studies, Nagoya University, Nagoya, Aichi 464-8601, Japan Received 20 December 2010; revised 24 January 2011; accepted 7 February 2011. Available online 16 February 2011. Abstract New Pt/C cathodes with many reaction sites for the oxygen reduction reaction as well as high tolerance to Pt corrosion have been designed for high-temperature proton exchange membrane fuel cells (PEMFCs), wherein a composite mixture of Sn0.9In0.1P2O7 (SIPO) and sulfonated polystyrene-b-poly(ethylene/butylene)-b-polystyrene (sSEBS) functioned as an ionomer. The microstructure of the Pt-SIPO-sSEBS/C cathode was characterized by homogeneous distribution of the ionomer over the catalyst layer and close contact between the ionomer and the Pt/C powder. As a result, the activation and concentration overpotentials of the Pt-SIPO-sSEBS/C cathode between 100 and 200°C were lower than those of an H3PO4-impregnated Pt/C cathode, which suggests that the present ionomer can avoid poisoning of Pt by phosphate anions and the limitation of gas diffusion through the catalyst layer. Moreover, agglomeration of Pt in the Pt-SIPO-sSEBS/C cathode was not observed during a durability test at 150°C for 6days, although it was significant in the Pt-H3PO4/C cathode. Therefore, it is concluded that the Pt-SIPO-sSEBS/C electrode is a very promising cathode candidate for high-temperature PEMFCs. Keywords: Cathode; High-temperature operation; Sn0.9In0.1P2O7; Sulfonated polystyrene-b-poly(ethylene/butylene)-b-polystyrene
Journal of Power Sources Article in Press, Accepted Manuscript - Note to users doi:10.1016/j.jpowsour.2011.01.086 | How to Cite or Link Using DOI Copyright 2011 Published by Elsevier B.V. Permissions Reprints In-Situ Metal Ion Contamination and the Effects on PEM Fuel Cell Performance Mark Sulek , a , , Jim Adams a , Steve Kaberline a , Mark Ricketts a and James R. Waldecker a a Ford Motor Company, Research and Advanced Engineering, 2101 Village Road, Dearborn, MI 48121 Received 3 December 2010; revised 21 January 2011; accepted 27 January 2011. Available online 2 February 2011. Abstract Automotive fuel cell technology has made considerable progress, and hydrogen fuel cell vehicles are regarded as a possible long-term solution to reduce carbon dioxide emissions, reduce fossil fuel dependency and increase energy efficiency. Even though great strides have been made, durability is still an issue. One key challenge is controlling MEA contamination. Metal ion contamination within the membrane and the effects on fuel cell performance were investigated. Given the possible benefits of using stainless steel or aluminum for balance-of-plant components or bipolar plates, cations of Al, Fe, Ni and Cr were studied. Membranes were immersed in metal sulfide solutions of varying concentration and then assembled into fuel cell MEAs tested in-situ. The ranking of the four transition metals tested in terms of the greatest reduction in fuel cell performance was: Al3+ Fe2+Ni2+, Cr3+. For iron-contaminated membranes, no change in cell performance was detected until the membrane conductivity loss was greater than approximately 15%. Keywords: PEM fuel cells; metal contamination; membrane degradation; metal ions; membrane contamination
高分子聚合物的动力学 侯吉旋 Introduction What is the soft condensed matter? F = U - TS 体系的自由能分为两部分， U 和 S 。 U 起主要贡献的体系，就是传统意义上的硬物质，而熵起主导作用的体系就是我们所说的软物质。 从自由能公式里就可以看得出，软物质对于温度 T 非常敏感。 对于钢铁做的弹簧，要拉开一定距离需要一定的力 F ，当我们把弹簧放在火上烤一烤，要拉开同样距离的话， F 几乎不怎么变化。但是如果把弹簧换成橡胶，那就完全不一样了，因为橡胶属于软物质。 高分子聚合物能带来什么有趣的事？ Non-Newtonian fluids elastic recoil 怎样研究高分子聚合物？ 物理学家研究一个体系，无非就是给体系一个变化，看体系的反应。 例如压一压物体，看物体形变了多少；在物体两端加个电压，看物体内部产生多大电流；给物体加热一些，看看物体需要吸收多大的能量，等等。 研究高分子熔体也是一样，加上一个瞬间剪切，看切应力是如何变化的。 stress relaxation modulus G ( t ) G ( t ) can also be determined by applying a constant strain, g s and observing stress relaxation over time: G ( t )= s (t)/ g s 研究高分子聚合物难在哪里？ 由于链与链之间不能相互穿透，这就行成了一种拓扑约束。数学上，对拓扑约束的描述是非常复杂的。 Reptation Theory 所幸的是，大约四十年前，Reptation理论诞生了，这个理论也促使法国科学家de Gennes获得了诺贝尔物理学奖。 Rouse Model-- 单链 Reptation-- 多链 然而Rouse理论和Reptation理论并不能完全解释高分子熔体中所有现象。当高分子链很短的时候可以用Rouse理论来解释，当高分子链及其长的时候可以用Reptation理论来解释。 然而处于中间的一大部分的区域无法得到很好的解释。 这个时候我们不能仅仅考虑Reptation这一个机理，还需要考虑另外两个很很重要的机理长度涨落(CLF)和限制脱落(CR)。 为了检验现有的一些管子理论，我们做了大量的计算机模拟。 我们发现现有的管子理论都不能给出完全符合计算机模拟数据的结果 。 n We present an extensive set of simulation results for the stress relaxation in bead-spring polymer melts. n We have performed parameter-free tests of several different tube models. Whats wrong with our theories???? 当所有的管子理论都不能给出完美的结果的时候，我们开始对其中的某一理论进行修正。 A possible explanation is a double-counting of the effect of short- wavelength (p Z) modes in Likhtman and McLeishs theory. we have removed from the CLF part of (t) the contribution of modes with a relaxation time shorter than entanglement time. n 注： 本博文中部分图片来自网络。 We repaired LM theory so that it shows excellent agreement with simulation data!
标签: 聚合物
