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151.
Significant progress has been made in the last few years toward synthesizing highly dispersible inorganic catalysts for application in the electrodes of direct methanol fuel cells. In addition, research toward achieving an efficient catalyst supporting matrix has also attracted much attention in recent years. Carbon black- (Vulcan XC-72) supported Platinum and Platinum-Ruthenium catalysts have for long served as the conventional choice as the cathode and the anode catalyst materials, respectively. Oxygen reduction reaction at the cathode and methanol oxidation reaction at the anode occur simultaneously during the operation of a direct methanol fuel cell. However, inefficiencies in these reactions result in a generation of mixed potential. This, in turn, gives rise to reduced cell voltage, increased oxygen stoichiometric ratio, and generation of additional water that is responsible for water flooding in the cathode chamber. In addition, the lack of long-term stability of Pt-Ru anode catalyst, coupled with the tendency of Ru to cross through the polymer electrolyte membrane and eventually get deposited on the cathode, is also a serious drawback. Another source of potential concern is the fact that the natural resource of Pt and the rare earth metal Ru is very limited, and has been predicted to become exhausted very soon. To overcome these problems, new catalyst systems with high methanol tolerance and higher catalytic activity than Pt need to be developed. In addition, the catalyst-supporting matrix is also witnessing a change from traditionally used carbon powder to transition metal carbides and other high-performance materials. This article surveys the recent literature based on the advancements made in the field of highly dispersible inorganic catalysts for application in direct methanol fuel cells, as well as the progress made in the area of catalyst-supporting matrices. 相似文献
152.
Residual symmetry reductions and interaction solutions of the (2+1)-dimensional Burgers equation 下载免费PDF全文
In nonlinear physics,it is very difficult to study interactions among different types of nonlinear waves.In this paper,the nonlocal symmetry related to the truncated Painleve′expansion of the(2+1)-dimensional Burgers equation is localized after introducing multiple new variables to extend the original equation into a new system.Then the corresponding group invariant solutions are found,from which interaction solutions among different types of nonlinear waves can be found.Furthermore,the Burgers equation is also studied by using the generalized tanh expansion method and a new Ba¨cklund transformation(BT)is obtained.From this BT,novel interactive solutions among different nonlinear excitations are found. 相似文献
153.
《Current Applied Physics》2015,15(9):993-999
Pt-transition metal alloy catalysts with an active Pt surface have exceptional properties for use in oxygen electro-reduction reactions in fuel cells. Herein, we report the simple synthesis of dealloyed PtCu catalysts and their catalytic performance in oxygen reduction. The dealloyed PtCu catalysts consisted of a Pt-enriched shell with a Pt–Cu alloy core and were synthesized through a chemical co-reduction process followed by thermal annealing and chemical dealloying. During synthesis, thermal annealing leads to a high degree of formation of PtCu alloy particles (e.g., PtCu or PtCu3), and chemical dealloying causes selective dissolution of unstable Cu species from the surface layers of the PtCu alloy particles, resulting in a PtCu alloy@Pt-enriched surface core–shell configuration. Our PtCu3/C catalyst exhibits a great improvement in the oxygen reduction reaction with a mass activity of 0.501 A/mgPt, which is 2.24 times greater than that of a commercial Pt catalyst. In this article, the synthesis details, characteristics and performance improvements in ORR of chemically dealloyed PtCu catalysts are systemically explained. 相似文献
154.
采用锌-柠檬酸氢二铵溶液还原体系,以偶氮苯为原料合成出氢化偶氮苯.合成反应的最佳反应条件:当偶氮苯用量是0.625 mmol时,偶氮苯与锌的物质的量之比为1:5,0.2 g/mL柠檬酸氢二铵溶液用量5.0 mL,室温,时间约3 min,平均收率90.63%. 相似文献
155.
Development of Graphene/CdSe Quantum Dots‐Co Phthalocyanine Nanocomposite for Oxygen Reduction Reaction 下载免费PDF全文
Nanocomposites containing CdSe quantum dots, tetra(4‐(4,6‐diaminopyrimidin‐2‐ylthio) phthalocyaninatocobalt(II)) (CoPyPc) and reduced graphene nanosheets (rGNS) were devoloped and used for the modification of a glassy carbon electrode. Characterization of the nanocomposites was done by transmission electron microscopy (TEM) and X‐ray diffraction (XRD) analyses. Cyclic voltammetry (CV) was used for electrochemical characterization of the prepared nanocomposite for oxygen reduction reaction. The oxygen reduction activity for rGNS/CdSe‐CoPyPc nanocomposite was found to be superior over the individual nanomaterials in this study. The activity of the nanocomposite towards oxygen reduction was also tested for tolerance to methanol crossover effect using chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS) studies. 相似文献
156.
Jens Mohr Prof. Dr. Martin Oestreich 《Angewandte Chemie (International ed. in English)》2014,53(48):13278-13281
The hydrogenation of oximes and oxime ethers is usually hampered by N? O bond cleavage, hence affording amines rather than hydroxylamines. The boron Lewis acid B(C6F5)3 is found to catalyze the chemoselective hydrogenation of oxime ethers at elevated or even room temperature under 100 bar dihydrogen pressure. The use of the triisopropylsilyl group as a protecting group allows for facile liberation of the free hydroxylamines. 相似文献
157.
At polymer-solid contacts with thermoplastic polymers, the chain characteristics can deviate from the bulk on a length-scale of several nanometer in the so-called interphase. Such an interphase depends on the interaction between respective macromolecule and substrate, and affects the free volume in the polymer. Here, we review our experiments on the characterization of the free volume by positron lifetime spectroscopy at planar and curved interfaces. For Teflon AF on silicon, we identify a layer of increased density, corresponding to an interphase width of some 10 nm. PEP based nanocomposites with functionalized silica show no interphase, whereas for functionalized POSS an interphase is detected. 相似文献
158.
《中国化学》2014,(1):44-50
A novel biomaterial based on polyurethane (PU) was prepared through physical incorporation of lysine-containing copolymer to improve its hemocompatibility and surface recognition of plasminogen.The lysine-containing copolymer was synthesized via the copolymerization of 2-ethylhexyl methacrylate (EHMA),oligo (ethylene glycol)methyl ether methacrylate (OEGMA) and 6-tert-butoxycarbonyl amino-2-(2-methyl-acryloylamino)-hexanoic acid tert-butyl ester (Lys(P)MA),followed by the deprotection of COOH and ε-NH2 groups on lysine residues in the copolymer.The composition of the copolymer can be adjusted by varying the monomer feed ratio.The three components contribute to improving the compatibility with PU,resistance to nonspecific protein adsorption and specific binding of plasminogen,respectively.The binding capacity towards plasminogen increased with the lysine content in the copolymer.This approach illustrates a simple way for the generation of novel biomaterials with improved hemocompatibility and surface recognition of specific biomolecules. 相似文献
159.
160.
We first review the Coset Space Dimensional Reduction (CSDR) programme and present the best model constructed so far based on the , 10‐dimensional E8 gauge theory reduced over the nearly‐Kähler manifold with the additional use of the Wilson flux mechanism. Then we present the corresponding programme in the case that the extra dimensions are considered to be fuzzy coset spaces and the best model that has been constructed in this framework too. In both cases the best model appears to be the trinification GUT . 相似文献