Effect of properties of active carbon supports on performance of Pt/C catalysts in polymer electrolyte membrane fuel cell

The Pt/C catalysts were prepared with pine active carbon and Vulcan XC-72 active carbon as the supports. The performances of the Pt/C catalysts in polymer electrolyte membrane fuel cell were compared. The result indicates that the performance of Pt/Vulcan XC-72 is better than that of Pt/pine. The physical and chemical properties of the two active carbons were measured using several analysis techniques. It was found that the pore size, specific conductivity and the surface function group significantly influence the performance of the electrocatalyst.

Poly(3-dodecylthiophenes) polymerized with different amounts of catalyst

The effect of the amount of the catalyst FeCl3, used during the direct oxidation polymerization, on the structure and properties of the obtained poly(3-dodecylthiophene) (P3DDT) was investigated in this paper. Such measurements as gel permeation chromatography (GPC), nuclear magnetic resonance (NMR) spectroscopy, thermal analysis, X-ray diffraction, infrared spectroscopy (FTIR) and ultraviolet-visible (W-vis) spectroscopy were applied. It is found that a suitable addition of FeCl3 can contribute to generate a P3DDT with greater percentage of head-to-tail head-to-tail (HT-HT) linkages, which are generally favored. The reduction of the other linkage defects helps to lengthen conjugation length, thus leading to more orderly chain packing. (C) 2000 Elsevier Science S.A. All rights reserved.

Chemiluminescent determination of luminol and hydrogen peroxide using hematin immobilized in the bulk of a carbon paste electrode

A new method for immobilization of a chemiluminescent reagent is presented. It is based on immobilizing hematin, a catalyst for luminol reaction, in the bulk of a carbon paste electrode. Bulk-immobilization allows renewal of the surface by simple polishing or cutting to expose anew and fully active surface in the case of fouling or deactivation by other means. By using a hematin-modified carbon paste electrode, the applied potential shifted negatively compared with that of unmodified carbon paste electrode or a glassy carbon electrode. The shift in potential changed the reaction processes and effectively stabilized the chemiluminescent signal during successive measurements. Under this condition, the signal was stable during 3 hours of continuous operation. The log-log plots of the emitted light intensity vs. luminol concentration and hydrogen peroxide concentration were linear over the region 10(-8)-10(-3) mol L-1 with a correlation coefficient of 0.999 and 3.9 x 10(-6)-10(-3) mol L-1 with a correlation coefficient of 0.994, respectively. Application of this method for other chemiluminescent and bioluminescent systems is suggested.

Effect of hydrogen bonds on optical nonlinearities of inorganic crystals

This work probes the role of hydrogen bonds (such as O-H ... O and N-H ... O) in some inorganic nonlinear optical (NLO) crystals, such as HIO3, NH4H2PO4 (ADP), K[B5O6(OH)(4)] . 2H(2)O (KB5) and K2La(NO3)(5) . 2H(2)O (KLN), from the chemical bond standpoint. Second order NLO behaviors of these four typical inorganic crystals have been quantitatively studied, results show hydrogen bonds play a very important role in NLO contributions to the total nonlinearity. Conclusions derived here concerning the effect of hydrogen bonds on optical nonlinearities of inorganic crystals have important implications with regard to the utilization of hydrogen bonds in the structural design of inorganic NLO crystals. (C) 1999 Elsevier Science B.V. All rights reserved.

Preparation and luminescent properties of inorganic polymer nano - Structured hybrid films doped with rare earth complexes

The inorganic/polymer hybrid films with good luminescent properties have been obtained by the sol - gel process via incorporating the polymer component doped with rare earth complexes. These films exhibit good toughness and transparency. Their fluorescence spectra and lifetimes indicate that they all have the characteristic luminescence of the central rare earth ions. The lifetimes of these films are longer than those of pure complexes. TEM have showed that the rare earth complexes are dispersed homogeneously in SiO2/PVB interpenetratiny networks, and the dispersed size is between 20 and 30 nn.

Abnormal IR spectra of CO adsorbed on the surface of glass carbon electrode modified with polypyrrole film with platinum microparticles

Abnormal IR spectra of CO adsorbed at the surface of glass carbon electrode modified with polypyrrole film with Pt microparticles are reported.

Electrochemical study of the interfacial characteristics of redox-active viologen thiol self-assembled monolayers

The electrochemical behavior of the electroactive self-assembled monolayers (SAMs) of thiol-functionalized viologen, CH3(CH2)(9)V2+(CH2)(8)SH, where V2+ is a viologen group, on the gold electrodes is examined by cyclic voltammetry and electrochemical a.c. impedance. A monolayer of viologen is immobilized on the gold electrode surface via the Au-S bond and the normal potentials corresponding to the two successive one-electron transfer processes of the viologen active centers are -310 mV and -652 mV (vs. Ag/AgCl) in 0.1 mol l(-1) phosphate buffer solution (pH 6.96) respectively. These results suggest that the viologen SAMs are stable and well-behaved monolayers. The experimental impedance data corresponding to different forms of viologen group have been fitted to equivalent electrical circuits, and the surface capacitances and resistances have been given. The heterogenous electron transfer rates of the first and the second redox processes are 7.57 s(-1) and 1.49 s(-1) respectively through a.c. impedance.

Electrochemical identification of intermediate forms of urea denaturation of horse heart cytochrome c

The electrochemical identification of the urea denaturation of horse heart cytochrome c in bulk solution at the 4,4'-dithiodipyridine-modified gold electrode is reported. The results are similar to the three-step transitions of equilibrium studies (Myer et al., Biochemistry, 19 (1980) 199) of urea denaturation of cytochrome c in bulk solution. This method permits a clear resolution of which of the three steps of urea denaturation is electrochemically related. In addition, by analysing the effects of urea on the structural forms of cytochrome c and on the solution properties, as well as the cyclic voltammetric responses of the protein, the individual forms of the urea denaturation of cytochrome c can be understood. The results reflect the superposition of protein denaturation on the electrode surface and in solution.

Chemical Bonding between Heteropoly Acid and Oxygen-containing Groups on the Surface of Activated Carbon

In order to define the force of heteropoly acids on absorbed activated carbon surface, IR spectra of 12-silicotungstic acid (SiW12) and 12-tungstophosphoric acid (PW12) absorbed on activated carbon and in oxygen-containing organic compound solutions were studied. Based on the IR spectra and UV characteristics of the heteropoly acids in various chemical conditions, the chemical bonding between heteropoly acid and oxygen-containing gropus on the surface of activated carbon was suggested.

VISCOSITY AND FLOW PROPERTIES OF CONCENTRATED-SOLUTIONS OF CHITOSAN WITH DIFFERENT DEGREES OF DEACETYLATION

The effects of the degree of deacetylation (DD) on the viscosity and flow behaviour of concentrated solutions of chitosan were investigated using 0.2 M CH3COOH and 0.2 M CH3COOH/0.1 M CH3COONa aqueous solutions as solvents. The results indicated that the

CATALYTIC BEHAVIOR OF METAL-IONS LOCATED AT DIFFERENT SITES OF HETEROPOLYCOMPOUNDS

It was discovered experimentally that heteropolymolybdophosphoric acids (HPA) with Keggin and Dawson structure are inactive for H2O2-decomposition, while their salts (Fe3+, Cu2+, Co2+ and Mn2+) all possess more activity. It could be concluded that the act