Methanol tolerant FeTPP-Pt/C Co-catalysts for the electroreduction of oxygen

It was found for the first time that iron tetraphenylporphyrin (FeTPP)-Pt/C showed the good activity for the electroreduction of oxygen and methanol tolerant ability. Their performances were related to the heat-treatment temperature.

Carbon ceramic electrodes bulk-modified with nanoparticles of ferrocenebutyrate-intercalated Mg-Al layered double hydroxide

Ferrocenebutyrate-intercalated layered double hydroxide (FcLDH) was prepared by the coprecipitation method and characterized by PXRD, FTIR, TEM and elemental analysis. FcLDH nanoparticles in deionized water were deposited onto the surface of graphite powder to yield graphite powder-supported FcLDH, which was subsequently dispersed into methyltrimethoxysilane-derived gels to fabricate surface-renewable, stable, rigid carbon ceramic electrodes containing the electroactive ferrocenyl group. Cyclic voltammetric study revealed that peak currents of the FcLDH-modified electrode were diffusion-con trolled in 0.1 mol l(-1) KCl aqueous solution. In addition, the formal potential of the modified electrode is related to the activity of chloride ion with a Nernst slope of 56 mV per decade.

Cupric hexacyanoferrate nanoparticle modified carbon ceramic composite electrodes

Graphite powder-supported cupric hexacyanoferrate (CuHCF) nanoparticles were dispersed into methyltrimethoxysilane based gels to produce a conducting carbon ceramic Composite, which was used as electrode material to fabricate surface- renewable CuHCF-modified electrodes. Electrochemical behavior of the CuHCF-modifled carbon ceramic composite electrodes was characterized using cyclic and square-wave voltammetry. Cyclic voltammograms at various scan rates indicated that peak currents were surface-confined at low scan rates. In the presence of glutathione, a clear electrocatalytic response was observed at the CuHCF-modified composite electrodes. In addition, the electrodes exhibited a distinct advantage of reproducible surface-renewal by simple mechanical polishing on emery paper, as well as ease of preparation, and good chemical and mechanical stability in a flowing stream.

Carbon ceramic electrodes modified with sub-micron particles of new methylene blue (NMB) intercalated alpha-zirconium phosphate

New methylene blue-intercalated a-zirconium phosphate (NMBZrP) was synthesized in the presence of n-butylamine and characterized by powder XRD, FTIR, TEM and elemental analysis. Sub-micron particles of NMBZrP in deionized water were apt to deposit onto the surface of graphite powder to yield graphite powder-supported NMBZrP, which was subsequently dispersed into methyltrimethoxysilane-derived gels to fabricate surface-renewable, stable, rigid carbon ceramic electrodes containing new methylene blue. Cyclic voltammetric studies revealed that peak currents of the NMBZrP-modified electrode were surface-confined at low scan rates but diffusion-controlled. at high scan rates. In addition, NMBZrP immobilized in a carbon ceramic matrix presented a two-electron, three-proton redox process in acidic aqueous solution in the pH range from 0.52 to 3.95.

Photoelectrochemical reduction of CO2 mediated with methylviologen at roughened silver electrodes

The photoelectrocatalytic effect for the reduction of CO2 mediated with methylviologen (MV) was studied at mercury, polished silver and roughened silver electrodes using electrochemical and surface-enhanced Raman scattering (SERS) techniques. A large photoelectrocatalytic effect for the reduction of CO2 in the presence of MV was observed at the roughened silver electrode, whereas there was only a very small photoelectrocatalytic current at a more negative potential on mercury and polished silver electrodes. The SERS spectra of MV in the presence and absence of CO2, along with the electrochemical results, demonstrate that the surface adsorbed complexes, MV+ -Ag and MV0-Ag, played a role as the mediator for photoinduced electron transfer to CO2 in the solution. The results also suggest that the surface plasmon resonance of the nanoscale silver particle contributes to the overall photoelectrocatalytic effect on a roughened silver electrode.

Study of color centers and trace oxygen in KMgF3 : Eu single crystal

Using the Bridgeman-Stockbarger method, the KMgF3:EU2+ single crystal was grown. The color centers in unirradiated KMgF3:Eu crystal were studied. By thermal annealing, we confirmed the 422-nm emission resulted from color centers and oxygen centers, and we proved the energy transfer from EU2+ to color centers. From spectra, the relative oxygen content in crystal was calculated, and the relationships of oxygen displacing fluorine were studied.

Fabrication and electrochemical behaviors of multilayers composed of heteropholyanions and poly(diallyldimethylammonium chloride) on 4-aminothiophenol modified gold electrodes

Multilayer films composed of heteropolyanions (HPAS, SiMo11 VO405-) and cationic polymer poly(diallyldimethylammonium chloride) on 4-aminothiophenol self-assembled-monolayer were fabricated by electrochemical growth. Growth processes of the composite films were characterized by cyclic voltammetry. The results prove the third redox peak of Mo increases more rapidly, otherwise the other Mo redox peaks increase very slowly when the number of layers of heteropolyanions is greater. The peak potentials of composite films shift linearly to negative position with higher pH, which implies that protons are involved in the redox processes of HPA. The investigation of electrocatalytic behaviors of composite films shows a good catalytic activity for the reductions of HNO2 and BrO3-. Catalytic currents increase with increasing number of layers of heteropolyanions, moreover, the catalytic currents have a good linear relationship with the concentrations of BrO3-.

Electrocatalytic reduction of O-2 and H2O2 at the glass carbon electrode modified with microperoxidase-11

Electrocatalytic reduction of O-2 and H2O2 at the glass carbon electrode modified with microperoxidase-11 immobilized with Nafion film has been studied by means of cyclic voltammetry and rotating disk electrode techniques. The modified electrode shows high catalytic activity toward the reduction of both O-2 and H2O2. The rate constants of Oz and H2O2 reduction at the modified electrode have been measured and compared. It is found that O-2 undergoes a four-electron reduction at the modified electrode and the catalytic activity for the reduction of O-2 is dependent on the pH of the solutions.

Fabrication of nanometer-sized electrodes and tips for scanning electrochemical microscopy

A novel method for fabrication of nanometer-sized electrodes and tips suitable for scanning electrochemical microscopy (SECM) is reported. A fine etched Pt wire is coated with polyimide, which was produced by polymerization on the Pt surface initiated by heat. This method can prepare electrodes with effective radii varying from a few to hundreds of nanometers. Scanning electron microscopy, cyclic voltammetry, and SECM were used to characterize these electrodes. Well-defined steady-state voltammograms could be obtained in aqueous or in 1,2-dichloroethane solutions. Ibis method produced the nanoelectrodes with exposed Pit on the apex, and they can also be employed as the nanotips for SECM investigations. Different sizes of Pt nanotips made by this method were employed to evaluate the kinetics of the redox reaction of Ru(NH3)6(3+) on the surface of a large Pt electrode by SECM, and the standard rate constant kappa (o) of this system was calculated from the best fit of the SECM approach curve. This result is similar to the values obtained by analysis of the obtained voltammetric data.

Simple preparation method of multilayer polymer films containing Pd nanoparticles

A simple route to the fabrication of multilayer films containing Pd nanoparticles is described. Following layer-by-layer assembly of PdCl42- and polycation, QPVP-Os (a quaternized poly(4-vinylpyridine) complexed with [Os(bpy)(2)Cl](2+/+)), on 4-aminobenzoic acid-modified glassy carbon electrodes, the three-dimensional Pd nanoparticle multilayer films are directly formed on electrode surfaces via electrochemical reduction of PdCl42- sandwiched between polymers. The growth of PdCl42- is easy on electrode surfaces by electrostatic interaction, and the assembly processes are monitored by cyclic voltammetry and UV-vis spectroscopy. The depth profile analyses by X-ray photoelectron spectroscopy verify the constant composition of the Pd nanoparticle multilayer films. Atomic force microscopy proves that the as-prepared Pd nanoparticles are uniformly distributed with an average particle diameter of 3-7 mn. The resulting Pd nanoparticle multilayer-modified electrode possesses high catalytic activity for the reduction of dissolved oxygen and oxidation of hydrazine compounds in aqueous solution.

Photosensitization of TiO2 nanoparticulate thin film electrodes by CdS nanoparticles

Surface photovoltage spectra (SPS) measurements of TiO2 show that a large surface state density is present on the TiO2 nanoparticles and these surface states can be efficiently decreased by sensitization using US nanoparticles as well as by suitable heat treatment. The photoelectrochemical behavior of the bare TiO2 thin film indicates that the mechanism of photoelectron transport is controlled by the trapping/detrapping properties of surface states within the thin films, The slow photocurrent response upon the illumination can be explained by the trap saturation effect. For a TiO2 nanoparticulate thin film sensitized using US nanoparticles, the slow photocurrent response disappears and the steady-state photocurrent increases drastically, which suggests that photosensitization can decrease the effect of surface states on photocurrent response.

Rapid electron propagation through molecular wire monolayers sandwiched between two gold electrodes

Conjugated bisthioester 1 was synthesized applying Sonogashira coupling reactions. Using self-assembly in combination with nanoparticles deposition techniques, we developed a novel method to fabricate a "gold electrode-molecular wire monolayers-gold nanoparticles" sandwich-like structure. Rapid electron propagation through this sandwich-like structure was observed by cyclic voltammetry and ac impedance measurements.

Production of active oxygen species from Taxus cuspidata induced by far-UV radiation

In order to understand the role of active oxygen species in mediating plant injuries induced by far-UV radiation, seedlings of Taxus cuspidata Sieb. et Zucc. were irradiated by far-UV rays in laboratory for 4 weeks. The production of organic free-radicals in detached needles, and the production of O-2(radical anion) and O-1(2) in isolated chloroplasts were detected weekly by electron spin resonance (ESR) to evaluate their relative importance. The results show that the cumulative effect of far-UV irradiation, is best indicated by the production of organic free radicals in the needles, O-2(radical anion) production in chloroplasts is the next. The enhancement of O-1(2) production in chloroplasts by the cumulative far-UV irradiation seems to be not so important as O-2(radical anion) in mediating injuries induced by, far-UV radiation because of its high background value.

Impedance study of (PEO)(10)LiClO4-Al2O3 composite polymer electrolyte with blocking electrodes

A composite solid polymer electrolyte (SPE) of (PEO)(10)LiClO4-Al2O3 was prepared and Pt and stainless steel(SS) blocking electrodes were used for an impedance study. It was found that the semicircle in the high frequency range and the straight line in the low frequency range depend upon different blocking electrodes and polarization potentials applied in the experiments. In the equivalent circuit. two constant phase elements (CPE) have been used instead of the pure geometrical and double layer capacitances. respectively. A theoretical line calculated from their estimated values has a good correlation with the experiment data. Moreover. the equivalent circuit also can be used to explain the impedance properties of Pt and stainless steel (SS) blocking electrodes both in the high and the low frequency ranges. (C) 2001 Elsevier Science Ltd. All rights reserved.

Surface photovoltage spectra and photoelectrochemical properties of semiconductor-sensitized nanostructured TiO2 electrodes

Three kinds of TiO2 nanostructured thin films and their CdS-sensitized films, consisting of different sizes of TiO2 nanoparticles prepared with different methods, have been investigated. The surface photovoltage spectra (SPS) measurements indicate that the density of surface states on TiO2 is likely dependent upon the details of prepared methods. TiO2 particles prepared from basic sol have more surface states than that prepared from acidic sol. When the TiO2 thin films prepared using the TiO2 sols were sensitized by CdS particles, the SPS responses relative to the surface states on TiO2 from 350 to 800 nm were decreased. The photoelectrochemical properties of nanostructured TiO2 electrodes suggest that the fewer the surface states and the smaller the particle sizes of TiO2, the larger the photocurrent response. For CdS sensitized TiO2 thin film electrode, it is shown that the semiconductor sensitization is an efficient way to decrease the influence of surface states on the charge separation, and can improve the intensity of photocurrent response. (C) 2001 Elsevier Science B.V. All rights reserved.