Simple preparation method of Pd nanoparticles on an Au electrode and its catalysis for dioxygen reduction

A simple method for the fabrication of Pd nanoparticles is described. The three-dimensional Pd nanoparticle films are directly formed on a gold electrode surface by simple electrodeposition at -200 mV from a solution of 1 M H2SO4+0.01 mM K2PdCl4. X-Ray photoelectron spectroscopy verifies the constant composition of the Pd nanoparticle films. Atomic force microscopy proves that the as-prepared Pd nanoparticles are uniformly distributed with an average particle diameter of 45-60 nm. It is confirmed that the morphology of the Pd nanoparticle films are correlated with the electrodeposition time and the state of the Au substrate. The resulting Pd-nanoparticle-film-modified electrode possesses high catalytic activity for the reduction of dissolved oxygen in 0.1 M KCl solution. Freshly prepared Pd nanoparticles can catalyze the reduction of O-2 by a 4-electron process at -200 mV in 0.1 M KCl, but this system is not very stable. The cathodic peaks corresponding to the reduction of O-2 gradually decrease with potential cycling and at last reach a steady state. Then two well-defined reduction peaks are observed at -390 and -600 mV vs. Ag/AgCl/KCl (sat.). Those two peaks correspond to a 2-step process for the 4-electron reduction pathway of O-2 in this neutral medium.

Self-assembly of the pre-formed inclusion complexes between cyclodextrins and alkanethiols on gold electrodes

A new kind of self-assembled monolayer (SAM) formed in aqueous solution through the pre-formed inclusion complexes (abbreviated CD . C-n) between alpha-, beta-cyclodextrins (CDs) and alkanethiols (CH3(CH2)(n-1)SH, n = 10, 14 and 18) was prepared successfully on gold electrodes. High-resolution H-1 NMR was used to confirm the formation of CD . C-n. X-ray photoelectron spectroscopy, cyclic voltammetry and chronoamperometry were used to characterize the resulting SAMs (denoted as M-CD . Cn). It was found that M-CD . Cn were more stable against repeated potential cycling in 0.5 M H2SO4 than SAMs of CH3(CH2)(n-1)SH (denoted as M-Cn), with a relative sequence of Mbeta-CD . Cn > Malpha-CD . Cn > M-Cn. In addition, an order of blocking the electron transfer between gold electrodes and redox couples (both Fe(CN)(6)(3-) and Ru(NH3)(6)(3+)) in solution, M-CD . C10 > M-CD . C14 > M-CD . C18, was observed. A plausible explanation is provided to elucidate some of the observations. (C) 1997 Elsevier Science S.A.

EFFECTS OF ANODIC-OXIDATION ON THE SURFACE-STRUCTURE OF HIGHLY ORIENTED PYROLYTIC-GRAPHITE REVEALED BY IN-SITU ELECTROCHEMICAL SCANNING-TUNNELING-MICROSCOPY IN H2SO4 SOLUTION

Effects of the potential of anodic oxidation and of potential cycling on the surface structure of a highly oriented pyrolytic graphite (HOPG) electrode were observed by in situ electrochemical scanning tunnelling microscopy (ECSTM) in dilute H2SO4 solution with atomic resolution. With potential cycling between -0.1 V and 1.8 V vs. Ag/AgCl (sat. KCI), some atoms on the top layer of HOPG protrude out of the base plane, and the graphite lattice of these protrusions is still intact but is strained and expanded. With further potential cycling, some protrusions coalesced and some grew larger, and an anomalous superperiodic feature was observed (spacing 90 Angstrom with a rotation 30 degrees relative to atomic corrugations) which superimposed on the atomic corrugation of HOPG. On the topmost of these protrusions, some atoms form oxides and others are still resolved by the ECSTM image. With potential cycling between -0.1 V and + 2.0 V vs. Ag/AgCl (sat. KCl), damage to freshly cleaved HOPG surface is more serious and fast, some ridges are observed, the atomic structure of the HOPG surface is partially and then completely damaged due to the formation of oxide. We also found that anodic oxidation occurred nonuniformly on the surface of HOPG near defects during potential cycling.

PREPARATION OF MODIFIED ELECTRODE WITH MOLYBDOPHOSPHATE ANION AND ITS ELECTROCATALYSIS FOR BROMATE REDUCTION

A molybdophosphate anion modified electrode has been prepared in 2 M sulfuric acid solution containing PMo12O403- by electrochemical cycling scan or simple adsorption on a glassy carbon electrode anodized before modification. The film electrode obtained is very stable upon potential cycling in acid solution. The catalytic effect of the film for reduction of bromate was investigated in detail.

IN-SITU SCANNING-TUNNELING-MICROSCOPY IMAGE OF A HIGHLY ORIENTED PYROLYTIC-GRAPHITE ELECTRODE MODIFIED WITH POTASSIUM BIS(11-MOLYBDOSILICATO) DYSPROSATE(III) IN SODIUM-SULFATE SOLUTION

The variation in molecule adsorption mode on pretreated highly oriented pyrolytic graphite electrodes, modified with the title complex K10H3[Dy(SiMo11O39)(2)] by cyclic voltammetry in the title complex solution, was observed in situ by electrochemical scanning tunnelling microscopy (ECSTM) with molecular resolution in sodium sulphate solution. According to the ECSTM images and the known molecular structure we conclude that the adsorption mode of the title complex modified electrode changed during potential cycling from ''vertical'' to ''inclined'' and then ''horizontal'' or ''flat'' mode, i.e. the title complex adsorbed on the surface of electrode by one ligand of the complex at first, then began to incline and was finally adsorbed by two ligands of the complex. This result indicates that the adsorption mode on the modified electrode surface changed during potential cycling in the sulphate solution and a much more stable molecular layer was formed. The change in adlattice of adsorbates on the modified electrode surface from hexagonal to rectangular was also observed by ECSTM. A plausible model was given to explain this process.

ELECTROCHEMICAL-BEHAVIOR OF MOLIBDOSILICIC HETEROPOLY COMPLEX WITH DYSPROSIUM AND ITS DOPED POLYPYRROLE FILM-MODIFIED ELECTRODE

In this paper, the electrochemical behaviour of molibdosilicic heteropoly complex with dysprosium K10H3[Dy(SiMo11O39)(2)]. xH(2)O [denoted as Dy(SiMo11)(2)] was studied. Voltammetric behavior of this complex was greatly influenced by pH of solutions. The polypyrrole (PPy) film doped with this complex was prepared by electropolymerization of pyrrole in the presence of Dy(SiMo11)(2) under potential cycling conditions. The microenvironment within the PPy film has an effect on the electrochemical behavior of Dy(SiMo11)(2) entrapped in the film. The film electrode can catalyze the reduction of ClO3- and BrO3-.

PREPARATION AND CHARACTERIZATION OF ISOPOLYMOLYBDIC ANIONS DOPED POLYPYRROLE (IPOMO/PPY) FILM ELECTRODE

Isopolymolybdic anion doped polypyrrole film electrode was prepared by electrochemical polymerization of pyrrole in 0.5 mol.L-1 H2SO4 aqueous solution containing isopolymolybdic anions. The film thus prepared has good stability upon potential cycling in s

STUDY OF A 1/12 PHOSPHOMOLYBDIC ANION DOPED POLYPYRROLE FILM ELECTRODE AND ITS CATALYSIS

A phosphomolybdic anion doped polypyrrole (PMo12O403- + PPy) film electrode has been prepared by electrochemical polymerization of pyrrole in an aqueous solution of 0.5 mol l-1 H2SO4 or 0.5 mol l-1 KNO3 containing PMo12O403- anions, and characterized by scanning electron microscopy and in-situ UV-visible spectroelectrochemical methods. The film electrode obtained is very stable upon potential cycling in acidic solution, but not in neutral solution. The catalytic effect of the film electrode on the reduction of ClO3- and BrO3- was studied.

情绪干扰下焦虑水平对执行抑制的影响机制——事件相关电位研究

Behavioral inhibition model suggests the generation of anxiety is related with over-inhibition. For knowing about anxiety better, we used event-related potential (ERP) technique to explore the underlying mechanism of executive inhibition under the emotional distracter in high and low trait-anxious groups. Firstly, we set up the Chinese affective picture system (CAPS) as the stimuli of subsequent experiments. Secondly, we screened the high and low trait-anxious participants using the State-Trait Anxiety Inventory. In the first ERP study, a modified oddball paradigm was used with the positive, neutral and negative pictures as novel stimuli and the potentials evoked by three types pictures were analyzed. In the second ERP study, the same paradigm with higher task load was employed to examine the interaction of anxious level and emotion. Main results as follows: 1. CAPS consisted of 852 pictures was assessed via three dimensionalities, valence, arousal and dominance. The standard deviation of scores on valence and dominance was more than the standard deviation of scores on dimension of arousal. Scatter plot showed that the score distributing on the dimension of valence and arousal was wide in CAPS. 2. In both high and low trait-anxiety groups, the amplitudes of N2 and P3 of negative pictures were greater and smaller respectively as compared with neutral and positive pictures, which suggested all participants no matter what anxious level required more inhibition processing to negative information than others. 3. With increasing of task load, the P3 amplitudes of negative pictures in high anxious group were reduced relative to neutral pictures. In addition, in high anxious group, the P3 amplitudes of positive pictures had the same changes as those of negative ones. Whereas, the reduced P3 of positive pictures were not observed in low anxious group. The results showed the high anxious participants employed the same inhibitory strategy to the positive distracter as the negative distracter, which possibly the over-inhibition processing was involved in this group. 4. Dipole source analysis found cingulate may be involved in executive inhibition processing. In sum, as for the inhibition, high and low anxious group both is sensitive to negative information. However, in the high load situation, due to the shortness of cognitive resources, the high anxious individual represents the general sensitivity to all emotional information. These results gave the electrophysiological evidence for over-inhibition in high trait-anxiety group.

X-ray emission from charge exchange of highly-charged ions in atoms and molecules

Charge exchange followed by radiative stabilization are the main processes responsible for the recent observations of X-ray emission from comets in their approach to the Sun. A new apparatus was constructed at JPL to measure, in collisions of HCIs with atoms and molecules, (a) absolute cross sections for single and multiple charge exchange, and (b) normalized X-ray emission cross sections. The ions are produced by the JPL HCI Facility and passed through a neutral-gas target cell. The product charge states are analyzed by a retarding potential difference technique. Results are made absolute by measuring target pressure, and incident and product ion currents. X-rays emitted from the product ions are detected with a Ge solid-state detector having a resolution of approximately 100 eV. X-ray astronomy has taken major steps forward with the recent launch of the high-resolution satellites Chandra and Newton. The cross sections reported herein are essential for the development of the solar wind comet interaction models inspired by these observations.

A new route to synthesize high degree polythiophene in a room temperature melt medium

Conducting polymers suffer from folds and kinks because of random nucleation and solvation of a free radical cation to yield a cross linked/disordered polymer and therefore a solvent free electrochemical polymerization in a room temperature melt medium is adopted to yield a high degree polymer with high electronic conductivity. Electropolymerization of thiophene was performed on platinum/ITO substrates using cyclic voltametry or galvenostatic mode in chloroaluminate room temperature melt medium to obtain a reddish brown free standing film which can be peeled off from the electrode surface after a minimum of 10 cycles. The conductivity was found to be around 102 S/cm. The degree of polymerization was calculated to be around 44 from IR studies. A layered structure supportive for high degree of polymerization was witnessed from potential step technique. From UV spectra the charge carriers were found to be bipolarons. The morphology of the film was found to be crystalline from SEM and XRD studies. Capacitative impedance properties for doped samples were interpreted from impedance spectroscopy.

Studies on polypyrrole film in room temperature melt

A bluish-black shining free standing polypyrrole film (PPy) of electronic conductivity 130 S cm-1 has been prepared by electrochemical oxidative polymerization of pyrrole on Pt/transparent glass conducting electrode resistance 15 O cm-1, using a room temperature melt as an electrolyte, composed of 1:3 stoichiometric ratio of cetyl pyridinium chloride and anhydrous aluminum chloride at 0.58 V versus Al wire as a reference electrode. The film possessed a charge transfer resistance of 132 O, and showed two absorption peaks at 457 and 1264 nm in the UV-vis–NIR diffused reflectance spectra. The morphology of the film was hexagonal. The potential step technique suggested a layered structure. This thin film can easily be peeled off from the electrode surface after three cycles and can be used for various applications like dissipation of electrostatic charge, battery electrode materials, solid electrolytic capacitor, electrochromic windows and displays, microactuators etc. It was also characterized by IR, thermal and SEM studies.

In situ FTIRS investigations of surface processes of Rh electrode - Novel observation of geminal adsorbates of carbon monoxide on Rh electrode in acid solution

With the help of in situ multi-step FTIR Spectroscopy, two types of adsorbed geminal CO have been observed for the first time at an electrochemically modified Rh electrode. A doublet band of two broad peaks at 2166 and 2112cm is assigned to geminal CO on Rh surface oxide (or hydroxide) produced by the electrochemical modification process, and a doublet band of two peaks near 2103 and 2033cm is ascribed to geminal CO on surface clusters of Rh formed by reduction of Rh surface oxide. Based on the evolution of FTIR spectra with the electrode potential, the surface processes of a Rh electrode, subjected to a potential cycling treatment at 1.5Vs between -0.275 and 2.4V for 2min, have been elucidated. The present results at the solid/liquid electrochemical interface were compared with those obtained at the solid/gas interface, and consistent conclusions were achieved.

Anaerobic Digestibility of Microalgae : Fate and Limitations of Long Chain Fatty Acids in the Biodegradation of Lipids

La digestion anaérobie est un processus biologique dans lequel un consortium microbien complexe fonctionnant en absence d’oxygène transforme la matière organique en biogaz, principalement en méthane et en dioxyde de carbone. Parmi les substrats organiques, les lipides sont les plus productifs de méthane par rapport aux glucides et aux protéines; mais leur dégradation est très difficile, en raison de leur hydrolyse qui peut être l’étape limitante. Les algues peuvent être une source importante pour la production de méthane à cause de leur contenu en lipides potentiellement élevé. L’objectif de cette étude était, par conséquent, d’évaluer la production en méthane des microalgues en utilisant la technique du BMP (Biochemical méthane Potential) et d’identifier les limites de biodégradion des lipides dans la digestion anaérobie. Le plan expérimental a été divisé en plusieurs étapes: 1) Comparer le potentiel énergétique en méthane des macroalgues par rapport aux microalgues. 2) Faire le criblage de différentes espèces de microalgues d’eau douce et marines afin de comparer leur potentiel en méthane. 3) Déterminer l'impact des prétraitements sur la production de méthane de quelques microalgues ciblées. 4) Identifier les limites de biodégradation des lipides algaux dans la digestion anaérobie, en étudiant les étapes limitantes de la cinétique des lipides et de chacun des acides gras à longues chaines. Les résultats ont montré que les microalgues produisent plus de méthane que les macroalgues. Les BMP des microalgues d'eau douce et marines n'ont montré aucune différence en termes de rendement en méthane. Les résultats des prétraitements ont montré que le prétraitement thermique (microonde) semblait être plus efficace que le prétraitement chimique (alcalin). Les tests de contrôle du BMP faits sur l'huile de palme, l’huile de macadamia et l'huile de poisson ont montré que l'hydrolyse des huiles en glycérol et en acides gras à longues chaines n'était pas l'étape limitante dans la production de méthane. L'ajout de gras dans les échantillons de Phaeodactylum dégraissée a augmenté le rendement de méthane et cette augmentation a été corrélée à la quantité de matières grasses ajoutées.

Electrocatalysis of oxygen reduction on carbon-supported Pt-Co nanoparticles with low Pt content

The oxygen reduction reaction (ORR) was investigated on carbon-supported Pt-Co nanoparticle electrocatalysts with low Pt content in alkaline electrolyte. High resolution transmission electron microscopy, In situ X-ray absorption spectroscopy, and X-ray diffraction analysis evidenced large structural differences of the Pt-Co particles depending oil the route of the catalyst synthesis. It was demonstrated that although the Pt-Co materials contain low amounts of Pt, they show very good activities when the particles are formed by a Pt-rich shell and a Pt-Co core, which was obtained after submitting the electrocatalyst to a potential cycling in acid electrolyte. The high activity of this material was due to a major contribution from its higher surface area, as a result of the leaching of the Co atoms from the particle Surface. Furthermore, its high activity was ascribed to a minor contribution from the electronic interaction of the Pt atoms, at the particle surface, and the Co atoms located in the beneath layer, lowering the Pt cl-band center. As these electrocatalysts presented high activity for the ORR with low Pt content, the cost of the fuel cell cathodes could be lowered considerably. (c) 2009 Elsevier B.V. All rights reserved.