Preparation and characterization of ordered intermetallic platinum phases for electrocatalytic applications

Ordered intermetallic phases of Pt with several transition metals have been prepared and their electrocatalytic properties studied. In light of these tests it is proposed that these catalysts could be used as electrodes in fuel cells, as they combine an excellent capacity to adsorb organic fuels at the Pt sites with low susceptibility to being poisoned by intermediates and reaction products at the transition-metal sites. An experimental procedure used to obtain the four intermetallic phases Pt-M (M = Mn, Pb, Sb and Sn) is described. The phases thus produced were characterized by X-ray diffraction, scanning electron microscopy with surface analysis by energy-dispersive X-ray spectrometry, scanning tunneling microscopy and X-ray photoelectron spectroscopy. The data thus obtained support the conclusion that the method described here is highly effective for the preparation of Pt-M phases featuring a range of structural and electronic modifications that will allow a useful relation to be established between their physicochemical properties and predicted electrocatalytic activity. (C) 2007 Elsevier Ltd. All rights reserved.

Determination of isoniazid in human urine using screen-printed carbon electrode modified with poly-L-histidine

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Síntese e caracterização de nanocatalisadores 'PtV'/C e 'PtCr'/C para cátodos de células a combustível de baixa temperatura

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Desenvolvimento e teste de nanocatalisadores a base de Pd para a redução de oxigênio

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Rapid preparation of alpha-FeOOH and alpha-Fe2O3 nanostructures by microwave heating and their application in electrochemical sensors

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Sol-gel thin-film based mesoporous silica and carbon nanotubes for the determination of dopamine, uric acid and paracetamol in urine

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Aplicação de métodos computacionais no estudo das fases intermetálicas ordenadas pt-sn

Fuel cells are a very promising solution to the problems of power generation and emission of pollutant to the environment, excellent to be used in stationary application and mobile application too. The high cost of production of these devices, mainly due to the use of noble metals as anode, is a major obstacle to massive production and deployment of this technology, however the use of intermetallic phases of platinum combined with other metals less noble has been evaluated as electrodes in order to minimize production costs and still being able to significantly improve the catalytic performance of the anode. The study of intermetallic phases, exclusively done by experimental techniques is not complete and demand that other methods need to be applied to a deeper understanding of the behavior geometric properties and the electronic structure of the material, to this end the use of computer simulation methods, which have proved appropriate for a broader understanding of the geometric and electronic properties of the materials involved, so far not so well understood.. The use of computational methods provides answers to explain the behavior of the materials and allows assessing whether the intermetallic may be a good electrode. In this research project was used the Quantum-ESPRESSO package, based on the DFT theory, which provides the self-consistent field calculations with great precision, calculations of the periodic systems interatomic force, and other post-processing calculations that points to a knowledge of the geometric and electronic properties of materials, which may be related to other properties of them, even the electrocatalytic. The electronic structure is determined from the optimized geometric structure of materials by analyzing the density of states (DOS) projected onto atomic orbital, which determines the influence of the electrocatalytic properties of the material... (Complete abstract click electronic access below)

Estudo da reação de oxidação de metanol sobre fases intermetálicas ordenadas de AuIn, AuSn e AuSb2 em meio alcalino

The present work assessment materials can be used as fuel cells electrocatalysts. The alkaline fuel cell though was less studied, has some advantages compared to the acid configuration. The materials assesment were Au polycrystalline and intermetallics ordered phases of AuIn, AuSn and AuSb2. Your electrocatalytic properties were studied across cyclic voltametry and chronoamperometry techniques in Sodium Hydroxide 0,15M and Metanol 0,15M solution. The results obtained show a more efficiency to intermetallic AuIn as electrocatalyst for the oxidation reaction of methanol in alkaline medium, it showed high levels of current density and on set potential less positive compared to Au polycrystalline. The intermetallic AuSn showed activity just higher concentrations of methanol. Except AuSb2, who represented himself unstable in alkaline media, the intermetallics AuIn and AuSn present a promising future as anode materials for the oxidation in alkaline medium

Electrochemical Properties of Oxo-Manganese Complex Biomimicking Enzyme Active Sites and Its Electrocatalytic Application for Dopamine Determination

This work describes the characterization of the [Mn2 IV,IVO2(terpy)2(H2O)2]4+ complex in aqueous solution by UV-vis spectrophotometry, cyclic voltammetry, and linear sweep voltammetry with a rotating disk electrode. The pH effect, potential scan rate, effect of perfluorosulfonate polymer, and anion of supporting electrode on the electrochemical behavior of the modified electrode for better performance were investigated. The potential peak of the modified electrode was linearly dependent upon the ratio [ionic charge]/[ionic radius]. The modified electrode exerted an electrocatalytic effect on dopamine oxidation in aqueous solution with a decrease in the overpotential compared with the unmodified glassy carbon electrode. This way, the modified electrode showed an enzymatic biomimicking behavior. Tafel plot analyses were used to elucidate the kinetics and mechanism of dopamine oxidation. © 2013 Springer Science+Business Media New York.

Influence of particle size on the properties of Pt-Ru/C catalysts prepared by a microemulsion method

Pt-Ru/C nanocatalysts were prepared by a microemulsion method using different values of water/surfactant molar ratio in order to get different particle sizes. Crystallite sizes and structural properties were determined by X-ray diffraction. Particle size and distribution were characterized by transmission electron microscopy and average composition was determined by energy-dispersive X-ray analysis. Thermogravimetric analysis was used to estimate the amount of supported metals. Differential scanning calorimetry measurements indicated the presence of hydrous ruthenium oxides in the as-prepared catalysts. Results for the oxidation of adsorbed CO as well as for methanol oxidation revealed significant differences in the behavior of the prepared catalysts. All together, the results demonstrate that the variation of particle size produces changes in other properties of the Pt-Ru/C catalysts and that to establish direct correlations between electrocatalytic activity and particle size is not possible because the effects of the different parameters cannot be separated. (c) 2007 the Electrochemical Society.

Surface structure and electronic properties of Pt-Fe/C nanocatalysts and their relation with catalytic activity for oxygen reduction

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Effects of heat treatments on the electrocatalytic activity of Pt-Ru/C for methanol oxidation

The Pt-Ru/C materials of this study were prepared by a microemulsion method with fixed water to surfactant molar ratio and heat treated at low temperatures, to avoid changes in the average particle size, in different atmospheres. All samples were characterized by X-ray diffraction (XRD) and the mean crystallite size was estimated by using Scherrer's equation. Catalysts morphology was characterized by transmission electron microscopy (TEM). Average composition was obtained by energydispersive X-ray analysis (EDX). The general electrochemical behavior was evaluated by cyclic voltammetry in 0.5 M sulfuric acid and the electrocatalytic activity towards the oxidation of methanol was studied in 0.5 M methanol acid solutions by potential sweeps and chronoamperometry. Oxidation of adsorbed CO was used to estimate the electrochemical active area and to infer the surface properties. ©The Electrochemical Society.

Electrochemical Properties of the Oxo-Manganese-Phenanthroline Complex Immobilized on Ion-Exchange Polymeric Film and Its Application as Biomimetic Sensor for Sulfite Ions

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Structural and Electrochemical Properties of Lutetium Bis-Octachloro-Phthalocyaninate Nanostructured Films. Application as Voltammetric Sensors

Thin films of the bis[2,3,9,10,16,17,23,24-octachlorophthalocyaninate] lutetium(III) complex (LuPc2Cl32) have been prepared by the Langmuir-Blodgett and the Langmuir-Schaefer (LS) techniques. The influence of the chlorine substituents in the structure of the films and in their spectroscopic, electrochemical and sensing properties has been evaluated. The pi-A isotherms exhibit a monolayer stability greater than the observed in the unsubstituted analogue (LuPc2), being easily transferred to solid substrates, also in contrast to LuPc2. The LB and LS films present a linear growth forming stratified layers, monitored by UV-VIS absorption spectroscopy. The latter also revealed the presence of LuPc2Cl32 in the form of monomers and aggregates in both films. The FTIR data showed that the LuPc2Cl32 molecules present a non-preferential arrangement in both films. Monolayers of LB and LS were deposited onto 6 nm Ag island films to record surface-enhanced resonance Raman scattering (SERRS), leading to enhancement factors close to 2 x 10(3). Finally, LB and LS films deposited onto ITO glass have been successfully used as voltammetric sensors for the detection of catechol. The improved electroactivity of the LB and LS films has been confirmed by the reduction of the overpotential of the oxidation of catechol. The enhancement of the electrocatalytic effect observed in LB and LS films is the result of the nanostructured arrangement of the surface which increases the number of active sites. The sensors show a limit of detection in the range of 10(-5) mol/L.

Development and application of a screen-printed electrode modified with MWCNT for the electrocatalytic detection of thiram

Interest in the electronic properties of carbon nanotubes has increased in recent years. These materials can be used in the development of electrochemical sensors for the measurement and monitoring of analytes of environmental interest, such as pharmaceuticals, dyes, and pesticides. This work describes the use of homemade screen-printed electrodes modified with multi-walled carbon nanotubes (MWCNT) for the electrochemical detection of the fungicide thiram. The electrochemical characteristics of the proposed system were evaluated using cyclic voltammetry, with investigation of the electrochemical behavior of the sensor in the presence of the analyte, and estimation of electrochemical parameters including the diffusion coefficient, electron transfer coefficient (α), and number of electrons transferred in the catalytic electro-oxidation. The sensor response was optimized using amperometry. The best sensor performance was obtained in 0.1 mol L-1 phosphate buffer solution at pH 8.0, where a detection limit of 7.9 x 10-6 mol L-1 was achieved. Finally, in order to improve the sensitivity of the sensor, square wave voltammetry (SWV) was used for thiram quantification, instead of amperometry. Using SWV, a response range for thiram from 9.9 x 10-6 to 9.1 x 10-5 mol L-1 was obtained, with a sensitivity of 30948 µA mol L-1, and limits of detection and quantification of 1.6 x 10-6 and 5.4 x 10-6 mol L-1, respectively. The applicability of this efficient new alternative methodology for thiram detection was demonstrated using analyses of enriched soil samples.