Evidence for diffusional coupling in electrochemical thin layers: implications for surface coverage calibration via electrochemical infrared spectroscopy

The time dependence of the concentration of CO2 in an electrochemical thin layer cavity is studied with Fourier transform infrared spectroscopy (FTIR) in order to evaluate the extent to which the thin layer cavity is diffusionally decoupled from the surrounding bulk electrolyte. For the model system of CO on Pt(111) in 0.1 M HClO4, it is found that the concentration of CO2, formed by electro-oxidation of CO, equilibrates rapidly with the surrounding bulk electrolyte. This rapid equilibration indicates that there is diffusion out of the thin layer, even on the short time scales of typical infrared experiments (1-3 min). However, since the measured CO2 absorbance intensity as a function of time is reproducible to within 10%, a new time-dependent method for surface coverage calibration using solution-phase species is proposed.

The electrochemical effect of acid functionalisation of carbon nanotubes to be used in sensors development

The electrochemical behaviour of multi-walled carbon nanotubes was compared with that of glassy carbon, and the differences were investigated by cyclic voltammetry and electrochemical impedance spectroscopy before and after acid pre-treatment. The electrochemical techniques showed that acid functionalisation significantly improves the electrocatalytic properties of carbon nanotubes. These electrocatalytic properties enhance the analytical signal, shift the oxidation peak potential to a less positive value, and the charge-transfers rate increase of both dopamine and K(4)[Fe(CN)(6)]. The functionalisation step and the resulting appearance of edge planes covered with different chemical groups were confirmed by FTIR measurements. Carbon nanotubes after acid pre-treatment are a potentially powerful analytical tool for sensor development. (C) 2010 Elsevier B.V. All rights reserved.

Direct Electrochemical Determination of Glyphosate at Copper Phthalocyanine/Multiwalled Carbon Nanotube Film Electrodes

A copper phthalocyanine/multiwalled carbon nanotube film-modified glassy carbon electrode has been used for the determination of the herbicide glyphosate (Gly) at -50 mV vs. SCE by electrochemical oxidation using differential pulse voltamtnetry (DPV). Cyclic voltammetry and electrochemical impedance spectroscopy showed that Gly is adsorbed on the metallic centre of the copper phthalocyanine molecule, with formation of Gly-copper ion complexes. An analytical method was developed using DPV in pH 7.4 phosphate buffer solution, without any pretreatment steps: Gly was determined in the concentration range of 0.83-9.90 mu mol L(-1), with detection limit 12.2 nmol L(-1) (2.02 mu g L(-1))

Electrochemical Behavior of Verapamil at Graphite-Polyurethane Composite Electrodes: Determination of Release Profiles in Pharmaceutical Samples

A solid graphite-polyurethane composite electrode has been used to determine release profiles of verapamil, a calcium-channel blocker. The electro-oxidation process was characterized by cyclic voltammetry and electrochemical impedance spectroscopy and showed no adsorption of analyte or oxidation products, unlike at other carbon-based electrodes. Quantification gave linear ranges up to 40molL-1 with cyclic voltammetry and detection limits of 0.7molL-1 by differential pulse and square-wave voltammetry. Commercial product samples were successfully analyzed with results equal to those from spectrophotometry. Because no electrode surface renewal is needed, this electrode material has many advantages.

Exploiting the versatility of taste sensors based on impedance spectroscopy

The versatility of sensor arrays made from nanostructured Langmuir-Blodgett (LB) and layer-by-layer (LBL) films is demonstrated in two ways. First, different combinations of sensing units are employed to distinguish the basic tastes, viz. sweet, sour, bitter, and salty tastes, produced, respectively, by small concentrations (down to 0.01 g/mol) of sucrose, HCl, quinine, and NaCl solutions. The sensing units are comprised of LB and/or LBL films from semiconducting polymers, a ruthenium complex, and sulfonated lignin. Then, sensor arrays were used to identify wines from different sources, with the high distinguishing ability being demonstrated in principal component analysis (PCA) plots. Particularly important was the fact that the sensing ability does not depend on specific interactions between analytes and the film materials, but a judicious choice of materials is, nevertheless, required for the materials to respond differently to a given sample. It is also shown that the interaction with the analyte may affect the morphology of the nanostructured films, as indicated with scanning electron microscopy. For instance, in wine analysis these changes are not irreversible and the original film morphology is retrieved if the sensing unit is washed with copious amounts of water, thus allowing the sensor unit to be reused.

Detection of glucose and triglycerides using information visualization methods to process impedance spectroscopy data

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

Analysis of the Al-PANI interfaces by complex impedance spectroscopy

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Stability of cp-Ti and Ti-6Al-4V alloy for dental implants as a function of saliva pH - an electrochemical study

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

The Role of Lipopolysaccharide on the Electrochemical Behavior of Titanium

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Detection of phenolic compounds using impedance spectroscopy measurements

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

Influence of spraying parameters on the electrochemical behaviour of HVOF thermally sprayed stainless steel coatings in 3.4% NaCl

Stainless steel coatings obtained by High Velocity Oxygen Fuel (HVOF) were characterized using optical (OM) and scanning electron microscopy (SEM), electron probe micro-analysis, X-ray diffraction (XRD), open-circuit potential (E-OC) measurements, electrochemical impedance spectroscopy (EIS) and polarisation tests. Differences among coated steels were mainly related with the gun-substrate distance parameter (310 nm for samples A and B and 260 min for C and D). The open-circuit potential values measured for all the samples after 18 h of immersion in aerated and unstirred 3.4% NaCl solution were: - 0.334, - 0.360, - 0.379 and - 0.412 V vs. Ag/AgCl,KClsat. for samples A to D, respectively. For EIS measurements, Nyquist plots showed higher capacitive semi-circle for samples sprayed at longer distance, indicating higher corrosion resistance in NaCl solution. (c) 2005 Elsevier B.V. All rights reserved.

Electrochemical behaviour of heat-treated Al-Zn-Mg alloys in chloride solutions containing sulphate

The electrochemical corrosion and passivation of Al-5Zn-1.7Mg-0.23Cu-0.053Nb alloys, submitted to different heat treatments (cold-rolled, annealed, quenched and aged, and quenched in two steps and aged), in sulphate-containing chloride solutions, has been studied by means of cyclic polarization, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), and X-ray photoelectron spectroscopy (XPS). The cyclic polarization curves showed that sulphate addition to the chloride solution produced a poor reproducible shift of the breakdown potential to more positive potentials. The repassivation potentials, much more reproducible, and practically separating the passive from the pitting potential region, were slightly displaced in the negative direction with that addition. When the alloys were potentiodynamically polarized in the passive potential region, sulphate was incorporated in the oxide film, thus precluding chloride ingress. In addition, Zn depletion was favoured, whereas Mg losses were avoided. Different equivalent circuits corresponding to different alloys and potentials in the passive and pitting regions were employed to account for the electrochemical processes taking place in each condition. This work shows that sulphate makes these alloys more sensitive to corrosion, increasing the fracture properties of the surface layer and favouring the pitting attack over greater areas than chloride alone. (C) 2002 Elsevier B.V. Ltd. All rights reserved.

Electrochemical and structural characterization of heat-treated Cr3C2-NiCr coatings

The influence of heat-treatments on the electrochemical behavior of thermal spray Cr3C2-NiCr coatings prepared by high velocity oxygen fuel (HVOF) was studied in NaCl solution, at 25 degrees C, using open-circuit potential (E-OC) and electrochemical impedance spectroscopy (EIS) measurements. Coating characterization were performed before and after the heat-treatments and electrochemical tests by scanning electron microscopy, X-ray diffraction, and Auger electron spectroscopy. In addition to the changes in the original powder composition occurring during HVOF process, heat-treatment performed at 450 degrees C caused no significant changes in electrochemical response compared with untreated sample, and at 760 degrees C the main difference was the formation of a thin and defective layer of Cr2O3 at the coating surface, which increased the total impedance at the first day of immersion. Higher influence on the electrochemical was noted for samples treated at 880 degrees C, which also showed higher E-OC and total impedance, and lower corrosion current. This behavior was interpreted considering the formation of a chromium oxide layer on the coating surface, dissolution and decomposition of smaller carbide particles and their surface enrichment with Cr due to C diffusion and dissolution into the matrix, and possible Ni, Cr, and Fe diffusion to coating/substrate interface. (c) 2006 the Electrochemical Society.

WC-CoCr coatings sprayed by high velocity oxygen-fuel (HVOF) flame on AA7050 aluminum alloy: electrochemical behavior in 3.5% NaCl solution

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

Electrochemical stability and corrosion resistance of Ti-Mo alloys for biomedical applications

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