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Lisbon, Portugal

Eugenio S.,University of Lisbon | Rangel C.M.,Fuel Cells and Hydrogen Unit | Vilar R.,University of Lisbon | Quaresma S.,University of Lisbon
Electrochimica Acta | Year: 2011

The electrochemical behaviour of trivalent chromium (Cr3+) in 1-butyl-3-methylimidazolium tetrafluoroborate [BMIm][BF4] ionic liquid solutions was studied by cyclic voltammetry and chronoamperometry. The reduction of Cr3+ occurs in two steps, Cr3+ to Cr 2+ and Cr2+ to Cr0, respectively. The first step is quasi-reversible with a diffusion coefficient of Cr3+ in solution of 3.13 × 10-8 cm2 s-1 at 303 K and 25.8 × 10-8 cm2 s-1 at 358 K, estimated from cyclic voltammetry data. Black chromium films were electrodeposited on copper, stainless steel and carbon steel substrates at a constant potential of -1.5 V vs Pt quasi-reference electrode. The films consist of aggregates of nanosized particles. The coatings in the as-deposited condition present an amorphous structure but after annealing for 4 h, a nanocrystalline Cr2O3 phase is formed, with an average crystallite size of 17 nm. © 2011 Elsevier Ltd. All rights reserved. Source


Soares C.O.,C.C.M.M. | Silva R.A.,Fuel Cells and Hydrogen Unit | Carvalho M.D.,C.C.M.M. | Jorge M.E.M.,C.C.M.M. | And 3 more authors.
Electrochimica Acta | Year: 2013

LaNiO3 film electrodes were prepared by brush painting using nickel-foam supports in order to increase its surface area available for electrochemical reactions. Loadings varying between 20 and 140 mg cm -2 were tested. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to evaluate the coatings roughness (Rf) and morphology (φ) factors, complemented by optical microscopy observations. The values obtained from the two methods are in excellent agreement. The Rf values, ranging from 848 ± 50 to 4260 ± 60, are within the highest in the open literature. A simulation, of the effect of the oxide loading on the coatings Rf values, was performed using just the experimental values of the roughness factors for oxide free foam and pelleted electrodes. It was found that the increase of oxide loading causes a quasi linear increase of the electrodes active surface area. Simulated values were in excellent agreement with the experimental roughness factors and pore resistances obtained by CV and EIS. The electrodes were tested for oxygen evolution. © 2012 Elsevier Ltd. All Rights Reserved. Source


Soares C.O.,University of Lisbon | Carvalho M.D.,University of Lisbon | Melo Jorge M.E.,University of Lisbon | Gomes A.,University of Lisbon | And 3 more authors.
Journal of Applied Electrochemistry | Year: 2012

LaNiO 3 coatings on nickel-foam supports were prepared by brush painting. The electrochemical properties were investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Comparative studies were performed with LaNiO 3-pelleted electrodes. The roughness factors were determined by CV and found to be 5,208 ± 350 and 4,037 ± 250 for the pelleted and coated electrodes, respectively. EIS measurements confirm the results obtained by CV. Values lower than 0.3 were calculated for the morphology factors for both electrodes, indicating low electrochemical porosity. The experimental method used in this work to synthesise the oxide coupled with the use of Ni foam as support has proved to be very effective in producing oxide electrodes with surface areas higher than those referred to in relevant literature. © 2012 Springer Science+Business Media B.V. Source


De Sa A.I.,Fuel Cells and Hydrogen Unit | Eugenio S.,University of Lisbon | Quaresma S.,University of Lisbon | Rangel C.M.,Fuel Cells and Hydrogen Unit | And 2 more authors.
Thin Solid Films | Year: 2011

The electrodeposition of gold from a HAuCl4.3H2O solution in 1-butyl-1-methyl-pyrrolidinium dicyanamide is reported in the present paper. A cyclic voltammetry study of the electrochemical behaviour of the plating solution showed that the reduction of gold occurs by a two-step process. Gold thin films were obtained by electrodeposition on nickel substrates under potentiostatic control at a constant potential of - 1 V, for temperatures from 293 to 353 K and deposition times of 1500 and 4500 s. The films prepared at 293 and 333 K consist of 9-15 nm diameter polyhedral particles aggregated in clusters 50-250 nm in diameter. The films deposited at 353 K consist of a quasi-continuous film of nanoparticles covered by nanosized dendrites. This morphology evolves towards a globular structure with increasing deposition time. © 2011 Elsevier B.V. All rights reserved. Source


Soares C.O.,University of Lisbon | Carvalho M.D.,University of Lisbon | Melo Jorge M.E.,University of Lisbon | Gomes A.,University of Lisbon | And 3 more authors.
Portugaliae Electrochimica Acta | Year: 2011

In this work LaNiO 3 oxide was prepared by a self-combustion method using citric acid. The electrodes were obtained by coating a nickel foam support with the oxide suspension. Optical microscopy and cyclic voltammetry were used on the electrodes characterization. The evaluation of the electrodes electrocatalytic activity, towards the oxygen evolution reaction in alkaline medium, was performed by means of steady state measurements. The reaction follows a first order kinetics, with respect to OH- concentration, with Tafel slopes close to 40 mV, for low overpotentials. Based on the apparent and real current densities it was possible to conclude that the increase on the electrode activity, when compared with the published data, is mostly related to geometric factors. This fact has been associated with the high electrode/electrolyte contact area provided by the foam nickel substrate. Synergetic effects between the Ni foam and the perovskite oxide cannot be discarded. Source

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