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Electrodeposition of Cu+PdO and (Cu-Pd) +PdO composites
No full textThe codeposition of PdO particles with a Cu matrix has been investigated with the aim of extending the composite deposition procedure to the preparation of materials potentially capable of catalyzing the low temperature combustion of methane. Cu+PdO composites with a low dispersed phase content were obtained from either basic pyrophosphate or acid sulfate baths. Codeposition of PdO particles with a Cu-Pd alloy matrix was effectively achieved by electrolyzing suspensions of PdO in solutions containing both Cu2+ and Pd 2+ ions, with large [Cu2+] / [Pd2+] ratios. (Cu-Pd) +PdO deposits with 20-25 Pd atom % were obtained in which only 1-2 atom % of Pd were alloyed in the matrix. These (Cu-Pd) +PdO composites were mechanically stable and highly porous throughout their thickness (their pore volume being ca. 60% of the total volume). Their true surface area was some thousands of times higher than their geometric area. © 2010 The Electrochemical Society
Electrochemical Behaviour of Porous PbO2Layers Prepared by Oxygen Bubble Templated Anodic Deposition
No full textPorous PbO2layers were produced from methanesulfonic acid or perchloric acid media, through an oxygen bubble templated anodic deposition process, i.e. by oxidizing Pb2+ions at large current densities, with simultaneous oxygen evolution. The effect of deposition current density, Pb2+concentration and nature of the acid on the deposit porosity (assessed through number of pores per unit surface area, average pore diameter, and void volume fraction) were investigated. Porous PbO2deposits obtained from both media consisted of the same mixture of α- and β-phases, although the corresponding compact deposits had significantly different structures (pure α-PbO2from methanesulfonic acid, a mixture of α- and β- PbO2from perchloric acid). The cycling behaviour of compact and porous PbO2layers in 1.0 M H2SO4was compared. During the first cycle, the reduction charge was much higher for porous than for compact layers, as a consequence of the different electrochemically active areas. For the former it depended on the layer thickness, while it was independent of it for the latter. Upon cycling, the charges exchanged by compact layers steadily increased, whereas those of porous layers, after an initial increase, slowly declined, but remained markedly higher
Spontaneous deposition of Pd onto Fe-Cr-Al alloys
No full textThe spontaneous deposition of Pd onto Fecralloy sheets and foams was studied. Pd deposits were obtained by immersion of Fecralloy samples in mildly acid, deaerated PdCl2solutions, at open circuit. Pd displaced all alloy elements and deposited onto the alloy which was initially coated by an oxides film and underwent transpassive dissolution. The Pd loading and the Pd surface area were determined as a function of experimental conditions, like the nature of the Fecralloy sample (sheets or foams of variable grade), the concentration of the PdCl2solution and the duration of the deposition. The results were compared to those obtained by depositing Pd onto Ni foams, with the same procedure. The Pd deposition rates were not much different on Fecralloy and Ni, but the Pd surface area per unit Pd mass was significantly higher for Ni than for Fecralloy. The Pd deposit morphology was influenced by the presence of passive oxides on the Fecralloy surface. The catalytic activity in methanol anodic oxidation depended only on the Pd surface area, irrespective of the nature of the support (Ni or Fecralloy). © 2012 Elsevier Ltd. All rights reserved
Oxygen bubble-templated anodic deposition of porous PbO<inf>2</inf>
No full textThe oxygen bubble-templated deposition of porous PbO2 was realized by anodizing Pb(II) solutions (in nitrate-acetate, sulfamate or methanesulfonate media) at large current density. This process is the anodic analogue of the more common hydrogen bubble-templated electrodeposition of porous metals. The porous PbO2 layers consisted of a mixture of α- and β-phases, in contrast to compact layers deposited at low current density (pure α-PbO2). The void volume fraction and surface roughness factor of porous PbO2 were estimated
Study of Cu, Cu-Ni and Rh-modified Cu porous layers as electrode materials for the electroanalysis of nitrate and nitrite ions
No full textThree porous materials (Cu, a Cu-Ni alloy with 70 at.% Cu and Rh-modified Cu) have been tested as electrodes for the electroanalysis of nitrate and nitrite ions, in either neutral or basic media, using mainly a flow injection technique. Porous Cu and Cu-Ni were prepared by electrodeposition at high current density, exploiting the transient template action of hydrogen bubbles. Rh-modified Cu electrodes were obtained from porous Cu, through a galvanic displacement reaction. All materials had a linear response for both nitrates and nitrites, at concentrations up to 10−3 M, at least. Sensitivities, detection limits and stability were determined. Compared with Cu, used as a benchmark, (i) Rh-modified Cu had higher sensitivity for nitrates, comparable sensitivity for nitrites, lower or comparable detection limits and overall better stability; (ii) Cu-Ni had lower sensitivity, but exhibited lower detection limits and more stable performance for most analyte/medium combinations
Nanoporous gold leaves: Preparation, optical characterization and plasmonic behavior in the visible and mid-infrared spectral regions
No full textConversion of porous PbO2layers through galvanic displacement reaction with Mn2 +ions
No full textThe galvanic exchange between Mn2 +ions and electrodeposited porous PbO2was studied to produce a porous oxide whose lower conductivity prevented its direct oxygen bubble-templated anodic deposition. Immersion of PbO2layers in acid acetate solutions of Mn2 +led to the formation of amorphous MnOxshell onto PbO2. Due to its amorphous nature, MnOxcould not be proved to be MnO2by XRD. However, MnOxwas cathodically stripped at the same potential as MnO2. The deposition of the MnOxshell onto PbO2enhanced the capacity of the porous electrodes
Reduction of Nitrate Ions at Rh-Modified Ni Foam Electrodes
No full textCommercial Ni foams were modified by spontaneous deposition of Rh nanoparticles, achieved by immersion of foam samples in acid, deaerated Na3RhCl6solutions, at open circuit. The surface area of the Rh deposits was estimated, for different Rh loadings, by measuring the H adsorption/desorption charge. The surface area per unit Rh mass was found to exceed 50 m2g-1, for loading values below 2 mg cm-3. The Rh-modified Ni foam electrodes were used as cathodes for the reduction of nitrate ions, and showed good catalytic activity, increasing with the Rh loading in a sublinear way; thus, the mass activity of the electrodes was higher at low loading. Prolonged electrolyses showed that the Rh-modified Ni foam electrodes underwent only moderate poisoning. Ion chromatography was used to assess the reaction products: irrespective of the Rh loading, ammonia was the main product, and nitrite accounted only for a few percent of the reduced nitrate. The beneficial effect of forcing a solution flow through the foam pores on the nitrate reduction current was shown. © 2013 Springer Science+Business Media New York
Electrochemical Impedance Spectroscopy study of the preparation of electrocatalysts through galvanic displacement reactions
No full textTo explore the potential of Electrochemical Impedance Spectroscopy (EIS) in monitoring a galvanic displacement reaction, the deposition of Rh by displacement of Ni has been investigated, using both Ni disc electrodes of small size and Ni foam electrodes. The Ni dissolution/Rh deposition rate has been evaluated from EIS data and compared with values obtained by an independent method. The variation of the electrode double layer capacity with the reaction duration, caused mainly by the growth of Rh deposits, has been compared with the time dependence of the Rh surface area assessed by cyclic voltammetry (through the measurement of the H desorption charge). The quality of the agreement between different methods and possible reasons for discrepancies are discussed. It is shown that EIS may be a useful tool in the study of galvanic displacement processes
Preparation of porous nanostructured Ag electrodes for sensitive electrochemical detection of hydrogen peroxide
No full textPorous Ag layers have been prepared by hydrogen bubble templated electrodeposition from an ammonium acetate bath, under application of a large current density (-2 A cm-2). SEM images of the layers show macroscopic porosity and a spongy dendritic structure, analogous to those observed for other porous metals/alloys deposited with a similar procedure. A deposition charge of 30 C cm-2produces a porous deposit with a mass of ca 1.7 mg cm-2. The roughness factor fris evaluated by impedance and from the charge density of Pb UPD; both methods provide estimates of frin the order of several hundreds but values obtained from impedance analysis are more than twice larger. Mass transport to the porous electrodes is studied by linear sweep voltammetry at stationary and rotating disk electrodes. In comparison with flat Ag cathodes, porous Ag electrodes show larger sensitivity, lower limit of detection and extended range of linear response in H2O2reduction
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