Effects of Alloyed and Oxide Phases on Methanol Oxidation of Pt-Ru/C Nanocatalysts of the Same Particle Size

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

Alloys and oxides on carbon-supported Pt-Sn electrocatalysts for ethanol oxidation

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

The Extent on the Nanoscale of Pt-Skin Effects on Oxygen Reduction and Its Influence on Fuel Cell Power

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

Effect of niobium dopant on fatigue characteristics of BiFeO3 thin films grown on Pt electrodes

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Electrocatalysis of hydrogen evolution reaction on Pt electrode surface-modified by S-2 chemisorption

Kinetic studies of hydrogen evolution reaction (HER) at the surface of Pt in alkaline conditions, reported in this paper, show that electrocatalytic activity is enhanced after adsorption of S-2 ions. EIS and steady-state polarization curve data pointed to an undoubted improvement in performance with the Pt-S cathode that was attributed to higher adsorbed hydrogen coverage. Experimental findings suggested an increase in the electronic density of the modified surface sites that may strengthen the interaction between H2O and the adsorption site and, consequently, accelerates the Volmer step. (c) 2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.

Nature of defects for bismuth layered thin films grown on Pt electrodes

The authors investigated the influence of defects on the piezoelectric and dielectric properties of Bi4Ti3O12 (BIT), SrBi4Ti4O15 (SBTi) and CaBi4Ti4O15 (CBTi144) thin films by x-ray photoemission spectroscopy measurements. In the SBTi film, Sr which is a nonpolarizable ion restricting the movement of Ti4+ ions and thus leads to a low piezoresponse. Meanwhile, the oxygen environment is quite different in the BIT and CBTi144 films exhibiting excellent piezoelectric properties. The piezoelectric coefficient and the dielectric behavior were larger for a-b axis oriented than for c axis-oriented films due to the defects created during the films crystallization. (c) 2007 American Institute of Physics.

Electrochemical oxidation of methanol on Pt nanoparticles dispersed on RuO2

Pt-modified RuO2 was prepared by a sol-gel procedure on titanium substrates in the form of thin films of similar to2-mum thickness. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses showed that these films actually consist of Pt nanoparticles dispersed in RuO2 and that neither metallic Ru nor Pt-Ru alloy are present on the surface. Electrodes with different Pt:Ru nominal compositions were prepared and their electrocatalytic activity for the oxidation of methanol was investigated by potential sweeps and chronoamperometry. The results obtained show an enhancement effect for methanol oxidation that can be interpreted as associated to the formation of hydrous oxides on the RuO2 surface.

Sol-gel prepared Pt-modified oxide layers: Synthesis, characterization, and electrocatalytic activity

Thin films of pure RuO2 and IrO2 and mixed Ru0.5Ir0.5O2 oxide modified with Pt particles were prepared by a sol-gel method in the form of thin films of similar to 2 mu m thickness on Ti substrates. Surface morphology of these Pt- modified oxides was examined by scanning electron microscopy and was found to exhibit a significant influence of the chemical composition of the oxide matrix. Element mapping showed homogeneous distribution of the metals. X- ray diffraction and X- ray photoelectron spectroscopy analyses showed that these films consist of metallic Pt particles dispersed in an oxide matrix. Cyclic voltammetry in acid solutions showed that the sol- gel prepared layers have relatively high Pt surface areas. The electrocatalytic activity of these materials toward the anodic oxidation of formaldehyde and methanol was compared in terms of onset potential and current density and was found to follow the sequence: Pt- Ru0.5Ir0.5O2/ Ti > Pt- RuO2/ Ti > Pt- IrO2/ Ti.

Electrodeposited thin mercury films on Pt-Ir alloy electrodes

Mercury thin films prepared by electrochemical deposition on Pt-Ir alloy and after partial removing of mercury at different temperatures were studied by means of an interferometric surface mapping microscope and by X-ray photoelectronic spectroscopy. Mercury film samples having mercury partially removed by anodic stripping at a potential more positive than the corresponding peak in the voltammogram were also studied using the same techniques. For blank samples the surface topographic studies showed well defined grain boundaries. Mercury film samples when heated up to different temperatures showed as material is removed and that the surface roughness decreases as the temperature increases. For samples heated up to 800 degrees C the surface roughness is approximately the same that for the blank. A model for the interphase of volumetric mercury electrodeposited on a Pt-Ir alloy has been proposed using samples both electrochemically and thermally removed of their Hg coatings. The model includes a layered three-region structure, containing at least two Pt-Hg intermetallics: PtHg4 and PtHg2. A substrate modified region, iridium rich, has also been detected. (C) 1999 Elsevier B.V. S.A. All rights reserved.

Thermal analysis and electrochemical study of Hg reactions on Pt-30% Ir alloy electrode

Thermogravimetry (TG), cyclic voltammetry (CV) and other analytical techniques were used to study the reactions of mercury with Pt-30% Ir alloy. The results allowed to suggest that an electrodeposited mercury film interacts with the substrate and when subjected to heat or electrochemical removal at least four mass loss steps or five peaks appeared during the mercury desorption process. The first two steps were attributed to Hg(0) removal probably from the bulk and from the adsorbed monolayer which wets the electrode surface. These two processes are responsible for peaks D and F in the cyclic voltammograms. The last two peaks (G, H) in CV were ascribed to the intermetallic compound decomposition. In TG curves, the last two steps were attributed to the PtHg4 (third step), and PtHg2 decomposition followed by Hg removal from the subsurface. The PtHg2 was formed by an eutectoide reaction: PtHg -> PtHg2+Hg(Pt-Ir). The Hg diffused to the subsurface was not detectable by cyclic voltammetry.

Synthesis and X-ray structure of the dinuclear platinum(II) complex with saccharin {K[Pt(sac)(3)(H2O)] center dot H2O}(2): Studies on its antiproliferative activity in aqueous solution

Synthesis and X-ray structure of a dinuclear platinum(II) complex with the ligand saccharin(sac) are described. The structure shows two approximately square-planar platinum centers. Each platinum atom is coordinated to one water molecule and three N-bonded saccharinate ligands. The two centers are linked through two potassium atoms. Each potassium atom interacts with six oxygen atoms from hydration and coordinated water molecules and from carbonyl and sulfonate groups of the ligands. It is suggested that, in aqueous solution, the dimeric structure of the complex is dissociated and the monomeric species K[Pt(sac)(3)(H2O)] is formed. The complex was dissolved in water and submitted to in vitro cytotoxic analyses using HeLa cells (human cervix cancer). It was shown that the monomeric complex elicited a potent cytotoxic activity when compared to the vehicle-treated cells. The IC50 value for the monomeric complex is 6.8 mu M, a little bit higher than that obtained for cisplatin. (c) 2007 Elsevier B.V. All rights reserved.

Influence of seed particle frequency on the phase formation and on the microstructure of 0.88 PZN-0.07 BT-0.05 PT ceramic

The Pechini method as well as the simultaneous addition of seeds particles and dopant solutions of BaTiO3 (BT) and PbTiO3 (PT) were used to prepare the perovskite phase 0.88 PZN-0.07 BT-0.05 PT. To study the influence of seed particle frequency on the synthesis of the PZN ceramic, two ranges of seed particle size were used: the range from 30 to 100 nm, termed small seed particles (frequency of 10(15) particles/cm(3)); and the range from 100 to 900 nm, termed large seed particles (frequency of 10(13) particles/cm(3)). The crystalline nuclei size influenced the calcining process, the sintering process and the microstructure. Samples prepared with lower seed frequency displayed more amount of pyroclore phase, need higher temperatures for sintering and showed a more heterogeneous microstructure with poor dielectric properties. (C) 2000 Elsevier B.V. Ltd and Techna S.r.l. All rights reserved.

Anodic oxidation of formaldehyde on Pt-modified SnO2 thin film electrodes prepared by a sol-gel method

Pt-modified SnO2 electrodes were prepared onto titanium substrates in the form of thin films of similar to2 mum at different temperatures in the range from 200 to 400degreesC. Surface morphology was examined by scanning electron microscopy (SEM). It was found that Pt-SnO2 sol-gel layers are significantly rough and have a low porosity. X-ray diffraction (XRD) studies showed that the films consist of Pt nanoparticles with average size varying from about 5 to 10 nm, depending on the preparation temperature, and amorphous tin oxide. X-ray photoelectron spectroscopy (XPS) was employed to determine the superficial composition of the electrodes and demonstrated the presence of Sn4+ in all the samples. XPS spectra of the Pt 4f electrons showed the presence of Pt in the zero-valence state as well as in ionic forms. The general electrochemical behavior was characterized by cyclic voltammetry in 1 mol l(-1) HClO4 and the electrocatalytic activity towards the oxidation of formaldehyde was investigated by potential sweeps and chronoamperometry. The results obtained show that the Pt-SnO2/Ti system exhibits a significant catalytic activity for the oxidation of formaldehyde, with an onset potential below 0.1 V. (C) 2004 Elsevier Ltd. All rights reserved.

Effects of post-annealing on the dielectric properties of Au/BaTiO3/Pt thin film capacitors

Barium titanate thin films were prepared by the polymeric precursor method and deposited onto Pt/Ti/SiO2/Si substrates. X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FT-IR) and micro-Raman spectroscopy were used to investigate the formation of the BaTiO3 perovskite phase. Afterwards, the films were submitted to post-annealing treatments in oxygen and nitrogen atmospheres at 300 degreesC for 2 h, and had their dielectric properties measured. It was observed that the electric properties of the thin films are very sensitive to the nature of the post-annealing atmosphere. This study demonstrates that post-annealing in an oxygen atmosphere increases the dielectric relaxation phenomenon and that post-annealing in a nitrogen atmosphere produces a slight dielectric relaxation. (C) 2004 Elsevier B.V All rights reserved.

Synthesis and electrical characterization of CaBi2Nb2O9 thin films deposited on Pt/Ti/SiO2/Si substrates by polymeric precursor method

We report the successful deposition of CaBi2Nb2O9 (CBN) thin films on platinum coated silicon substrates by polymeric precursor method. The CBN thin films exhibited good structural, dielectric and CBN/Pt interface characteristics. The leakage current of the capacitor structure was around 0.15 A cm(-2) at an applied electric field of 30 kV cm(-1). The capacitance-voltage measurements indicated good ferroelectric polarization switching characteristics. The typical measured small signal dielectric constant and the dissipation factor at a frequency of 100 kHz were 90 and 0.053, respectively. The remanent polarization and the drive voltage values were 4.2 C cm(-2) and 1.7 V at an applied voltage of 10 V. No significant fatigue was observed at least up to 10(8) switching cycles. (c) 2005 Elsevier B.V. All rights reserved.