Cadmium UPD on Au was studied by voltammetric and microgravimetric measurements. In the oxide formation/reduction potential region, a mass increasing/decreasing of 32 ng cm-2 was associated to incorporation/elimination of one oxygen per active site. The modifications promoted in the voltammetric and mass profiles by 10-5 M Cd(ClO4)2 are restricted to potentials more negative than 0.4 V. After a 120 s potential delay at 0.05 V, the positive sweep reveals an anodic peak with charge of 40 muC cm-2 and mass decrease of 22 ng cm-2, associated to Cd ads dissolution. Sulphate or chloride was added to the solution without significant influence, due to the low coverage with Cd or anions.

The underpotential deposition of Cd on polycrystalline Pt and Au was studied by voltammetry at stationary and rotating ring-disc electrodes. On Pt, the Cd ads dissolution peaks overlap those related to the oxidation of Hads, thus hindering the precise evaluation of desorption charges. A model proposed to calculate such charges from voltammetry at stationary electrodes revealed a value of 285 muC cm-2 for the monolayer dissolution, which corresponds to a coverage of 90% with Cd ads presenting an electrosorption valence of 0.5. Rotating ring-disc experiments fully confirmed such values. The misfit between atomic radii of Cd and Pt justifies the less-than-100% coverage. On the other hand, on Au, the absence of Hads simplifies the procedure for determination of dissolution charges for the Cd monolayer. Here, a value of only 41 muC cm-2 was calculated, which corresponds to a maximum coverage of 15%, with the electrosorption valence of 0.5. The results obtained in the collecting experiments with the rotating electrode are in complete agreement with those values.

Este trabalho consiste no estudo de t?cnicas de rob?tica e de Realidade Virtual (RV) para desenvolver um simulador que possa ser empregado nas escolas de rob?tica, possuindo uma visualiza??o adequada e uma forma de intera??o simples e intuitiva. Para isto, foi desenvolvido um Ambiente Virtual (AV), em linguagem C++, utilizando OpenGL. Foram incorporados recursos de RV para melhorar a visualiza??o e facilitar a intera??o do usu?rio com o programa. A avalia??o do ambiente foi realizada atrav?s da an?lise dos resultados obtidos nos experimentos realizados com usu?rios, em que foram gerados relat?rios autom?ticos para as quest?es quantitativas, e preenchidos question?rios para as quest?es qualitativas. Os resultados mostraram que o uso de RV auxilia na execu??o da tarefa, pois melhora a visualiza??o, reduzindo o tempo total e melhorando a precis?o.

Different mass ratio proportions of PtSn (m/m) electrocatalysts with 20% metal loading on a carbon support were prepared for use in ethanol:methanol solutions oxidation reactions. PtSn/C (3:1) (91% alloy degree, lattice parameter of 0.399 nm and mean crystallite size 4.8 nm) presented the best activity for oxidation of mixed solutions. The highest normalized current (ethanol:methanol 80:20) was 4.2 mA mgPt-1 (measured after 1800 seconds at 0.5 V). Therefore, the PtSn/C (3:1) electrocatalyst with an atomic ratio of 65:35 enhanced both the electronic effect and bifunctional mechanism in (ethanol:methanol 80:20), which resulted in the formation of CO2 at low potentials, as well as the highest amount of by-products than ethanol and methanol.

This work describes the preparation of Pt/C, PtxSny/C and PtxSny(CeO2 nanorods/C) nanoparticle catalysts synthesized by the chemical reduction method via sodium borohydride for the ethanol oxidation reaction. Using X-ray diffractogram analysis, it was verified that no alloy formation occurred between platinum (Pt) and tin (Sn). The distribution of the nanoparticles in the support occurs in a more agglomerated form for the materials containing Sn and CeO2 nanorods (NR). The electrocatalyst Pt3Sn1_20%NRCeO2/C was highlighted in CO-stripping experiments because it showed the lowest onset potential for CO oxidation and the highest value for the electrochemically active surface area. The other electrochemical experiments for ethanol oxidation showed similar activities for the Pt3Sn1/C and Pt3Sn1_20%NRCeO2/C electrocatalysts. The observed effect can be associated with defects in the structure of the CeO2 nanorods, the electrochemical active surface area, and the properties of the CeO2 nanorods related to enhancing the generation of oxy-hydroxy species at lower potentials compared to PtSn/C electrocatalysts, which increased the CO oxidation as measured using stripping experiments. For this reason, it is possible to both use less platinum and to obtain behavior close to that of PtSn/C electrocatalysts for ethanol oxidation reaction (EOR).

In this work, the gas diffusion electrode (GDE) cathode of Vulcan XC72 carbon modified with nanoparticles of WO2.72 (WO2.72 / Vulcan XC72) was used for H2O2 electrogeneration and degradation of 350 mL of Orange II (OII) and Sunset Yellow FCF (SY) azo dyes by electro-Fenton (EF) and photoelectro-Fenton (PEF) processes with different Fe2+ initial content (1.00, 0.50 and 0.25 mmol L-1). The WO2.72 / Vulcan XC72 GDE electrolyzed approximately 3 times more H2O2 than the Vulcan XC72 GDE. Decolorizations and mineralizations of the dye solutions were more efficient at higher concentrations of Fe2+. The decolorization decay showed pseudo-first-order kinetics. The most promising decolorization results obtained at processes of WO2.72 / Vulcan XC72 cathode combined with Pt anode (100% color removal of OII and SY at 30 and 20 min of electrolysis with 1.00 mmol L-1 Fe2+, respectively). The best mineralization achieved in trials of WO2.72 / Vulcan XC72 cathode combined with boron-doped diamond (BDD) anode (82% total organic carbon (TOC) removal of OII by PEF / 1.00 after 3 h and 90% TOC removal of SY by PEF / 0.50 after 4 h). It was found that SY decolorization was faster and mineralization showed a similar yield independent of oxidized dye.