VILMARIA APARECIDA RIBEIRO
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Artigo IPEN-doc 24380 Palladium nanoparticles supported on phosphorus-doped carbon for ethanol electro-oxidation in alkaline media2018 - SILVA, JULIO C.M.; FREITAS, ISABEL C. de; NETO, ALMIR O.; SPINACE, ESTEVAM V.; RIBEIRO, VILMARIA A.Palladium nanoparticles supported on carbonVulcan XC72 (Pd/C) and on phosphorus-doped carbon (Pd/P-C) were prepared by an alcohol reduction process. X-ray diffractograms of Pd/C and Pd/P-C showed the typical face-centered cubic (fcc) structure of Pd. The crystallite sizes of Pd fcc phase were around 8 nm for both samples. X-ray photoelectron spectroscopy revealed to Pd/C and Pd/P-C that Pd was found predominantly in the metallic state and to Pd/P-C, the presence of P increases the amount of oxygen on the electrocatalyst surface. The activity and stability of the electrocatalyts for ethanol electro-oxidation in alkalinemedium was investigated by cyclic voltammetry and chronoamperometry experiments. The peak current density on Pd/P-C was 50% higher than on Pd/C, while the current density measured after 30 min at − 0.35 V vs. Hg/ HgO was 65% higher on Pd/P-C than on Pd/C. The enhancement of the catalytic activity of Pd/P-C electrocatalyst might be related to the presence of higher amounts of oxygen species on the surface, which could contribute to the oxidation of intermediates formed during ethanol electro-oxidation process.Artigo IPEN-doc 24370 Platinum nanoparticles supported on nitrogen-doped carbon for ammonia electro-oxidation2017 - RIBEIRO, VILMARIA A.; FREITAS, ISABEL C. de; O. NETO, ALMIR; SPINACE, ESTEVAM V.; SILVA, JULIO C.M.Pt nanoparticles supported on carbon (Pt/C) and nitrogen-doped carbon (Pt/NC) were prepared by an alcohol-reduction process and used for ammonia electro-oxidation in alkaline media. Nitrogen-doped carbons were prepared by thermal treatment of urea and Carbon Vulcan XC72 at 800 C under argon atmosphere. The obtained materials showed the presence of face centered cubic structure of Pt and mean particle sizes in the range of 3e3.7 nm. X-ray photoelectron spectroscopy results revealed that Pt/NC 5 (carbon prepared with 5% of urea) presents more Pt on the surface than Pt/C, and the nanoparticles are predominantly in the metallic state. The electrocatalytic activity was investigated by cyclic voltammetry and chronoamperometry experiments. Pt/NC materials showed a higher electrocatalytic activity for ammonia electro-oxidation than Pt/C, whereby the material Pt/NC 5 showed the peak current density 161% higher than Pt/C. The increase of activity might be related to the high electrochemically accessible area of Pt/NC and the improvement on the interaction with water due to the nitrogen onto the support which could contribute to the oxidation of intermediate products from ammonia electro-oxidation.Artigo IPEN-doc 23085 Preparation of PtRu/C Electrocatalysts by borohydride reduction for methanol oxidation in acidic and alkaline medium2017 - SANTOS, MONIQUE C.L. dos; DUTRA, RITA M.; RIBEIRO, VILMARIA A.; SPINACE, ESTEVAM V.; OLIVEIRA NETO, ALMIRPtRu/C electrocatalysts were performed according to the borohydride reduction method and characterized by X–ray diffraction (XRD), energy dispersive analysis (EDX), transmission electron microscopy, cyclic voltammetry (CV) and polarization curves in alkaline and acidic medium. The X-ray diffraction (XRD) of PtRu/C showed Pt peaks attributed to the face-centered cubic (fcc) structure and a shift in Pt(fcc) peaks indicated that Ru was incorporated into Pt lattice. TEM results showed mean particles sizes in the range of 2.0-4.0nm for all electrocatalysts prepared: therefore, the borohydride reduction process was considered effective for the preparation of PtRu/C electrocatalysts with a different atomic ratio. The activity for the methanol oxidation in acidic and alkaline media was investigated at room temperature, by cyclic voltammetry and chronoamperometry. Cyclic voltammetry and chronoamperometry studies showed that PtRu/C (50:50) had superior performance for methanol oxidation, compared with other electrocatalysts prepared considering acidic and alkaline studies. The currents values observed for alkaline media were higher than those observed for acidic media. Polarization curves, also, showed PtRu/C (50:50) with superior performance for methanol oxidation, when compared with Pt/C, and this improvement of performance could be associated with the occurrence of the bifunctional mechanism and electronic effect.