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.