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      Synthesis of electrocatalysts by the Bönnemann method for the oxidation of methanol and the mixture H2/CO in a Proton Exchange Membrane Fuel Cell

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          Abstract

          The synthesis of ternary electrocatalysts Pt/Ru/Mo type were performed according to the Bönnemann method and characterized by the following techniques: energy dispersive analysis (EDX), X-rays diffraction (XRD), cyclic voltammetry (CV) and polarization curves (E vs. i) for the oxidation of H2, H2/CO and methanol in a Proton Exchange Membrane Fuel Cell (PEMFC). Catalysts structure consists of highly dispersed nanocrystals in carbon support, with an average particle size of 2 nm. The results of cyclic voltammetry suggest an enhancement of the catalyst electroactivity with the addition of cocatalysts. Polarization curves indicate that Pt/Ru/Mo systems could be employed as electrode material for PEM fuel cell for technological application.

          Translated abstract

          Novas formulações de eletrocatalisadores ternários do tipo Pt/Ru/Mo foram desenvolvidas pelo método de Bönnemann e caracterizadas pelas técnicas de análise por energia dispersiva de raios X (EDX), difração de raios X (XRD), voltametria cíclica (CV) e curvas de polarização (E vs. i), para a oxidação de H2 , mistura H2/CO e metanol em células a combustível tipo PEMFC. A estrutura dos catalisadores obtida é formada por nanocristais altamente dispersos na matriz de carbono, com 2 nm de tamanho médio da nanopartícula. Os resultados da voltametria cíclica sugerem um aumento considerável da eletroatividade do catalisador com a adição de cocatalisadores. A análise das curvas de polarização sugere que o catalisador ternário Pt/Ru/Mo pode ser interessante do ponto de vista tecnológico.

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          Ion Density Deviations in Polyelectrolyte Microcapsules: Influence on Biosensors

          Polyelectrolyte microcapsules loaded with fluorescent dyes have been proposed as biosensors to monitor local pH and ionic strength for diagnostic purposes. In the case of charged microcapsules, however, the local electric field can cause deviations of ion densities inside the cavities, potentially resulting in misdiagnosis of some diseases. Using nonlinear Poisson-Boltzmann theory, we systematically investigate these deviations induced by charged microcapsules. Our results show that the microcapsule charge density, as well as the capsule and salt concentrations, contribute to deviations of local ion concentrations and pH. Our findings are relevant for applications of polyelectrolyte microcapsules with encapsulated ion-sensitive dyes as biosensors.
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            Translational dynamics of photoexcited atoms in 4He nanodroplets: the case of silver.

            The dynamics following the photoexcitation of Ag atoms in (4)He nanodroplets via the 5p (2)P1/2 ← 5s (2)S1/2 and 5p (2)P3/2 ← 5s (2)S1/2 transitions has been investigated in a joint experimental and theoretical effort. It has been experimentally found that upon excitation to the (2)P1/2 state, the Ag atoms are ejected with a speed distribution peaking at about 55 m s(-1). When Ag is excited to the (2)P3/2 state, a rich phenomenology is found. While a fraction of the impurities remains solvated, the impurities that are ejected from the droplets either as Ag or AgHe have speed distributions similar, but not identical, to those found for excitation to the (2)P1/2 state. The experimental findings are qualitatively analyzed within a three-dimensional, time-dependent density functional approach for the helium droplet. The dynamics of the Ag-(4)He1000 system has been followed for several tens of picoseconds, long enough to observe AgHe exciplex formation and the departure of the photoexcited Ag atom from the helium droplet.
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              J. Appl. Electrochem.

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                Author and article information

                Contributors
                Role: ND
                Role: ND
                Role: ND
                Role: ND
                Journal
                jbchs
                Journal of the Brazilian Chemical Society
                J. Braz. Chem. Soc.
                Sociedade Brasileira de Química (São Paulo )
                1678-4790
                August 2002
                : 13
                : 4
                : 516-521
                Affiliations
                [1 ] Comissão Nacional de Energia Nuclear Brazil
                Article
                S0103-50532002000400017
                10.1590/S0103-50532002000400017
                5673df6f-4139-48e0-801d-a18a05a298e4

                http://creativecommons.org/licenses/by/4.0/

                History
                Product

                SciELO Brazil

                Self URI (journal page): http://www.scielo.br/scielo.php?script=sci_serial&pid=0103-5053&lng=en
                Categories
                CHEMISTRY, MULTIDISCIPLINARY

                General chemistry
                electrocatalyst,fuel cell,methanol oxidation,reformate gas
                General chemistry
                electrocatalyst, fuel cell, methanol oxidation, reformate gas

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