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      Eletrocatálise das reações de oxidação de hidrogênio e de redução de oxigênio Translated title: Electrocatalysis of the hydrogen oxidation and oxygen reduction reactions

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          Translated abstract

          This work discusses the electrocatalytic processes taking place in the polymer electrolyte fuel cell electrodes, specifically the hydrogen oxidation reaction (HOR) and the oxygen reduction reaction (ORR), because these are clear examples of electrochemical reactions favored by the use of electrocatalysts. Since the gaseous reactants are very little soluble in the electrolyte, the use of special electrodes, named gas diffusion electrodes, is required to promote easy and continuous access of reactant gases to the electrocatalytic sites. Besides this, other important aspects such as the use of spectroscopic techniques and of theoretical models to improve the knowledge of the electrocatalytic systems are shortly discussed.

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          Quim. Nova

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            A new approach to nucleation of cavitation bubbles at chemically modified surfaces.

            Cavitation at the solid surface normally begins with nucleation, in which defects or assembled molecules located at a liquid-solid interface act as nucleation centers and are actively involved in the evolution of cavitation bubbles. Here, we propose a simple approach to evaluate the behavior of cavitation bubbles formed under high intensity ultrasound (20 kHz, 51.3 W cm(-2)) at solid surfaces, based on sonication of patterned substrates with a small roughness (less than 3 nm) and controllable surface energy. A mixture of octadecylphosphonic acid (ODTA) and octadecanethiol (ODT) was stamped on the Si wafer coated with different thicknesses of an aluminium layer (20-500 nm). We investigated the growth mechanism of cavitation bubble nuclei and the evolution of individual pits (defects) formed under sonication on the modified surface. A new activation behavior as a function of Al thickness, sonication time, ultrasonic power and temperature is reported. In this process cooperativity is introduced, as initially formed pits further reduce the energy to form bubbles. Furthermore, cavitation on the patterns is a controllable process, where up to 40-50 min of sonication time only the hydrophobic areas are active nucleation sites. This study provides a convincing proof of our theoretical approach on nucleation.
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              Electrochim. Acta

              E Yeager (1984)
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                Author and article information

                Contributors
                Role: ND
                Role: ND
                Role: ND
                Journal
                qn
                Química Nova
                Quím. Nova
                Sociedade Brasileira de Química (São Paulo )
                1678-7064
                August 2005
                : 28
                : 4
                : 664-669
                Affiliations
                [1 ] Universidade de São Paulo Brazil
                Article
                S0100-40422005000400020
                10.1590/S0100-40422005000400020
                82fcc7f6-a592-4c91-9fef-13a11c3eac66

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

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                SciELO Brazil

                Self URI (journal page): http://www.scielo.br/scielo.php?script=sci_serial&pid=0100-4042&lng=en
                Categories
                CHEMISTRY, MULTIDISCIPLINARY

                General chemistry
                electrocatalysis,hydrogen oxidation reaction,oxygen reduction reaction
                General chemistry
                electrocatalysis, hydrogen oxidation reaction, oxygen reduction reaction

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