Elen Leal da Silva

Platinum-Free Catalysts for Alkaline Polymer Electrolyte Fuel Cells

Platinum is known as the best catalyst for fuel cells reactions, because it presents the best catalytic activity and stability, mainly in acidic media. However, due to the high cost of platinum and its lower availability, the development of platinum-free catalysts for Alkaline Polymer Electrolyte Fuel Cells has been proposed. This work aims to compare catalysts characteristics obtained from two different synthesis methods. Ni catalysts were obtained by the impregnation/reduction method and by electroless deposition. The morphology of the electro-catalysts obtained were characterized by SEM-EDS and the electrochemical behavior was evaluated by Cyclic Voltammetry. And the composition of the catalysts obtained by the impregnation/reduction method was analyzed by Rutherford Backscattering Spectroscopy. The results obtained showed that the catalyst elaborated by the impregnation/reduction method developed higher current densities values than the catalyst elaborated by electroless deposition.

Catalyst based on Pt, Sn and Ni: Effect of carbon functionalization on ethanol electro-oxidation

Composite nanocatalysts, based on platinum, tin and nickel on carbon, using mono, binary and ternary systems, for the electro-oxidation of ethanol in direct ethanol fuel cells were synthesized in this work. The effect of carbon pre-treatment in HNO3 solution on the electro-oxidation of ethanol was characterized by cyclic voltammetry and electrochemical impedance spectroscopy. The results showed that the nanoparticles containing only platinum and the ones containing platinum and tin supported on functionalized carbon presented higher electrocatalytic activities for ethanol oxidation, compared to the ones supported on the non-functionalized carbon. The presence of tin and nickel in the platinum system (binary and ternary systems) promoted the catalytic activity in both ends, the oxidation of ethanol and the oxidation of intermediate carbon species.

The Behavior of Galvanized Steel Coated with a Double and Triple Layer of Hybrid Films

The aim of this work is to characterize by electrochemical, physicochemical and morphological analysis the hybrid films applied on galvanized steel by dip-coating process. Preliminaries studies showed that a monolayer of silane is not enough to increase the corrosion resistance protection of the substrate. In this context, the galvanized steel was coated with a double and triple layer of hybrid film obtained from a sol constituted by silane precursors 3 - (trimetoxisililpropil) methacrylate (TMSPMA) and tetraethoxysilane (TEOS) with addition of cerium nitrate at a concentration of 0.01M. The hybrid films were cured for 20 minutes at 60°C in each application of the film. The results showed that a double and triple layer of hybrid film increase the barrier effect contributing to corrosion protection of galvanized steel.

GALVANIZED STEEL PRE-TREATED WITH HYBRID FILM CURED BY UV: INFLUENCE OF PHOTOINITIATOR CONCENTRATION ON THE CORROSION RESISTANCE

Several coatings have been proposed as an alternative to replacement processes based on hexavalent chromium. Among them stand out the hybrid films. Some hybrids films, with modified composition by the addition of photoinitiators, can be cured by ultraviolet system (UV). The UV cure is the instantaneous conversion of a reactive liquid in a solid induced by radiation, starting from the polymerization and cross-linking reactions of the chemical species. In order that reaction takes place through the action of UV radiation, it is necessary to add, in the composition of the hybrid film, a substance sensitive to this radiation called photoinitiator. The aim of this work is the preparation and characterization of hybrid films, cured by UV, from TEOS and TMSPMA alkoxide precursors, with addition of photoinitiators with different concentrations (1 and 2%) and without photoinitiator on galvanized steel. The films were characterized concerning the morphology, physicochemical properties and electrochemical behavior. The presence and the increase of photoinitiator concentration on hybrid films improved corrosion resistance of the system.

Tratamiento Superficial de Acero Galvanizado con Películas Híbridas formadas por 3-(trimetoxisililpropil) metacrilato (TMSPMA) y Tetraetoxisilano (TEOS)

Acero galvanizado fue revestido con una pelicula hibrida a partir de una solucion formada por los precursores silanos 3-(trimetoxisililpropil) metacrilato (TMSPMA) y tetraetoxisilano (TEOS) con adicion de cerio. El uso de capas hibridas organico-inorganico representa una alternativa ambientalmente aceptable para mejorar la resistencia de una serie de materiales metalicos frente a los procesos corrosivos. Se emplearon tres tiempos de inmersion (2, 10 y 15 minutos) y se caracterizaron las peliculas mediante microscopia electronica de barrido, evaluando tambien el caracter hidrofobico de las peliculas. El comportamiento electroquimico de los revestimientos obtenidos fue determinado por el monitoreo del potencial de circuito abierto, polarizacion potenciodinamica e impedancia electroquimica. Los resultados que se obtuvo evidenciaron el efecto del tiempo de permanencia dentro de la solucion en la uniformidad de la pelicula y consecuentemente sobre la resistencia a la corrosion del mismo.