Electrochemical Deposition of Platinum Nanoparticles for Methanol Oxidation

M.M.E. DUARTE; S. PILLA; J.M. SIEBEN; C.E. MAYER

Village Rio das Pedras, Club Med, Rio de Janeiro, Brasil

Congreso; 2nd Mercosur Congress on Chemical Engineering, 4th Mercosur Congress on Process Systems Enginnering; 2005

Universidad Federal de Rio de Janiero

Electrochemical deposition of platinum on different carbon substrates was applied to obtainsupported nanoparticles to use as electrocatalysts for the oxidation of methanol in acid media. Particles with well defined morphology and size can be obtained by this technique controlling electrodeposition potential and time. Glassy carbon and graphite fibers of 9 μm diameter were used as substrates. Platinum particles were deposited from chloroplatinic acid solutions with platinum concentration between 2 and 5 mM. In some cases a Nafion® ionomer film was applied over the electrode surface. Conventional electrochemical techniques were used to characterize supported platinum surface status. The catalyst surface area was determined from hydrogen adsorption electrical charge. Scanning electron microscopy was used to measure particle size and evaluate the particle dispersion over the substrate. Particle size and catalyst mass were determined by platinum concentration, deposition potential and time. The application of short potential pulsesat -0.5 V (ECS) during times variables from 0.2 to 10 s favored a more uniform dispersion of the particles and a general reduction in particle size. From specific surface area measurements particle diameters between 10 and 20 nm were estimated when glassy carbon was used as support. Differences in size and morphology were observed when Pt was deposited on graphite fibers. Notwithstanding using similar conditions, the particles on fibers were bigger and tending to coalesce. This behavior was ascribed to the highly hydrophobic surface of the fibers. Electrochemical methanol oxidation was studied on platinum supported on glassy carbon. The Pt electrocatalytic activity expressed as current per Pt mass was found to depend on the metalparticle size, showing a decreasing activity when the catalyst diameter increase.