Pt–Ru-supported electrodes deposited by multiple successive cycles of potentiostatic pulses: evaluation of Nafion film effect on methanol oxidation

The influence of thin Nafion films on electrodeposited Pt–Ru electrocatalysts for the electro-oxidation of methanol was studied. Nanostructured planar carbon-supported Pt–Ru electrodes, on which a layer of Nafion ionomer was incorporated, were prepared by multiple cycles of potentiostatic pulses. SEM and AFM images of the deposit showed Pt–Ru particles grouped in agglomerates with sizes between 50 and 200 nm constituted by small nano-sized crystallites. The activity of the electrodes was found to decrease when the thickness of the Nafion film was increased, but the Tafel slope value was found to remain almost unchanged in all electrodes. These results may be associated with the partial blocking of the surface active sites by hydrophobic domains of the polymer, and the presence of CO2 molecules retained within the Nafion hydrophilic microchannels.