Nafion-stabilized Pt Nanoparticles and the Effect of Pt Distribution on the Electrochemical Reduction of Oxygen

Abstract

Nafion stabilized Pt sols was prepared by using methanol to reduce the precursor H2PtCl6. No other ingredient was used in the preparation and Pt nanoparticles of 2 -3 nm size were obtained. Platinum nanoparticles were found to form aggregates. The aggregate size and the stability of Pt sols could be changed by solvent treatment. This suggests that SO3¯ functional groups of Nafion stabilized Pt nanoparticles and that the aggregates formed due to the formation of ionic clusters of Nafion. The electrochemical reduction of oxygen was examined with carbon supported Nafion-Pt catalysts of different aggregate size. At low overpotential, the kinetic rate was not changed by the aggregate size. At high overpotential region where mass-transfer limitation phenomenon was observed, the reaction rate increased with decreasing aggregate size. It indicates that smaller aggregates, i.e., the more even Pt distribution, are less subjected to mass-transfer limitation and could consequently provide better electrode performance.