Tuning the activity of platinum electrocatalysts via size, shape and capping polymer

The high cost and the low catalytic activity of the present anode catalysts are two major obstacles in the development of direct-methanol fuel cells (DMFCs). Platinum (Pt)-based catalysts are currently considered the best anode catalysts for methanol electro-oxidation reaction and their catalytic activity is highly dependent on their surface structure. During the past decade, several investigations regarding the electro-catalysis of methanol oxidation at nanoscale have been conducted. However, only a handful of these investigations were systematic approaches to correlate the catalytic activity of the Pt to the surface structure of the nanocatalysts. The shape and size of the nanoparticles are the major determinants of their surface structure. Therefore, the primary goal of this project is to investigate, in detail, the methanol electro-oxidation reaction on Pt nanoparticles of controlled shapes and sizes.;This thesis begins by introducing the surface orientation dependent electro-catalytic activities of Pt nanoparticles of controlled shapes and a mechanistic investigation detailing the intermediate species generated during methanol electro-oxidation reaction on these particles. Simple synthetic procedures for concomitant control of the shape and size of the Pt nanoparticles and the size dependency of the electro-catalytic activity for a defined shape will then be described. Subsequently, the enhanced electro-catalytic activity and stability of Pt nanoparticles with a dominant presence of (111) surface planes will be illustrated.;In electro-catalysis, it has always been assumed that the presence of a capping polymer would block the activity. Here is given the first evidence on the enhancing effect of the capping polymer polyvinylpyrrolidone (PVP) on the activity of Pt nanocatalysts for several electrochemical reactions. Additionally, in this thesis, the synthesis of ruthenium decorated Pt nanoparticles of defined shapes and the preliminary results on sulfur poisoning on Pt nanoparticles with a dominant presence of (111) surface planes will be described.;Overall, this project brings a new approach to fuel-cell related electro-catalysis research by demonstrating the tunability of the activity of Pt electro-catalysts through shape, size and capping polymer.