60th Annual Report on Research 2015

The development of new nanoscale materials has led to exciting possibilities in heterogeneous catalysis, but also leads to fundamental questions concerning the connection between surface functionalization and reactivity. One of the fundamental complications in predicting the reactivity of catalytically active nanoparticles is understanding the influence of surface ligands, which are frequently necessary in colloidal synthesis methods.

The first aim of the project has been a systematic study on the effects of ligand binding strength and structure on the activity of platinum nanoparticles towards electrocatalytic methanol oxidation. Recent publications in this area have demonstrated that the topic is of broad interest, but results in our lab and in other reports have revealed limitations to the fundamental research in this topic. Specifically, it has been difficult to separate the effects of surface ligands from their effect on nanoparticle size because of the sensitivity of nanoparticles to molecules in the synthesis mixture or to subsequent functionalization steps. As a result, we have broadened our approach to consider the impact of amine and thiol-based ligands on electrocatalytic activity of planar platinum surfaces, where we can ensure a consistent surface area and crystallinity.

We have found that thiol molecules bind quickly to the platinum surface and substantially decrease electrocatalytic activity. However, amines, which are commonly used in nanoparticle synthesis, have a much more limited effect on activity. We have quantified the effects of straight chain alkyl-amines on electrocatalytic activity as a function of surface coverage and investigated the molecular ordering and density of ligands on the surface. We are currently beginning to study the effects of ring-based structures, including aromatic and non-aromatic systems to systematically control the amount of steric hindrance in the systems.

Two undergraduate students have worked on this project in the past year, including full-time summer employment funded by this grant and continuing work during the current academic year. They have both been trained in the analytical techniques in my laboratory and have been trained in scanning electron microscopy, including use of facilities at the Harvard Center for Nanoscale Systems, which gives them exposure to state of the art facilities not available at our liberal arts college.