Structure and Architecture Driven Metallic Bonding and Ligand Effects in Low-Dimensional Platinum Group Metal Catalyst

Abstract

Whether grown as clusters or ultrathin films, extremely small quantities of active elements exhibit changes in catalytic activity that arise from both size effects and electron-transfer effects. These size and transfer effects can be related to increased propensity for oxidation of the metallic deposit, as well as to various changes in electrochemical performance such as durability or required overpotential for a given reaction. A review of our recent work on layer-by-layer near-surface effects of atomic and electronic structure on catalytically relevant properties will be presented. We use electrochemical atomic layer deposition for layer-by-layer growth of platinum group metals (PGM), and measure the evolution of electronic and atomic structure using synchrotron-based X-ray Photoelectron Spectroscopy (XPS) and X-ray absorption spectroscopy. XPS using a tunable energy synchrotron X-ray source allows us to profile the transitions in the electronic structure from the surface down to the adlayer/support interface and beyond. In addition to depth profile studies of these layered metal architectures, the effects of thermally and electrochemically activated near-surface alloying in the PMG systems will be presented here. We observe undulations of near-surface electronic structure brought on by the low dimensionality of the PMG adlayer as well as the adlayer-support interactions, effects that can explain the resulting surface.