"Balance of Nanostructure and Bimetallic Interactions in Pt Model Fuel Cell Catalysts: In Situ XAS and DFT Study"

Daniel Friebel: Venkatasubramanian Viswanathan, Daniel J. Miller, Toyli Anniyev, Hirohito Ogasawara, Ask H. Larsen, Christopher P. O’Grady, Jens K. Nørskov, Anders Nilsson; Journal of the American Chemical Society, 05/22/12.

Additional Authors: Venkatasubramanian Viswanathan, Daniel J. Miller, Toyli Anniyev, Hirohito Ogasawara, Ask H. Larsen, Christopher P. O’Grady, Jens K. Nørskov, Anders Nilsson

Abstract:

ABSTRACT: We have studied the effect of nanostructuring
in Pt monolayer model electrocatalysts on a Rh(111) singlecrystal
substrate on the adsorption strength of chemisorbed
species. In situ high energy resolution fluorescence detection
X-ray absorption spectroscopy at the Pt L3 edge reveals
characteristic changes of the shape and intensity of the “whiteline”
due to chemisorption of atomic hydrogen (Had) at low
potentials and oxygen-containing species (O/OHad) at high
potentials. On a uniform, two-dimensional Pt monolayer
grown by Pt evaporation in ultrahigh vacuum, we observe a
significant destabilization of both Had and O/OHad due to strain and ligand effects induced by the underlying Rh(111) substrate.
When Pt is deposited via a wet-chemical route, by contrast, three-dimensional Pt islands are formed. In this case, strain and Rh
ligand effects are balanced with higher local thickness of the Pt islands as well as higher defect density, shifting H and OH
adsorption energies back toward pure Pt. Using density functional theory, we calculate O adsorption energies and corresponding
local ORR activities for fcc 3-fold hollow sites with various local geometries that are present in the three-dimensional Pt islands.