Electron Density Topological Analysis of Adsorbates on Pt and Pt Alloy Fuel Cell Catalytic Layers

Abstract

Phenomenological models based on adsorbate orbital occupation have shortcomings. Orbital charges, obtained by integration of densities-of-states (DOS) spectra, do not always correlate to bond strengths. Bader and co-workers have developed the quantum theory of atoms in molecules (QTAIM), which is based on the topology of electron densities, gradients and Laplacians of those densities to describe atoms and bonds of chemical systems. The advantage of QTAIM analyses is that they are basis set and method independent, as long as a minimally adequate basis set is used. We apply both QTAIM and adsorbate orbital approaches to the study of co-adsorption of water and carbon monoxide on Pt and Pt alloy catalytic surfaces relevant to polymer electrolyte fuel cell anodes, and show how the use of both approaches are complementary.