(621y) Structures, Dynamics & Catalytic Performance of Platinum Surface Oxides

Platinum has numerous technological applications in environments, in which oxygen is readily available to adsorb on or oxidize its surface (e.g. in polymer electrolyte fuel cells [1] and in catalytic converters in automobiles [2]). To understand the influence of this adsorbed oxygen or surface oxide on platinum’s catalytic behavior, the composition and structure of platinum surfaces in operando need to be determined. In this regard, important questions related to the oxygen adsorption and surface oxide formation remain unanswered, even in the case of the thermodynamically most stable and most widely studied Pt(111) surface.

To address these questions we have parameterized a ReaxFF reactive force field [3] for Pt/O and applied it to study the thermodynamics and kinetics of Pt(111) oxidation. For oxygen coverages up to one atomic monolayer on Pt(111) surface energy calculations for hundreds of ordered potential surface structures reveal four regimes of thermodynamically stable surface configurations, which are characterized by pure adsorption, high and low coverage buckled structures, and subsurface oxygen, respectively. These structures and simulated temperature programmed desorption (TPD) spectra, exclusively obtained from first principles data, compare favorably with and complement published scanning tunneling microscopy (STM) and TPD experiments [4].

To investigate structures with oxygen coverages exceeding one monolayer grand canonical Monte Carlo simulations were employed in a search for stable (or metastable) amorphous surface oxide structures. The structures identified using this procedure and the conditions (temperature and pressure) under which they are expected to exist explain recent experimental results, and provide additional insight into the roles that surface buckling and subsurface oxygen play in the surface oxidation process. These surface-oxide and surface-oxide-precursor structures are expected to strongly impact the (electro)catalytic properties of partially oxidized Pt(111) surfaces.

[1] Adžić, R., Electrocatalysis, Ed. J. Lipkowski, P. Ross, Wiley-VCH, 1998, 197–242.

[2] Engel T.; Ertl, G., Advances in Catalysis, Ed. H. P. D.D. Eley,  P. B. Weez, Academic Press, 1979, 1–78.

[3] Fantauzzi, D.; Bandlow, J.; Sabo, L.; Mueller, J.E.; van Duin, A. C. T.; Jacob, T.
Phys. Chem. Chem. Phys., 16, 2014, 23118–23133.

[4] S. P. Devarajan, J. A. Hinojosa Jr., J. F. Weaver, Surf. Sci., 602, 2008, 3116–3124.