The Role of Ferromagnetic Substrate in the Reactivity of Pt/Fe Overlayer: A Density Functional Theory Study

We investigated the energetics of O-2 reaction on a model bimetallic system, Pt bilayer on Fe(001), using six-dimensional potential-energy surface derived from spin-polarized density functional theory calculations. The model system renders same surface geometry and binding energy with the reference system, unresconstructed Pt(001), thus a systematic investigation on the role of Fe substrate was appropriately conducted. Results show that O-2 dissociation may proceed from a "no barrier" molecular adsorption on bridge with O-O axis lying parallel to the surface and spanning towards top sites (t-b-t) to translation towards four-fold hollow site (b-h-b) yielding dissociated O atoms on the bridge. In this reaction pathway, O-2 should overcome an activation barrier of similar to 0.15 eV with respect to the initial state, which is comparable to that of the reference system (similar to 0.14 eV). However, the binding energy of O-2 with respect to its gas phase in all three states (initial, transition and final) is less as compared to that of Pt(001). The close relationship between adsorption energies and activation barriers with the spin polarization of Pt d-states near the Fermi-level induced by the ferromagnetic Fe substrate is discussed.