Spin-polarized density functional theory study of reactivity of diatomic molecule on bimetallic system: the case of O2 dissociative adsorption on Pt monolayer on Fe(001).

The energetics of O(2) adsorption and dissociation are discussed in terms of 6D potential energy surface based on spin-polarized density functional theory calculations that predict O(2) access to both molecular and dissociative chemisorption wells with no obvious barriers. Specifically, a molecularly chemisorbed state in a top-bridge-top (t-b-t) configuration is identified, and a "no barrier" dissociative adsorption over hollow site with the O-O axis spanning toward the bridge sites (b-h-b) is noted. Both the translation of O(2) from the molecular state (t-b-t) to the dissociated state on bridge and the direct nonactivated dissociative adsorption over the hollow sites (b-h-b) are likely pathways for O(2) dissociation. Interestingly, such O(2) reaction pathways are consistent with the density functional theory calculations and molecular beam experiments on O(2) dissociative adsorption on Pt(100)-(1 x 1). Modification of the electronic structure of the Pt surface due to the Fe substrate relevant for O(2) reactivity is discussed in an effort to provide insight into the experimentally discovered significant enhancement in electrocatalytic activity of Pt-Fe alloys for fuel cell applications.