How low can you go? Minimum energy pathways for O2 dissociation on Pt(111)

Many DFT studies of O(2) dissociation on Pt(111) give conflicting information on preferred paths and final states. Here we report large p(4 × 4) unit cell minimum energy pathway evaluations and compare O(2) adsorption and dissociated states on Pt(111). Calculations reveal how the pathways for O(2) dissociation starting from top-fcc-bridge, top-hcp-bridge, and top-bridge-top sites are interconnected. They also provide a direct reaction pathway for the dissociation of an O(2) molecule from a top-fcc-bridge into an hcp and an fcc site, which is consistent with low temperature scanning tunneling microscope experiments. Such a pathway is shown to be considerably perturbed by the presence of co-adsorbed oxygen atoms. We quantify the coverage dependence through the construction of a Brønsted-Evans-Polanyi relationship relating the O(2) dissociation activation energies to the binding energies of the dissociated O atoms. We also show that all pathways starting from a top-fcc-bridge site give the smallest barriers for O(2) dissociation.