Coverage dependence and hydroperoxyl-mediated pathway of catalytic water formation on Pt (111) surface

Hydrogen oxidation on Pt (111) surface is modeled by density functional theory (DFT). Previous DFT calculations showed too large O ₂ dissociation barriers, but we find them highly coverage dependent: when the coverage is low, dissociation barriers close to experimental values (∼0.3 eV) are obtained. For the whole reaction, a new pathway involving hydroperoxyl (OOH) intermediate is found, with the highest reaction barrier of only ∼0.4 eV. This may explain the experimental observation of catalytic water formation on Pt (111) surface above the H ₂O desorption temperature of 170 K, despite that the direct reaction between chemisorbed O and H atoms is a highly activated process with barrier ∼ 1 eV as previous calculations showed.