Inhibition of water dissociation on a pitted Pt(1 1 1) surface: First principles study

First principles molecular dynamics has been used to simulate the interface between a defective Pt surface that contains a pit with coadsorbed OH and liquid water under a bias. Water dissociation was not observed even under a strong bias (corresponding to a Pt surface charge of σ = 14 μC/cm2) although it was observed on a flat surface with less surface charge. The OHad is located at a top site of the flat surface but it is at a bridge site of the pitted surface. Surface morphology and hydrogen bonding, therefore, have a significant impact on water dissociation. The OHad promotes water dissociation on the flat surface because it makes a hydrogen bond with a water molecule adsorbed on the Pt top site; however, on the pitted surface, water dissociation is prohibited because of an unfavorable formation of a hydrogen bond between the OHad on the bridge site and the H2O on the top site. Our electronic structure calculation shows an unsymmetrical electron distribution between the two OH bonds of the water molecule, in which the OH bond with fewer electrons (opposite side of the hydrogen bond with OHad) is dissociated to produce H3O+ with another water molecule.

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► First principle molecular dynamics simulations show water split on flat Pt surface.
► Not split on pitted surface is observed even with large amount of charge added.
► OH adsorbs on top(bridge) site of flat(pitted) surface, water on top site of both surfaces.
► Hydrogen bonds between OHad and water exist on flat surface, but lack on pitted surface.
► OHad makes water polarized on flat surface, but has no effect on pitted surface.