title: Reversible redox reaction and water configuration on a positively charged platinum surface: first principles molecular dynamics simulation.
abstract: The water dissociation reaction and water molecule configuration on a positively charged platinum (111) surface were investigated by means of first principles molecular dynamics under periodic boundary conditions. Water molecules on the Pt surface were mostly in the O-down orientation but some H-down structures were also found. OH(-) ion, generated by removing H from H(2)O in the bulk region, moved to the Pt surface, on which a positive charge is induced, by a Grotthuss-like proton-relay mechanism and adsorbed on it as OH(Pt). Hydrogen atom exchange between OH(Pt) and a near-by water molecule frequently occurred on the Pt surface and had a low activation energy of the same order as room temperature energy. When a positive charge (7 μC cm(-2)) was added to the Pt surface, H(3)O(+) and OH(Pt) were generated from 2H(2)O on the Pt. This may be coupled with an electron transfer to the Pt electrode [2H(2)O → H(3)O(+) + OH(Pt) + e(-)]. The opposite reaction was also observed on the same charged surface during a simulation of duration about 10 ps; it is a reversible redox reaction. When further positive charge (14 μC cm(-2)) was added, the reaction shifted to the right hand side completely. Thus, this one-electron transfer reaction, which is a part of the oxygen electrode reaction in fuel cells and water electrolysis, was confirmed to be a low activation energy process.
authors: Advanced Institute for Materials Research (WPI), Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan. ikeshoji@wpi-aimr.tohoku.ac.jp
authors: Tamio
authors: T
authors: Ikeshoji
authors: Minoru
authors: M
authors: Otani
authors: Ikutaro
authors: I
authors: Hamada
authors: Yasuharu
authors: Y
authors: Okamoto