Roles of Proton and Electric Field in the Electroreduction of O2 on Pt(111) Surfaces: Results of an Ab-Initio Molecular Dynamics Study
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abstract
The electroreduction of O 2 on the Pt(1 1 1) surface is studied with Car-Parrinello molecular dynamics simulations of O 2/Pt(1 1 1), O 2 + H +(H 2O) 3/Pt(1 1 1), and O 2 + H +(H 2O) 3 + e -/ Pt(1 1 1). Starting from a parallel configuration where O 2 is 3.0 over the Pt(1 1 1) surface along a bridge site, stepwise adsorptions of two oxygen atoms are observed, leading to a one-end chemisorption precursor (Pauling model of adsorption). The formation of the precursor has a very low barrier (0.08 eV), whereas no clear barrier was found for its decomposition. Addition of H +(H 2O) 3 induces rapid formation of the proton-transfer intermediate H +-O 2/Pt(1 1 1), followed by an electron transfer from the Pt slab that yields a chemisorbed precursor H-O-O-Pt n in which the hydroxyl end is considerably more separated than the oxygen end from the Pt(1 1 1) surface. Compared with the O 2 + H +(H 2O) 3/Pt(1 1 1) system, the presence of an electron in 02 + H(H 2O) 3 + e/Pt(1 1 1) greatly enhances the lifetime of the proton-transfer intermediate H-O-O...Pt(1 1 1), and consequently it delays the subsequent electron transfer, which yields the formation of the one-end chemisorbed precursor H-O-O-Pt n. Evolutions of the Kohn-Sham energy for the last two cases show that the formation of H-O-O-Pt n has a much higher activation barrier than its dissociation (0.4 vs 0.1 eV), indicating that the formation of chemisorbed H-O 2 species is the rate-determining step for the first electron transfer of the electroreduction of O 2.
