title: Theoretical Analysis of Electrochemical Formation and Phase Transition of Oxygenated Adsorbates on Pt(111).
abstract: The electrochemical oxygenation processes of Pt(111) surface are investigated by combining density functional theory (DFT) calculations and Monto Carlo (MC) simulations. DFT calculations are performed to construct force-field parameters for computing the energy of (√3 × √3)R30°-structured OH*-H2O* hydrogen-bonding networks (differently dissociated water bilayer) on the Pt(111) surface, with which MC simulations are conducted to probe the reversible H2O* ↔ OH* conversion in OH*-H2O* networks. The simulated isotherm (relation between electrode potential and OH* coverage) agrees well with that predicted by the experimental cyclic voltammetry (CV) in the potential region of 0.55-0.85 V (vs RHE). It is suggested that the butterfly shape of CV in this region is due to different variation trends of Pt-H2O* distance in low and high OH* coverages. DFT calculation results indicate that the oxidative voltammetry in the potential region from 0.85 V to ca. 1.07 V is associated with the dissociation of OH* to O*, which yields surface structures consisting of OH*-H2O* networks and (√3 × √3)-structured O* clusters. The high stability of the half-dissociated water bilayer (OH*-H2O* hydrogen-bonding network with equal OH* and H2O* coverages) formed in the butterfly region makes OH* dissociation initially very difficult in energetics, but become facile once starts due to the destabilization of OH* by the formed O* nearby. This explains the experimentally observed nucleation and growth behavior of O* phase formation and the high asymmetry of oxidation-reduction voltammetry in this potential region.
authors.affiliation: Hubei Key Laboratory of Electrochemical Power Sources, Key Laboratory of Analytical Chemistry for Biology and Medicine (Ministry of Education), Department of Chemistry, Wuhan University , Wuhan 430072, China.
authors.forename: Junxiang
authors.initials: J
authors.lastname: Chen
authors.affiliation: Hubei Key Laboratory of Electrochemical Power Sources, Key Laboratory of Analytical Chemistry for Biology and Medicine (Ministry of Education), Department of Chemistry, Wuhan University , Wuhan 430072, China.
authors.forename: Siwei
authors.initials: S
authors.lastname: Luo
authors.affiliation: Hubei Key Laboratory of Electrochemical Power Sources, Key Laboratory of Analytical Chemistry for Biology and Medicine (Ministry of Education), Department of Chemistry, Wuhan University , Wuhan 430072, China.
authors.forename: Yuwen
authors.initials: Y
authors.lastname: Liu
authors.affiliation: Hubei Key Laboratory of Electrochemical Power Sources, Key Laboratory of Analytical Chemistry for Biology and Medicine (Ministry of Education), Department of Chemistry, Wuhan University , Wuhan 430072, China.
authors.forename: Shengli
authors.initials: S
authors.lastname: Chen
keywords: Monto Carlo simulations; Pt(111); density functional theory; nucleation and growth; oxygenated adsorbates; phase transition