Theoretical Analysis of Electrochemical Formation and Phase Transition of Oxygenated Adsorbates on Pt(111)

详细信息    查看全文

• 作者：Junxiang Chen ; Siwei Luo ; Yuwen Liu ; Shengli Chen
• 刊名：ACS Applied Materials & Interfaces
• 出版年：2016
• 出版时间：August 10, 2016
• 年：2016
• 卷：8
• 期：31
• 页码：20448-20458
• 全文大小：599K
• 年卷期：0
• ISSN：1944-8252

文摘

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.