Regensburg 2007 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 67: Symposium: The Solid-Liquid Interface: A Challenge for Theoreticians II
O 67.7: Vortrag
Freitag, 30. März 2007, 12:15–12:30, H38
Theoretical Studies on the Electro-Oxidation of Pt-electrodes — •Timo Jacob and Matthias Scheffler — Fritz-Haber-Institut der MPG, D-14195 Berlin, Germany
Using an extension of the ab initio atomistic thermodynamics approach to electrochemical systems the interfacial structure and composition of Pt-electrodes in aqueous electrochemical environments was studied. Focusing on positive electrode potentials, at which first electro-oxidation and then oxide-formation occurs, we evaluated the full (p,T,φ)-surface phase diagram. Assuming experimental temperature and pressure conditions, we find that after forming a (2×2) structure at 0.95 V, the bulk-oxide is thermodynamically stable above 1.20 V. Consequently, the assumption of a plain Pt-electrode, often used in the modeling of electrochemistry, is clearly incomplete. Instead, the surface structure and composition is significantly modified. To further investigate the oxide-formation, we focused on bulk-oxide systems and calculated the stability of the low-index surfaces of α-PtO2, β-PtO2, and PtO bulk-oxides. On the basis of formation energies we first deduced the stability ranges at which the bulk-oxides are the thermodynamically stable phase. Afterwards for each of the considered bulk-oxides the corresponding (p,T,φ)-phase diagram of surface structures was obtained, showing a preference for α-PtO2(001), β-PtO2(110), and PtO(100) respectively, which all have PtO2 bulk-like compositions even on their surfaces. However, in case of thin oxide layers a PtO composition might also be relevant.