Berlin 2015 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 25: Focus Session: Structure, Chemistry, and Ion Solvation at Solid-Liquid Interfaces II

O 25.4: Topical Talk

Dienstag, 17. März 2015, 15:30–16:00, HE 101

Modelling of electrical double layers at metal oxide electrodes — •Michiel Sprik¹ and Jun Cheng² — ¹Department of Chemistry, University of Cambridge, Cambridge UK — ²Department of Chemistry, University of Aberdeen, Aberdeen, UK

Oxide surfaces exchange protons with an aqueous electrolyte and can therefore carry a net proton charge. The adsorbed protons at low pH can be partially or fully discharged by conduction electrons or the deprotonated anionic groups at high pH by holes. The "intrinsic" equilibrium constants for this process (acidities, ionization and dehydrogenation free energies) can be computed for charge neutral surfaces. We have developed such a method using Density Functional Theory based Molecular Dynamics (DFTMD, for an application to rutile titania see Angew Chem Int Ed Engl (2014) 53, 12046). An electrode with net excess or deficit proton charge can be described in first approximation by a triple layer model consisting of the charged electrode surface, ionic counter charge on the electrolyte side (a Helmholtz layer at high ionic strength) and a space charge layer on the electrode side. After a summary of our DFTMD method, we will outline in this talk how the equilibrium constants computed by the DFTMD simulation can be used in an analytic model for an "electron coupled proton adsorption isotherm". The additional parameter in this model is the capacitance of the Helmholtz layer. Such a parametrized isotherm should enable us to analyse the effect of double layers on the (photo) electrocatalytic properties of metal oxides as will be shown for the example of the oxidation of adsorbed water molecules.