Abstract

The electrochemical interface formed by semiconducting metal oxide electrodes (TiO2, Fe2O3) is still a major challenge for modelling. The oxide surface can adsorb (or release) protons as ions similar to main group oxides (SiO2, Al2O3). However, the protons can also be partially or fully discharged by electrons in the solid as happens at metallic electrodes (proton coupled electron transfer). The work in my group over the past ten years has resulted in the development of a density functional theory based molecular dynamics (DFTMD) method for computing the “intrinsic” equilibrium constants for this process (acidities, ionization and dehydrogenation free energies). However, these are not the only parameters needed to describe the interface. Oxide surfaces can carry net charge. For semiconductors this will induce not one, but two double layers, one on the electrolyte side (a Helmholtz layer at high ionic strength) and one at the electrode side, a space charge layer (depletion layer for n-type semiconductors). After a summary of our DFTMD method, we try to outline in this talk how we think (or rather hope) the equilibrium constants computed by the DFTMD simulation can be used in an analytic model for an “electron coupled proton adsorption isotherm”. Such a DFTMD parametrized isotherm should enable us to analyse the effect of double layers on the (photo)electrocatalytic properties of the metal oxide as will be shown for the example of the oxidation of adsorbed water molecules.