Parameterization and Extension of a Model of Oxide Growth by a Multi-Method Approach

Abstract

The technology to form anodic oxides on valve metals will strongly benefit from optimization of process parameters based on deterministic modelling. The relatively large number of adjustable parameters precludes the unambiguous interpretation of steady-state and transient electrochemical data in terms of a unique kinetic model. An approach to overcome this challenge by parameterization of a model of film growth and dissolution using a combination of in situ electrochemical impedance spectroscopy (EIS) in a large frequency range, dynamic high-frequency impedance and photocurrent measurements, with ex situ characterization of the oxides by X-ray photoelectron spectroscopy (XPS) is presented. Additional mechanistic information is derived from density functional theory modelling of adsorption of water and fluoride on TiO2. An extension of the model allowing for a multistep transpassive dissolution reaction at the film/solution interface is also parameterized using voltametric, EIS and XPS data for the anodic oxidation of Mo in concentrated H3PO4.