Atomistic Modeling of Corrosion Resistance: A First Principles Study of O2 Reduction on the Al(111) Surface Covered with a Thin Hydroxylated Alumina Film. Issue 3 (19th March 2014)

• Record Type: Journal Article
• Authors: Costa, Dominique; Ribeiro, Thomas; Mercuri, Francesco; Pacchioni, Gianfranco; Marcus, Philippe
• Is Part Of: Advanced materials interfaces. Volume 1:Issue 3(2014)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2014-03-19
• Subjects: Materials science -- Periodicals; 620.11
• DOI: 10.1002/admi.201300072
• Languages: English
• ISSNs: 2196-7350

Abstract

<abstract abstract-type="main" xml:lang="en"> <title> <x xml:space="preserve">Abstract</x> </title> <p>In the early stage of corrosion of Al or Al alloys (i.e., during the initiation of localized corrosion), an oxide film is generally present on the surface. This work investigates the possibility for a cathodic reaction to occur on these oxide films. We discuss realistic models of supported oxide films on Al(111) in order to disentangle the factors determining the reactivity towards O<sub>2</sub>. Three components of the complex film formed on Al(111) can be identified: an ultrathin under‐stoichiometric Al<sub>x</sub>O<sub>y</sub> interface layer, an intermediate Al<sub>2</sub>O<sub>3</sub> phase with γ‐alumina structure, and an hydroxylated AlOOH surface termination with boehmite structure. The electron transfer to O<sub>2</sub> molecules depends on the workfunction, Φe, of the metal/oxide interface and on the thickness of the inner Al<sub>2</sub>O<sub>3</sub> phase. The electron transfer takes place both from the metal‐oxide interface and the oxide surface to the adsorbed O<sub>2</sub> molecule. Very important is the role of the hydroxyl groups at the surface: they eliminate the Al surface states and stabilize the surface; they allow the reduced O<sub>2</sub><sup>−</sup> species to capture protons and transform into hydrogen peroxide in a non‐activated process. H<sub>2</sub>O<sub>2</sub> is further reduced to two water molecules, in a series of two‐electron mechanisms. These reactions take place only when the internal alumina phase is ultrathin (here 0.2 nm). As soon as an Al<sub>2</sub>O<sub>3</sub> inner layer develops (film thickness of about 1 nm), the film becomes unreactive and passivates the Al(111) surface. The results help to shed light on the complex reactions responsible for metal corrosion.</p> </abstract>