Abstract
Despite the growing interest in Mg and its alloys, their use has been largely limited due to their high reactivity in aqueous environments. Improving the understanding of the basic principles of Mg corrosion represents the first step to explain and, eventually, improve the corrosion behaviour of Mg alloys. Herein an original mechanistic surface kinetic DFT model that clarifies the mechanism of anomalous HE on anodically polarised Mg is presented. In accordance with several experimental observations, this model describes anomalous HE proceeding at the regions dominated by anodic dissolution via the reaction of an Mg*H intermediate with water. The Mg*H intermediates undergo oxidation upon anodic polarisation, resulting in hydrogen evolution and Mg dissolution. Furthermore, it is revealed that increasing rates of an electrochemical cathodic reaction are possible within a dissolving anode.
Highlights
When magnesium (Mg) is exposed to water, corrosion occurs with hydrogen evolution as the primary cathodic reaction
We present an original mechanistic surface kinetic density functional theory (DFT) model that clarifies the mechanism of anomalous HE on anodically polarised Mg
The mechanism proposed is composed of competing reactions that simultaneously occur at the interface between the Mg surface and the aqueous electrolyte
Summary
When magnesium (Mg) is exposed to water, corrosion occurs with hydrogen evolution (from the reduction of water) as the primary cathodic reaction. In aqueous environments, Mg exhibits the opposite behaviour with the rate of the hydrogen evolution reaction (HER) increasing with increasing anodic polarisation above the open circuit potential [2], which contradicts expectations of standard electrochemical kinetics. This behaviour, which we refer to as anomalous HE has been observed for a long time [3], but its reaction mechanism is unknown and remains a topic of intense investigation. We present an original mechanistic surface kinetic DFT model that clarifies the mechanism of anomalous HE on anodically polarised Mg. it is revealed that increasing rates of an electrochemical cathodic reaction are possible within a dissolving anode
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