As a promising alkaline earth metal with significant potential across various industrial applications, magnesium (Mg) and its alloys are appealing due to their impressive lightweight nature among all engineering metals. Nevertheless, inadequate aqueous corrosion resistance has noticeably hindered the broader applications of Mg alloys. Despite several experimental observations and theoretical investigations providing a primary understanding of the underlying mechanism of Mg aqueous corrosion, some anomalous corrosion behaviour of Mg under voltage bias, i.e., the negative difference effect (NDE) still eludes a comprehensive explanation. A detailed understanding of the electrified double-layer structure for Mg at the atomic scale, coupled with an in-depth knowledge of the thermodynamics and kinetics of corrosion reactions, is essential for unravelling the intrinsic mechanism of Mg aqueous corrosion.
Herein, first-principles simulations within the density functional theory (DFT) framework are employed to explore the electrochemistry and the atypical hydrogen evolution behaviour in Mg aqueous corrosion. To comprehend the basis of the Mg corrosion mechanism, the structure and the potential of zero charge (PZC) of the Mg/water interface are modelled using the ab initio molecular dynamics. The hydrogen adsorption process and the formation of hydride corrosion products that are assumed to contribute to the anodic hydrogen evolution reaction are investigated and found to be intricately regulated by electron localisation at the metal surface. To disclose the significance of sub-surface hydride in the NDE or other pivotal aspects of Mg aqueous corrosion electrochemistry, a thermodynamic study involving the construction of a surface Pourbaix diagram, with a kinetic investigation entailing the calculation of reaction energy barriers under various surface conditions, is presented in this thesis. This research contributes novel perspectives to the ongoing debate about the NDE during Mg aqueous corrosion and provides rational theoretical evidence derived from the ab initio simulations.