On the origin of univalent Mg$^+$ ions in solution and their role in anomalous anodic hydrogen evolution

TL;DR

This study uncovers the formation of univalent Mg$^+$ ions during magnesium corrosion, challenging traditional assumptions and providing new insights into the mechanisms behind anomalous hydrogen evolution in aqueous solutions.

Contribution

The paper introduces a novel reaction pathway showing the formation of solvated Mg$^{2+}$(OH)$^-$ complex, explaining the presence of Mg$^+$ ions and impacting corrosion prevention strategies.

Findings

Formation of solvated Mg$^{2+}$(OH)$^-$ complex during dissolution

Unveiling of a reaction mechanism producing Mg$^+$ ions

Implications for corrosion prevention strategies

Abstract

Aqueous metal corrosion is a major economic concern in modern society. A phenomenon that has puzzled generations of scientists in this field is the so-called anomalous hydrogen evolution: the violent dissolution of magnesium under electron-rich (anodic) conditions, accompanied by strong hydrogen evolution, and a key mechanism hampering Mg technology. Experimental studies have indicated the presence of univalent Mg$^+$ in solution, but these findings have been largely ignored because they defy our common chemical understanding and evaded direct experimental observation. Using recent advances in the \emph{ab initio} description of solid-liquid electrochemical interfaces under controlled potential conditions, we described the full reaction path of Mg atom dissolution from a kinked Mg surface under anodic conditions. Our study reveals the formation of a solvated [Mg$^{2+}$(OH)$^-$]$^+$ ion complex, challenging the conventional assumption of Mg$^{2+}$ ion. This insight provides an intuitive explanation for the postulated presence of (coulombically) univalent Mg$^+$ ions and the absence of protective oxide/hydroxide layers normally formed under anodic/oxidizing conditions. The discovery of this unexpected and unconventional reaction mechanism is crucial for identifying new strategies for corrosion prevention and can be transferred to other metals.