  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.
