The thermodynamically favored reaction between water and magnesium, Mg + 2H2O → Mg(OH)2 + H2, is
normally sluggish, but it becomes reasonably rapid when a milled composite of powdered magnesium metal
and powdered iron (1−10 mol %) is used with sodium chloride solutions. Iron functions as an activator, and
chloride functions as a catalyst that depassivates the outermost oxide/hydroxide layer and allows water to
penetrate to the activated magnesium surface. Adding solutes such as sodium nitrate, copper(II) chloride, and
sodium trichloroacetate to the reaction mixture suppresses the yield of dihydrogen. Manometric and calorimetric
studies on the stoichiometry and kinetics of the reaction between Mg(Fe) powders and aqueous solutions
demonstrate that short-lived, partially, and fully solvated electrons (
and
) are precursors of dihydrogen
and that they and the hydrogen atoms (H•) formed from them can be scavenged, resulting in suppressed
dihydrogen yields.
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