<p>Dissolution of
redox-active metal oxides plays a key role in a variety of phenomena including
(photo)electrocatalysis, degradation of battery materials, corrosion of metal
oxides and biogeochemical cycling of metals in natural environments. Despite its
widespread significance, mechanisms of metal-oxide dissolution remain poorly understood
at the atomistic level. This study is aimed at elucidating the long-standing problem
of iron dissolution from Fe(III)-oxide, a complex process involving coupled hydrolysis,
surface protonation, electron transfer, and metal-oxygen bond cleavage. We examine
the case of goethite (α-FeOOH), a representative phase bearing structural similarities
with many other metal (hydr)oxides. By employing quantum molecular dynamics
simulations (metadynamics combined with the Blue Moon ensemble approach), we
unveil the mechanistic pathways and rates of both nonreductive and reductive
dissolution of iron from the (110) and (021) goethite facets in aqueous
solutions at room temperature. Our simulations reveal the interplay between
concerted internal (structural) and external (from solution) protonation as
essential for breaking Fe-O bonds, as well
as for stabilizing intermediate configurations of dissolving Fe. We demonstrate
specifically how Fe(III) reduction to Fe(II) yields higher dissolution rates
than the proton-mediated pathway, while the most rapid dissolution is expected
for these two processes combined, in agreement with experiments.</p>
Iron Dissolution from Goethite (α-FeOOH) Surfaces in Water by Ab Initio Enhanced Free Energy Simulations
