Crystallographic Control of the Initial Electrochemical Reduction of Hematite

Abstract Electrochemical reduction of iron oxides enables low-temperature, sustainable iron production, yet how crystallographic orientation affects the initial reduction of hematite remains unclear. Here, we combine density functional theory + U calculations and ab initio molecular dynamics to study the initial electrochemical reduction of the \(\:\left(0001\right),\left(10\stackrel{-}{1}0\right)\), and (\(\:1\stackrel{-}{2}10)\) facets of α-Fe 2 O 3 at different hydrogen coverages. The potential-dependent descriptor G max ( U ) reveals a pronounced crystallographic dependence: the \(\:\left(0001\right)\) facet consistently exhibits the lowest limiting free-energy span and thus the highest thermodynamic reduction propensity. High hydrogen coverage, the thermodynamically preferred surface state under cathodic conditions, leaves \(\:\left(0001\right)\) and \(\:\left(10\stackrel{-}{1}0\right)\) essentially unaffected but strongly suppresses the reduction of (\(\:1\stackrel{-}{2}10)\), revealing facet-dependent surface passivation. Upon reduction, a more metallic, Fe-rich surface forms, and the O p-band center shifts most strongly on \(\:\left(0001\right)\). The predicted preference for \(\:\left(0001\right)\) agrees with experiments on the hydrogen reduction of hematite single crystals, pointing to an intrinsic facet dependence of reducibility. Our results identify crystallographic orientation and interfacial hydrogenation as key factors in the initial electrochemical reduction of hematite and provide atomistic guidelines for controlling electrochemical iron extraction.