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Electrochemical oxidation of hematite ({\alpha}-Fe2O3) nano-particulate filmsat 600 mV vs. Ag+/AgCl reference in KOH electrolyte forms a species at thehematite surface which causes a new transition in the upper Hubbard bandbetween the Fe(3d)-O(2p) state region and the Fe(4sp)-O(2p) region, asevidenced by oxygen near edge x-ray absorption fine structure (NEXAFS) spectra.The electrochemical origin of this transition suggests that it is related witha surface state. This transition, not known for pristine {\alpha}-Fe2O3 is atabout the same x-ray energy, where pristine 1% Si doped Si:Fe2O3 has suchtransition. Occurrence of this state coincides with the onset of an oxidativedark current wave at around 535 mV - a potential range, where the tunnelingexchange current has been previously reported to increase by three orders ofmagnitude with the valence band and the transfer coefficient by a factor of 10.Oxidation to only 200 mV does not form such extra NEXAFS feature, supportingthat a critical electrochemical potential between 200 and 600 mV is necessaryto change the electronic structure of the iron oxide at the surface. Decreaseof the surface roughness, as suggested by visual inspection, profilometry andx-ray reflectivity, points to faceting as potential structural origin of thesurface state.

Evolution of an oxygen NEXAFS transition in the upper Hubbard band in {\alpha}-Fe2O3 upon electrochemical oxidation