Thermally Oxidized Iron Electrodes for Photoelectrochemical Application

Air‐oxidized and CO2‐treated laminar iron electrodes have been characterized structurally (X‐ray diffraction) and photoelectrochemically (photocurrent, polarization, cyclic voltammetry, flat‐band and static potential, band‐gap and cell characteristics) in order to elucidate the role of Fe2+ and Fe3+ at the semiconductor‐electrolyte interface in the photooxidation of H2O. Surface Fe2+ increases the band‐gap and the electron‐hole recombination rate; Fe3+ causes electroreduction of O2, which is followed by oxidation of Fe2+ (Fe3O4 → Fe2O3). This affects the catalytic activity for dissociative water adsorption as Fe2+ on non‐stoichiometric α‐Fe2O3 acts as the active site.