We performed systematic study on electronic structures and photoelectrochemical (PEC)
properties of ilmenite-type MTiO3 (M = Mn, Fe, Co, and Ni) thin-film photoanodes for water
oxidation reactions. Single-phase MTiO3 films were grown on α-Al2O3 substrates by using
pulsed-laser deposition. Formation of the ilmenite-type structures and oxidation states of
M2+Ti4+O3 were revealed by X-ray diffraction and X-ray absorption spectroscopy, respectively.
The PEC performance in water was investigated by linear sweep voltammetry under Xe-lamp
illumination and incident photon to conversion efficiency measurements under monochromatic
illumination. We found that NiTiO3 acted as the most effective photoanode among MTiO3. The
mechanism of the different PEC performance was discussed from the viewpoint of the electronic
structures investigated by photoemission spectroscopy and band calculation based on density
functional theory. We revealed that the stronger hybridization between O 2p and M 3d states was
responsible for the more efficient photoanodic activity among ilmenite-type MTiO3.
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