High Interfacial Hole-Transfer Efficiency at GaFeO_3 Thin Film Photoanodes

摘要

The photoelectrochemical properties of polycrystalline GaFeO3(GFO) thin films are investigated for the first time. Thin films prepared by sol-gel methods exhibit phase-pure orthorhombic GFO with thePc21nspace group, as confirmed by X-ray diffraction and Raman spectroscopy. Optical responses are characterized by a 2.72 eV interband transition and sub-bandgap d-d transitions associated with octahedral and tetrahedral coordination of Fe(3+)sites. DFT-HSE06 electronic structure calculations show GFO is highly ionic with very low dispersion in the valence band maximum (VBM) and conduction band minimum (CBM). Electrochemical impedance spectroscopy reveals n-type conductivity with a flat band potential (U-fb) of 0.52 V versus reversible hydrogen electrode, indicating that GFO has the most positive CBM reported of any ferrite. The photoelectrochemical oxidation of SO(3)(2-)shows an ideal semiconductor-electrolyte interfacial behavior with no evidence of surface recombination down to theU(fb). Surprisingly, the onset potential for the oxygen evolution reaction also coincides with theU(fb), showing interfacial hole-transfer efficiency above 50%. The photoelectrochemical properties are limited by bulk recombination due to the short-diffusion length of minority carriers as well as slow transport of majority carriers. Strategies towards developing high-efficiency GFO photoanodes are briefly discussed.