• Sun, Xin
• Tiwari, Devendra
• Fermín, David J.

Abstract

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 the Pc21n space group, as confirmed by XRD 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 Fe3+ sites. DFT-HSE06 electronic structure calculations show GFO is highly ionic with very low dispersion in the valence band maximum (VBM) and conduction band minima (CBM). Electrochemical impedance spectroscopy reveals n-type conductivity with a flat band potential (Ufb) of 0.52 V vs RHE, indicating that GFO has the most positive CBM reported of any ferrite. The photoelectrochemical oxidation of SO32- shows an ideal semiconductor-electrolyte interfacial behavior with no evidence of surface recombination down to the Ufb. Surprisingly, the onset potential for the oxygen evolution reaction also coincides with the Ufb, 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.

Topics

• impedance spectroscopy
• dispersion
• surface
• phase
• x-ray diffraction
• thin film
• Oxygen
• semiconductor
• Hydrogen
• density functional theory
• Raman spectroscopy
• space group