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High Interfacial Hole‐Transfer Efficiency at GaFeO 3 Thin Film Photoanodes
Author(s) -
Sun Xin,
Tiwari Devendra,
Fermin David J.
Publication year - 2020
Publication title -
advanced energy materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 10.08
H-Index - 220
eISSN - 1614-6840
pISSN - 1614-6832
DOI - 10.1002/aenm.202002784
Subject(s) - materials science , raman spectroscopy , dielectric spectroscopy , orthorhombic crystal system , thin film , band gap , semiconductor , electrochemistry , chemical physics , electrode , optoelectronics , nanotechnology , crystallography , chemistry , crystal structure , optics , physics
Abstract The photoelectrochemical properties of polycrystalline GaFeO 3 (GFO) thin films are investigated for the first time. Thin films prepared by sol–gel methods exhibit phase‐pure orthorhombic GFO with the Pc 21 n space 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 the U fb . Surprisingly, the onset potential for the oxygen evolution reaction also coincides with the U 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.