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Pinning of the Fermi Level in CuFeO 2 by Polaron Formation Limiting the Photovoltage for Photochemical Water Splitting
Author(s) -
Hermans Yannick,
Klein Andreas,
Sarker Hori Pada,
Huda Mohammad N.,
Junge Henrik,
Toupance Thierry,
Jaegermann Wolfram
Publication year - 2020
Publication title -
advanced functional materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 6.069
H-Index - 322
eISSN - 1616-3028
pISSN - 1616-301X
DOI - 10.1002/adfm.201910432
Subject(s) - materials science , fermi level , photocathode , polaron , water splitting , x ray photoelectron spectroscopy , heterojunction , condensed matter physics , electron , photocatalysis , optoelectronics , chemistry , nuclear magnetic resonance , physics , biochemistry , quantum mechanics , catalysis
CuFeO 2 is recognized as a potential photocathode for photo(electro)chemical water splitting. However, photocurrents with CuFeO 2 ‐based systems are rather low so far. In order to optimize charge carrier separation and water reduction kinetics, defined CuFeO 2 /Pt, CuFeO 2 /Ag, and CuFeO 2 /NiO x (OH) y heterostructures are made in this work through a photodeposition procedure based on a 2H CuFeO 2 hexagonal nanoplatelet shaped powder. However, water splitting performance tests in a closed batch photoreactor show that these heterostructured powders exhibit limited water reduction efficiencies. To test whether Fermi level pinning intrinsically limits the water reduction capacity of CuFeO 2 , the Fermi level tunability in CuFeO 2 is evaluated by creating CuFeO 2 /ITO and CuFeO 2 /H 2 O interfaces and analyzing the electronic and chemical properties of the interfaces through photoelectron spectroscopy. The results indicate that Fermi level pinning at the Fe 3+ /Fe 2+ electron polaron formation level may intrinsically prohibit CuFeO 2 from acquiring enough photovoltage to reach the water reduction potential. This result is complemented with density functional theory calculations as well.