Abstract
The band edge positions of semiconductors determine functionality in solar water splitting. While ligand exchange is known to enable modification of the band structure, its crucial role in water splitting efficiency is not yet fully understood. Here, ligand‐engineered manganese oxide cocatalyst nanoparticles (MnO NPs) on bismuth vanadate (BiVO4) anodes are first demonstrated, and a remarkably enhanced photocurrent density of 6.25 mA cm−2 is achieved. It is close to 85% of the theoretical photocurrent density (≈7.5 mA cm−2) of BiVO4. Improved photoactivity is closely related to the substantial shifts in band edge energies that originate from both the induced dipole at the ligand/MnO interface and the intrinsic dipole of the ligand. Combined spectroscopic analysis and electrochemical study reveal the clear relationship between the surface modification and the band edge positions for water oxidation. The proposed concept has considerable potential to explore new, efficient solar water splitting systems.
Highlights
We studied the ligand engineering of manganese oxide nanoparticles (MnO NPs) to enhance the photoactivity of BiVO4-based anodes, and found that BF4-treated MnO/BiVO4/WO3 showed superior PEC properties to the Ca–ethylenediaminetetraacetic acid (EDTA)-treated MnO/BiVO4/WO3, due to the wellaligned band edge position of the BF4-treated MnO/BiVO4/WO3 photoelectrode
The improved PEC performance of these photoelectrodes is due to their higher charge generation and separation rate through the modification of the band structure, which enables forceful water oxidation
The trends in the energy level position between the different ligands are confirmed by ultraviolet photoelectron spectroscopy (UPS) measurement, showing the observed result from contributions from the both the MnO–ligand interface dipole and the intrinsic dipole moment of the ligand molecule itself
Summary
Sub-10 nm sized MnO NPs were prepared by previously reported hot-injection methods.[32,33,35] During the synthesis procedure, MnO NPs are covered with fatty acid surfactants, myristic acids, which are used to maintain uniform sized particles. This reveals that reducing the the bonding. BF4-treated MnO NPs act as an efficient charge transfer mediator for PEC water splitting
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