Electronic structure and interface energetics of CuBi2O4 photoelectrodes - data

In this study, the electronic structure of CuBi₂O₄ has been studied by a combination of hard X-ray photoemission, resonant photoemission and X-ray absorption spectroscopies, and compared with density functional theory (DFT) calculations. The photoemission study indicates that there is a strong Bi 6s-O 2p hybrid electronic state at 2.3 eV below the Fermi level, whereas the valence band maximum (VBM) has a predominant Cu 3d – O 2p hybrid character. XAS at the O K-edge supported by DFT calculations provides a good description of the conduction band, indicating that the conduction band minimum (CBM) is composed of unoccupied Cu 3d-O 2p states. The combined experimental and theoretical results suggest that the low charge carrier mobility for CuBi₂O₄ derives from an intrinsic charge localization at the VBM. Also, the low-energy visible light absorption in CuBi₂O₄ may result from a direct but forbidden Cu d–d electronic transition, leading to a low absorption coefficient. Additionally, the ionization potential (IP) of CuBi₂O₄ is higher than that of the related binary oxide CuO or that of NiO, which is commonly used as hole transport/extraction layer in photoelectrodes. This work provides solid electronic basis for topical materials science approaches to increase the charge transport and improve the photoelectrochemical properties of CuBi₂O₄-based photoelectrodes.

Data comprise:

Valence band photoemission spectra of CuBi2O4 taken using photon energies near the Cu L3.
Cu L3 X-ray absorption spectrum of CuBi2O4 indicating the selected photon energies for the resonant photoemission experiment.
Valence band photoemission of CuBi2O4 near the Fermi level showing the spectral intensity difference between on-resonance (at hν = 933.1 eV) and off-resonance (at hν = 929.8 eV) spectra.
Experimental VB photoemission spectra of CuBi2O4 measured with 1486 eV (Al Kα1), 4068 eV, and 8133 eV ionizing photon energy.
Photoionization cross section dependence on the ionizing photon energy for valence orbitals in CuBi2O4.
Calculated VB photoemission spectra of CuBi2O4 at 8133 eV ionizing photon energy.
O K-edge XAS of CuBi2O4 along with that of CuO for comparison.
Empty PDOS from DFT calculations for CuBi2O4; the O K-edge
XAS is included in the same scale for comparison. (C) UV−vis absorption spectrum of CuBi2O4.
Measured and calculated electron affinity (CBM) and ionization potential (VBM) of CuBi2O4, CuO, and NiO with respect to the vacuum level.
Chopped-light linear sweep voltammetry scans for CuBi2O4 (black) and NiO/CuBi2O4 (red) photoelectrodes.
Chopped-light linear sweep voltammetry scans for CuO (black) and NiO/CuO (red) photoelectrodes.
PEC measurements were done in 0.2 M K2SO4 + 0.1M phosphate buffer solution (pH 6.8) with 0.3% w/w H2O2.

Research results based upon these data are published at https://doi.org/10.1021/acs.jpcc.0c08455