Dynamic intragap Ce 4f states in CeTi₂O₆ photoanodes revealed by Dip&Pull RPES
Abstract
Photoelectrochemical (PEC) water splitting, a promising route for solar fuel production, typically relies on oxidatively-stable metal oxide photoanodes, that can involve multiple metal cations. However, the solar conversion efficiency of these materials is often severely limited by intragap states acting as recombination centers. Unfortunately, the origin, chemical nature and evolution of these defect-related states are difficult to track under operating conditions. Here, we aim to bridge this knowledge gap by combining resonant photoelectron spectroscopy (RPES), near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS), and “Dip&Pull” NAP-XPS. We demonstrate this approach on CeTi2O6 (CTO), a candidate ternary oxide photoanode, and characterize the solid–electrolyte interface under PEC operating conditions. Our findings reveal that Ce 4f states (∼1.6 eV) dominate the intragap electronic structure, with no contribution from Ti 3d states, establishing Ce as the primary defect center, even after severe reduction. Exposure to water vapor induces an upward band bending (∼0.6 eV) and surface reduction, thereby enhancing intragap Ce 4f content. Under electrochemical operation, Ce3+ species are dominant over a wide anodic potential window (0.0 to 1.5 V vs. RHE), indicating the formation of limiting Ce 4f recombination centers under practical conditions. Most strikingly, in situ RPES uncovers a previously unobserved Ce 4f-related feature at ∼2.8 eV, only visible under electrochemical conditions, highlighting the strong coupling between Ce 4f states and interfacial water. These results not only advance fundamental understanding of Ce-based photoelectrodes but also provide a methodological framework for in situ electronic structure analysis of complex oxides at solid–electrolyte interfaces. They further underscore the need for Ce3+ passivation strategies to mitigate recombination losses in Ce-containing photoabsorbers.
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BibTeX
@article{hachemi2026dynamic,
title = {{Dynamic intragap Ce 4f states in CeTi₂O₆ photoanodes revealed by Dip&Pull RPES}},
author = {C. Hachemi and M. Debbichi and M. Rivera-Salazar and C. Spadetto and J. Gallet and F. Bournel and A. Yaroslavtsev and R. Temperton and A. Shavorskiy and C. Geantet and M. Badawi and M. Prevot and L. Cardenas},
journal = {Journal of Materials Chemistry A},
year = {2026},
month = oct,
doi = {10.1039/d6ta05469b},
url = {https://hal.science/hal-05838784v1},
note = {CC BY-NC 4.0},
}
RIS
TY - JOUR
TI - Dynamic intragap Ce 4f states in CeTi₂O₆ photoanodes revealed by Dip&Pull RPES
AU - C. Hachemi
AU - M. Debbichi
AU - M. Rivera-Salazar
AU - C. Spadetto
AU - J. Gallet
AU - F. Bournel
AU - A. Yaroslavtsev
AU - R. Temperton
AU - A. Shavorskiy
AU - C. Geantet
AU - M. Badawi
AU - M. Prevot
AU - L. Cardenas
PY - 2026
DA - 2026/10/09
JO - Journal of Materials Chemistry A
DO - 10.1039/d6ta05469b
UR - https://hal.science/hal-05838784v1
AB - Photoelectrochemical (PEC) water splitting, a promising route for solar fuel production, typically relies on oxidatively-stable metal oxide photoanodes, that can involve multiple metal cations. However, the solar conversion efficiency of these materials is often severely limited by intragap states acting as recombination centers. Unfortunately, the origin, chemical nature and evolution of these defect-related states are difficult to track under operating conditions. Here, we aim to bridge this knowledge gap by combining resonant photoelectron spectroscopy (RPES), near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS), and “Dip&Pull” NAP-XPS. We demonstrate this approach on CeTi2O6 (CTO), a candidate ternary oxide photoanode, and characterize the solid–electrolyte interface under PEC operating conditions. Our findings reveal that Ce 4f states (∼1.6 eV) dominate the intragap electronic structure, with no contribution from Ti 3d states, establishing Ce as the primary defect center, even after severe reduction. Exposure to water vapor induces an upward band bending (∼0.6 eV) and surface reduction, thereby enhancing intragap Ce 4f content. Under electrochemical operation, Ce3+ species are dominant over a wide anodic potential window (0.0 to 1.5 V vs. RHE), indicating the formation of limiting Ce 4f recombination centers under practical conditions. Most strikingly, in situ RPES uncovers a previously unobserved Ce 4f-related feature at ∼2.8 eV, only visible under electrochemical conditions, highlighting the strong coupling between Ce 4f states and interfacial water. These results not only advance fundamental understanding of Ce-based photoelectrodes but also provide a methodological framework for in situ electronic structure analysis of complex oxides at solid–electrolyte interfaces. They further underscore the need for Ce3+ passivation strategies to mitigate recombination losses in Ce-containing photoabsorbers.
SN - 2050-7488
SN - 2050-7496
ER -