The role of defects and excess surface charges at finite temperature for optimizing oxide photoabsorbers

Abstract

Computational screening of materials for solar to fuel conversion technologies has mostly focused on bulk properties, thus neglecting the structure and chemistry of surfaces and interfaces with water. We report a finite temperature study of WO3, a promising anode for photoelectrochemical cells, carried out using first-principles molecular dynamics simulations coupled with many-body perturbation theory. We identified three major factors determining the chemical reactivity of the material interfaced with water: the presence of surface defects, the dynamics of excess charge at the surface, and finite temperature fluctuations of the surface electronic orbitals. These general descriptors are essential for the understanding and prediction of optimal oxide photoabsorbers for water oxidation.

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Fig. 1: Potential energy of the oxygen-deficient surface of WO3, and charge distribution in singlet and triplet configurations (T = 0).
Fig. 2: Localization of valence band holes and excess electrons at the defective WO3 surface.
Fig. 3: Excess charge distribution and dynamics at the surface at finite T.
Fig. 4: Polarons in bulk WO3 as a function of vacancy concentration.
Fig. 5: Electronic levels at the WO3 oxygen-deficient surface and the aqueous interface.
Fig. 6: Energy levels alignment of the band edges of defective WO3, relative to the redox potential of water in vacuo, at T = 0, and for the solvated surface at finite T.

Data availability

Data related to this publication are organized using the Qresp software and will be available online at http://www.qresp.org/Exploration.html and include a Jupyter notebook used to generate all of the figures reported in the manuscript.

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Acknowledgements

This work was supported by the NSF-CCI grant CHE-1305124, using codes developed within the Midwest Integrated Center for Computational Materials (MICCoM) as part of the Computational Materials Sciences Program funded by the US Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES), Materials Sciences and Engineering Division. We thank Z.-X. Shen, T. Cuk, T. Lian and Y. Ping for numerous discussions.

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Matteo G. and G.G. conceived and designed the calculations. Matteo G. performed the calculations, with numerous discussions with F.G. and Marco G. The manuscript was written primarily by Matteo G. and G.G. All authors discussed the results and commented on the manuscript.

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Correspondence to Giulia Galli.

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Gerosa, M., Gygi, F., Govoni, M. et al. The role of defects and excess surface charges at finite temperature for optimizing oxide photoabsorbers. Nature Mater 17, 1122–1127 (2018). https://doi.org/10.1038/s41563-018-0192-4

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