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Surface Fe vacancy defects on haematite and their role in the light-induced water splitting in artificial photosynthesis

Abstract

Haematite (α-Fe2O3) is a potential candidate for photo-electrochemical water splitting. It is abundant and its electronic properties fit those needed for this kind of device. However, very little is known about the intermediate steps of this photon-induced water splitting process. We here propose that surface iron vacancies can be the main defects responsible for the activity of haematite in the photoelectrochemical reaction. We perform DFT+U calculations and explicitly add holes to show that these defects are common in iron-terminated (0001) surfaces. As holes tend to be localized at these centers, they should be available for the water dissociation under sunlight. Our calculations also reveal that the water adsorption energy close to the vacancy is 1eV stronger than far from it, and when the formation of multi-holes are considered, a thermodynamically stable water dissociation mechanism can be constructed. We determined that both Fe=O and Fe-OOH intermediate steps are stable, although Fe-OOH quickly leads to the formation of O2, having therefore a very short lifetime. Phonon calculations on these structures reveal the appearance of peaks in the 800-900cm-1 frequency range only for the intermediate steps, connected to Fe=O vibrations, in agreement with recent measurements.

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Publication details

The article was received on 25 Sep 2017, accepted on 06 Nov 2017 and first published on 06 Nov 2017


Article type: Paper
DOI: 10.1039/C7CP06558B
Citation: Phys. Chem. Chem. Phys., 2017, Accepted Manuscript
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    Surface Fe vacancy defects on haematite and their role in the light-induced water splitting in artificial photosynthesis

    F. R. Negreiros, L. Pedroza, F. L. Souza and G. Dalpian, Phys. Chem. Chem. Phys., 2017, Accepted Manuscript , DOI: 10.1039/C7CP06558B

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