Journal
ACS CATALYSIS
Volume 6, Issue 7, Pages 4769-4774Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acscatal.6b01138
Keywords
water oxidation; photocatalysis; titanium dioxide; density functional theory; activation energy; oxygen exchange
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Funding
- DoE-BES, Division of Chemical Sciences, Geosciences, and Biosciences [DE-FG02-12ER16286]
- DoE [DE-AC02-05CH11231]
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The photocatalytic oxidation of water to molecular oxygen is a key step toward the conversion of solar energy to fuels. Understanding the detailed mechanism and kinetics of this reaction is important for the development of robust catalysts with improved efficiency. TiO2 is one of the best-known photocatalysts as well as a model system for the study of the oxygen evolution reaction (OER). Here we use hybrid density functional based energetic calculations and first-principles molecular dynamics simulations to investigate the pathway and kinetics of the OER on the majority (101) surface of anatase TiO2 in a water environment. Our results show that terminal Ti-OH groups are stable intermediates at the aqueous (101) interface, in accord with the experimental observation that OH radicals are efficiently produced on anatase. Oxidation of Ti-OH gives rise to a second stable intermediate, a surface-bridging peroxo dimer ((O-2(2-))(br)) composed of one water and one surface lattice oxygen atom, consistent with the surface peroxo intermediates revealed by in situ measurements on rutile. Our calculations further predict that molecular oxygen evolves directly from (O-2(2-))(br) through a concerted two-electron transfer, thus leading to oxygen exchange between TiO2 and the adsorbed species. Oxygen exchange is found to be negligible on rutile, so that different OER pathways are likely to be operative on the two main TiO2 polymorphs. This difference could explain the observed lower OER activity of anatase relative to rutile.
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