Abstract
Elucidating the structure of the interface between natural (reduced) anatase TiO2 (101) and water is an essential step toward understanding the associated photoassisted water splitting mechanism. Here we present surface X-ray diffraction results for the room temperature interface with ultrathin and bulk water, which we explain by reference to density functional theory calculations. We find that both interfaces contain a 25:75 mixture of molecular H2O and terminal OH bound to titanium atoms along with bridging OH species in the contact layer. This is in complete contrast to the inert character of room temperature anatase TiO2 (101) in ultrahigh vacuum. A key difference between the ultrathin and bulk water interfaces is that in the latter water in the second layer is also ordered. These molecules are hydrogen bonded to the contact layer, modifying the bond angles.
Highlights
E ver since Honda and Fujishima[1] demonstrated photoassisted water splitting on titanium dioxide (TiO2), it has been widely investigated for hydrogen fuel production.[2]
We find that a mixture of molecular and dissociated water is present in the contact layer, pointing to a significantly enhanced reactivity of the substrate compared with that observed in UHV
Previous calculations of the A101/water interface predict that the formation of OHt species from water dissociation is coupled with the formation of OHbr species that trap excess electrons from the selvedge.[10]
Summary
Previous calculations of the A101/water interface predict that the formation of OHt species from water dissociation is coupled with the formation of OHbr species that trap excess electrons from the selvedge.[10] In principle, this can be probed experimentally by the position of the O2c to which a H atom is bound to form OHbr.[27] Our SXRD results indicate that, after H2O exposure, the Ti5c−O2c bond length increases from 1.90 ± 0.02 Å to 1.95 ± 0.01 Å and 1.88 ± 0.01 Å to 1.95 ± 0.01 Å, respectively for the ultrathin water film and bulk water interfaces. Experimental and computational methods, CTRs with the best fit for the A101 interface with an ultrathin water film and the A101 interface with bulk water, and a χ2n graph highlighting the change in χ2n against a change in surface adsorbate coverage (PDF)
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