Nanoscale Solvation Leads to Spontaneous Formation of a Bicarbonate Monolayer on Rutile (110) under Ambient Conditions: Implications for CO2 Photoreduction

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• 作者：Anqi Song ; Erik S. Skibinski ; William J. I. DeBenedetti ; Amnon G. Ortoll-Bloch ; Melissa A. Hines
• 刊名：Journal of Physical Chemistry C
• 出版年：2016
• 出版时间：May 5, 2016
• 年：2016
• 卷：120
• 期：17
• 页码：9326-9333
• 全文大小：532K
• 年卷期：0
• ISSN：1932-7455

文摘

The chemical state of a catalyst in operando is particularly important for catalysts that target minority species, such as atmospheric CO₂ which has a concentration of only 400 ppm. A reaction can be promoted by the selective binding of reactants or hindered by molecules that block active sites. We show that adsorbed CO₂, a very weakly bonded species on TiO₂, is unlikely to play the key role in CO₂ photoreduction under ambient conditions, at least on rutile (110), as the vast majority of unsaturated Ti sites are terminated by a different, much more strongly bound carbonaceous species: adsorbed bicarbonate (HCO₃). Using a combination of scanning tunneling microscopy (STM) and surface spectroscopies, we show that atmospheric CO₂ readily and stably displaces adsorbed H₂O on rutile (110), creating a self-assembled monolayer of HCO₃ and H that is stable at room temperature even in vacuum. This reaction occurs on near-ideal, stoichiometric rutile (110) and does not require surface defects, such as O vacancies, Ti interstitials, or steps. This reaction is promoted both by the strong bidentate bonding of HCO₃ as well as the nanoscale H₂O film that spontaneously forms on TiO₂ under ambient conditions. Density functional theory calculations show that the nanoscale water layer adsorbed to rutile (110) solvates the products and changes the reaction energetics significantly. The chemical state of the catalyst in operando will also be affected by the half-monolayer of adsorbed H produced by the reactive dissociation of H₂O.