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

Abstract

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, ...