CO2dissociation activated through electron attachment on the reduced rutile TiO2(110)-1×1 surface

Converting CO${}_{2}$ to useful compounds through the solar photocatalytic reduction has been one of the most promising strategies for artificial carbon recycling. The highly relevant photocatalytic substrate for CO${}_{2}$ conversion could be the popular TiO${}_{2}$ surfaces. However, the lack of accurate measurements for the energy level alignment that determines the CO${}_{2}$ reduction on TiO${}_{2}$ has limited our ability to control these complicated photocatalysis processes. We report here a systematic study on the reduction of CO${}_{2}$ at specific sites of the rutile TiO${}_{2}$(110)-$1\ifmmode\times\else\texttimes\fi{}1$ surface using scanning tunneling microscopy at 80 K. The dissociation of CO${}_{2}$ molecules is found to be activated by one electron attachment process with an energy threshold of 1.8 eV above the Fermi level (or 1.4 eV above the TiO${}_{2}$ conduction band onset), while the lowest unoccupied molecular orbital (LUMO) of the adsorbed CO${}_{2}$ is located at 2.3 eV with respect to the Fermi level. The observed dependence of the dissociation rate on the tunneling current suggests that the reduction of CO${}_{2}$ induced by the electron attachment is a single electron process. These practical information can be used to guide the design of effective catalysts for CO${}_{2}$ photoreduction.