CO2 dissociation activated through electron attachment on the reduced rutile TiO2(110)-1x1 surface

Converting CO2 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 CO2 conversion could be the popular TiO2 surfaces. However, the lack of accurate measurements for the energy level alignment that determines the CO2 reduction on TiO2 has limited our ability to control these complicated photocatalysis processes. We report here a systematic study on the reduction of CO2 at specific sites of the rutile TiO2(110)-1 x 1 surface using scanning tunneling microscopy at 80 K. The dissociation of CO2 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 TiO2 conduction band onset), while the lowest unoccupied molecular orbital (LUMO) of the adsorbed CO2 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 CO2 induced by the electron attachment is a single electron process. These practical information can be used to guide the design of effective catalysts for CO2 photoreduction.