Synergy between Defects, Photoexcited Electrons, and Supported Single Atom Catalysts for CO2 Reduction

Dispersed atomic catalysts can achieve high catalytic efficiency and have the potential to enable chemical transformation of inert molecules like CO 2 . The effect of surface defects on photocatalytic reduction of CO 2 using supported single atom catalysts however requires clarification. Using density functional theory and experimental techniques, we have investigated the role of surface oxygen vacancies (O v ) and photoexcited electrons on supported single atom Cu catalysts and CO 2 reduction. Adsorption of Cu was strong to the TiO 2 surface, and charges of the Cu atoms were highly dependent on whether surface defects were present. Cu atoms with O v aided in the adsorption of activated bent CO 2, which is key to CO 2 reduction. Our results also show that CO 2 dissociation (CO 2 * → CO* + O*), which is a proposed initial step of CO 2 reduction to hydrocarbon products, occurs very readily for a single Cu atom in an O v, with barriers of ∼0.19 eV. Such low barriers do not occur with Cu over a stoichiometric surface. Furthermore, the presence of a photoexcited electron leads to a substantial increase in reaction rate for Cu over a stoichiometric surface; the Cu/TiO 2 surface is largely inert in the absence of photoexcited electrons. Experimental results corroborate these theoretical calculations and show that activation of CO 2 occurs most readily for TiO 2 catalysts with dispersed Cu and O v . CO 2 photoreduction also occurs most readily for TiO 2 catalysts with dispersed Cu and O v, compared to TiO 2 or Cu over stoichiometric TiO 2 catalysts. We also modeled atomic Pt to understand how metals besides Cu may behave. We found that Pt over TiO 2 also activates CO 2 but that dissociation of CO 2 over Pt with O v does not occur as readily as for Cu with O v . Our results show that tailoring TiO 2 surfaces with defects in conjunction with specific atomic catalysts like Cu may lead to fast desirable photoreduction of CO 2 .