Mechanistic Understanding on the Role of Cu Species over the CuO(x)/TiO(2) Catalyst for CO(2) Photoreduction

[Image: see text] Incorporation of earth-abundant Cu is one of the most important approaches to improve the practicability of TiO(2) for photoreduction of CO(2) into value-added solar fuels. However, the molecular insight on the role of Cu is complicated and far from understood. We performed a first principle calculation on the anatase (101) surface modified by a single Cu atom deposited on the surface (Cu(S)) or doped in the lattice (Cu(L)). It is demonstrated the Cu(L) is clearly more stable than the Cu(S) and could promote the formation of oxygen vacancy (Vo) greatly. The Cu(S) plays a role of donor, while the Cu(L) is electronically deficient and becomes a global electron trapper. If a Vo is introduced, the excess electrons would immigrate to the empty gap state of the Cu(L) and make it half-filled in some case, which implies its metallic characters and improved conductivity; meanwhile, the formation of Ti(3+) is suppressed. Judging from the adsorption energies, it is the Vo that primarily improves the adsorption of CO(2) in both linear and bent states, and the Cu(S) could hardly stabilize CO(2) more, while the promotion effect of Vo could even be counteracted by the Cu(L) due to its electronic deficiency. The reduction pathways (CO(2)* → CO* + O*) show that, with the assistance of the Cu(S), linear CO(2) could directly transform into the carbonate-like geometry vertically binding to the surface, and the intermediate configuration of the bent CO(2) horizontally bridging the Vo could be successfully skipped. Therefore, the barrier of the rate-determining transformation could be lowered from 0.75 to 0.39 eV. Furthermore, it is found the strong adsorption of the produced CO by the Cu(S) might retard the smooth going of the catalytic process.