RESUMO
Incorporation of earth-abundant Cu is one of the most important approaches to improve the practicability of TiO2 for photoreduction of CO2 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 (CuS) or doped in the lattice (CuL). It is demonstrated the CuL is clearly more stable than the CuS and could promote the formation of oxygen vacancy (Vo) greatly. The CuS plays a role of donor, while the CuL 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 CuL and make it half-filled in some case, which implies its metallic characters and improved conductivity; meanwhile, the formation of Ti3+ is suppressed. Judging from the adsorption energies, it is the Vo that primarily improves the adsorption of CO2 in both linear and bent states, and the CuS could hardly stabilize CO2 more, while the promotion effect of Vo could even be counteracted by the CuL due to its electronic deficiency. The reduction pathways (CO2* â CO* + O*) show that, with the assistance of the CuS, linear CO2 could directly transform into the carbonate-like geometry vertically binding to the surface, and the intermediate configuration of the bent CO2 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 CuS might retard the smooth going of the catalytic process.