CO2 Photoreduction on Metal Oxide Surface Is Driven by Transient Capture of Hot Electrons: Ab Initio Quantum Dynamics Simulation

The most critical bottleneck in CO2 photoreduction lies in the activation of CO2 to form an anion radical, CO2•-, or other intermediates by the photoexcited electrons, because CO2 has a high-energy lowest unoccupied molecular orbital (LUMO). Taking rutile TiO2(110) as a prototypical surface, we use time-dependent ab initio nonadiabatic molecular dynamics simulations to reveal that the excitation of bending and antisymmetric stretching vibrations of CO2 can sufficiently stabilize the CO2 LUMO below the conduction band minimum, allowing it to trap photoexcited hot electrons and get reduced. Such vibrational excitations occur by formation of a transient CO2•- adsorbed in an oxygen vacancy. CO2 can trap the hot electrons for nearly 100 fs and dissociate to form CO within 30-40 fs after the trapping. We propose that the activation of the CO2 bending and antisymmetric stretching vibrations driven by hot electrons applies to other CO2 reduction photocatalysts and can be realized by different techniques and material design.