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

Abstract

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 <i>ab initio</i> 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.