Recently, the team of professor Zhao Jin of the School of Physics, University of Science and Technology of China and the International Research Center for Quantum Design of Functional Materials (ICQD) of the National Research Center for Microscale Material Science in Hefei made new progress in the study of the mechanism of CO2 photoreduction on oxide surfaces. The first-principles development of the excited state dynamics program reveals that CO2 molecules on the surface of oxides can excite the bending and asymmetric stretching vibration modes of CO2 molecules by briefly capturing electrons, reducing the energy of CO2 LUMO orbits, making CO2 molecules Capable of capturing photoelectrons and reducing reactions. The result of this study was published in "Journal of the American Chemical Society" as the title of CO2 Photoreduction on Metal Oxide Surface is Driven by Transient Capture of Hot Electrons: Ab initio Quantum Dynamics Simulation [J. Am. Chem. Soc. 142, 6, 3214 ( 2020)]. The first author Chu Weibin obtained a Ph.D. from the Hefei National Research Center for Microscale Physical Sciences, and Zhao Jin is the corresponding author.
CO2 photoreduction on solid surfaces has always been a challenging scientific problem. The main bottleneck lies in the high LUMO orbital energy of CO2 molecules, which makes it difficult to capture photo-excited thermal electrons to produce reduction reactions. The team of Zhao Jin used the self-developed first-principles excited state kinetics software Hefei-NAMD to study the CO2 photoreduction mechanism on the surface of TiO2. The study found that because the CO2 molecule's LUMO energy is higher than the TiO2's conduction band bottom energy, it is difficult for the CO2 molecule to capture electrons stably. Within a certain lifetime, the electrons on the CO2 will decay back to the TiO2 conduction band. However, if CO2 is adsorbed on the oxygen defect site of TiO2, and the lifetime of its electron trapping can exceed 12 femtoseconds, forming a short-lived CO2.-, then the two vibration modes of bending and asymmetric stretching of the CO2 molecule will be effective Excitation can reduce the LUMO orbital energy of CO2 below the conduction band of TiO2 and keep it for about 150 fs. At this time, CO2 can effectively capture the electrons in the conduction band within 80 fs, and after 30- 40 fs dissociates to form CO molecules. This work reveals the key role of CO2 vibration mode excitation in the photoreduction process, and gives a clear description of the excited state kinetics of photoreduction of CO2 molecules on the surface of TiO2 from the perspective of first-principles calculations.
This work is another important application of Hefei-NAMD software. Since 2016, nearly 30 academic papers have been published using this software.
This work is supported by the Fund Committee, the Ministry of Science and Technology, Anhui Province, etc.
Photo caption: CO2 photodissociation process on TiO2 surface. (1) Light excitation generates transient CO2.-; (2) When CO2.- life is greater than 12fs, bending vibration mode and asymmetric tensile vibration mode are excited, and CO2 LUMO is reduced to within 10 fs Below the conduction band; (3) CO2 captures hot electrons within 80 fs and reforms into stable CO2.-; (4) CO2.- dissociates after 30-40 fs.
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