Abstract
Ascertaining the role of in-plane intrinsic defects and edge atoms of 2D transition metal dichalcogenides is necessary for developing efficient artificial leaves. This talk presents the photocatalytic CO2 reduction to CH4 over reconstructed edge atoms of 2H-WSe2 monolayers grown by low-pressure vapor deposition. The atomic configurations of the in-plane defects and imperfect edges are investigated by density functional theory calculations and scanning transmission electron microscopy, respectively. Low-temperature and time-resolved photoluminescence spectroscopies illustrate the existence of defect-related excitons and prolonged exciton lifetime for the smaller flakes. Photocatalytic results show that the solar-to-CH4 internal quantum efficiency is the reciprocal function of the flake size, reaching a maximum value of 0.2%. It also indicates that the consumed electron rate is about 3.8 electrons per second per edge atom, which is two orders of magnitude larger than the in-plane intrinsic defects. Theoretical calculations affirm the presence of linear and bent adsorbed CO2 molecules with edge atoms. Moreover, atomic force microscopy-based scanning electrochemical microscopy with nanoscale resolution at the monolayer WSe2–liquid interface confirms that the edge is the most preferred region for charge transfer and transport. These results pave the way for designing a new class of 2D materials with reconstructed edges as a non-precious catalyst for hydrogen evolution or CO2 reduction reactions.