Understanding the Effect of *CO Coverage on C-C Coupling toward CO 2 Electroreduction.

Cu-based tandem nanocrystals have been widely applied to produce multicarbon (C 2+ ) products via enhancing CO intermediate (*CO) coverage toward CO 2 electroreduction. Nevertheless, it remains ambiguous to understand the intrinsic correlation between *CO coverage and C-C coupling. Herein, we constructed a tandem catalyst via coupling CoPc with the gas diffusion electrode of Cu (GDE of Cu-CoPc). A faradaic efficiency for C 2+ products of 82% was achieved over a GDE of Cu-CoPc at an applied current density of 480 mA cm -2 toward CO 2 electroreduction, which was 1.8 times as high as that over the GDE of Cu. Based on in situ experiments and density functional theory calculations, we revealed that the high *CO coverage induced by CO-generating CoPc promoted the local enrichment of *CO with the top adsorption mode, thus reducing the energy barrier for the formation of OCCO intermediate. This work provides an in-depth understanding of the surface coverage-dependent mode-specific C-C coupling mechanism toward CO 2 electroreduction.