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

Cu-based tandem nanocrystals have been widely applied to produce multicarbon (C) products via enhancing CO intermediate (*CO) coverage toward CO 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 products of 82% was achieved over a GDE of Cu-CoPc at an applied current density of 480 mA cm toward CO electroreduction, which was 1.8 times as high as that over the GDE of Cu. Based on 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 electroreduction.