Enhanced Carbon‐Carbon Coupling at Interfaces with Abrupt Coordination Number Changes

Cu‐catalyzed electrochemical CO2 reduction reaction (CO2RR) produces multi‐carbon (C2+) chemicals with considerable selectivities and activities, yet required high overpotentials impede its practical application. Here, we design interfaces with abrupt coordination number (CN) changes that greatly reduce the applied potential for achieving high C2+ Faradaic efficiency (FE). Encouraged by the mechanistic finding that the coupling between *CO and *CO(H) is the most probable C‐C bond formation path, we use Cu2O‐ and Cu‐phthalocyanine‐derived Cu (OD‐Cu and PD‐Cu) to build the interface. Using operando X‐ray absorption spectroscopy (XAS), we find that the Cu CN of OD‐Cu is ~11, favoring CO* adsorption, while the PD‐Cu has a COH*‐favorable CN of ~4. Operando Raman spectroscopy revealed that the interfaces with abrupt CN changes promote *OCCOH formation. As a result, the designed catalyst achieves a C2+ FE of 85±2% at 220 mA cm‐2 in a zero‐gap CO2 electrolyzer. An improvement of C2+ FE by 3 times is confirmed at the low potential regime where the current density is 60‐140 mA cm‐2, compared to bare OD‐Cu. We report a 45‐h stable CO2RR operation at 220 mA cm‐2, producing a C2+ product FE of ~80%.