Asymmetric Cu-NO Sites Coupling Atop-type and Bridge-type Adsorbed *C for Electrocatalytic CO-to-C Conversion.

2D functional porous frameworks offer a platform for studying the structure-activity relationships during electrocatalytic CO reduction reaction (CORR). Yet challenges still exist to breakthrough key limitations on site configuration (typical M-O or M-N units) and product selectivity (common CO-to-CO conversion). Herein, a novel 2D metal-organic framework (MOF) with planar asymmetric N/O mixed coordinated Cu-NO unit is constructed, labeled as BIT-119. When applied to CORR, BIT-119 could reach a CO-to-C conversion with C partial current density ranging from 36.9 to 165.0 mA cm in flow cell. Compared to the typical symmetric Cu-O units, asymmetric Cu-NO units lead to the re-distribution of local electron structure, regulating the adsorption strength of several key adsorbates and the following catalytic selectivity. From experimental and theoretical analyses, Cu-NO sites could simultaneously couple the atop-type (on Cu site) and bridge-type (on Cu-N site) adsorption of *C species to reach the CO-to-C conversion. This work broadens the feasible C-C coupling mechanism on 2D functional porous frameworks.