Asymmetric Cu-N₁O₃ Sites Coupling Atop-type and Bridge-type Adsorbed *C₁ for Electrocatalytic CO₂-to-C₂ Conversion

2D functional porous frameworks offer a platform for studying the structure-activity relationships during electrocatalytic CO₂ reduction reaction (CO₂RR). Yet challenges still exist to breakthrough key limitations on site configuration (typical M-O₄ or M-N₄ units) and product selectivity (common CO₂-to-CO conversion). Herein, a novel 2D metal-organic framework (MOF) with planar asymmetric N/O mixed coordinated Cu-N₁O₃ unit is constructed, labeled as BIT-119. When applied to CO₂RR, BIT-119 could reach a CO₂-to-C₂ conversion with C₂ partial current density ranging from 36.9 to 165.0 mA cm^-2 in flow cell. Compared to the typical symmetric Cu-O₄ units, asymmetric Cu-N₁O₃ 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-N₁O₃ sites could simultaneously couple the atop-type (on Cu site) and bridge-type (on Cu-N site) adsorption of *C₁ species to reach the CO₂-to-C₂ conversion. This work broadens the feasible C-C coupling mechanism on 2D functional porous frameworks.