Stabilizing copper sites in coordination polymers toward efficient electrochemical C-C coupling

Electroreduction of carbon dioxide with renewable electricity holds promise for achieving net-zero carbon emissions. Single-site catalysts have been reported to catalyze carbon-carbon (C-C) coupling—the indispensable step for more valuable multi-carbon (C₂₊) products—but were proven to be transformed in situ to metallic agglomerations under working conditions. Here, we report a stable single-site copper coordination polymer (Cu(OH)BTA) with periodic neighboring coppers and it exhibits 1.5 times increase of C₂H₄ selectivity compared to its metallic counterpart at 500 mA cm⁻². In-situ/operando X-ray absorption, Raman, and infrared spectroscopies reveal that the catalyst remains structurally stable and does not undergo a dynamic transformation during reaction. Electrochemical and kinetic isotope effect analyses together with computational calculations show that neighboring Cu in the polymer provides suitably-distanced dual sites that enable the energetically favorable formation of an *OCCHO intermediate post a rate-determining step of CO hydrogenation. Accommodation of this intermediate imposes little changes of conformational energy to the catalyst structure during the C-C coupling. We stably operate full-device CO₂ electrolysis at an industry-relevant current of one ampere for 67 h in a membrane electrode assembly. The coordination polymers provide a perspective on designing molecularly stable, single-site catalysts for electrochemical CO₂ conversion.