The electrocatalytic reduction of CO2 (CO2RR) presents a viable approach to reduce CO2 emissions and generate valuable chemicals. However, selectivity toward highly valuable C2+ products is still insufficient for practical applications. Herein, we propose an efficient tandem catalytic strategy to polish up the performance of C2+ products via adjacent distinct catalytic sites. The tandem electrocatalyst Cu/NiPc-COF is constructed by uniformly dispersing atomically precise copper nanoclusters [Cu32(PET)24H8Cl2](PPh4)2 (PET = 2-phenylethanethiolate), denoted as Cu32 NCs, on the two-dimensionally conductive Ni-phthalocyanine-based covalent organic framework (NiPc-COF). A high selectivity of 57.1% for C2+ products (C2H4, CH3COOH, and C2H5OH) and a total current density of 353.3 mA cm-2 is reached at -1.6 V in aqueous electrolyte, which surpasses the corresponding Cu32 NCs (FEC2+ = 24.4%, jtotal = 250.1 mA cm-2, -1.6 V) and some other electrocatalysts. Operando experiments and DFT calculations show that locally high *CO concentrations from NiPc-COF sites cause a massive *CO spillover to Cu32 NCs. This enriches *CO coverage, boosting the selectivity of C2+. The work provides an effective approach for designing tandem electrocatalysts that achieve high selectivity to C2+.
Keywords: CO2 electrocatalysis; atomically precise copper nanoclusters; covalent-organic framework; ethylene; tandem catalysis.