Engineering Copper‐Based Covalent Organic Framework Microenvironments to Enable Efficient CO2 Electroreduction with Tunable Ethylene/Methane Switch

A microenvironment engineering strategy has been developed to switch the CO2 electroreduction reaction (CO2RR) selectivity from methane (CH4) to ethylene (C2H4) by adjusting the coordination microstructures of trinuclear copper cluster‐based metal‐covalent organic framework (MCOF). When Cu sites are oriented to channels in Cu‐PyCA‐MCOF, methane is the main product. Conversely, when trinuclear copper sites are coordinated with OH− and H2O molecules in Cu‐PyCAOH‐MCOF nanosheets, the main product switches from CH4 to C2H4 with 50.5% selectivity and 200.2 mA cm− partial current density at −1.2 V (vs RHE). This happens because CO2 molecules can only contact active sites perpendicular to the trinuclear copper cluster plane in Cu‐PyCAOH‐MCOF nanosheets, where the Cu─Cu distance between them is 3.2 Å, favoring the efficient conversion of CO2 to C2H4 through the C─C coupling reaction. Operando infrared spectroscopy, in situ X‐ray absorption near‐edge structure spectra, and DFT calculations reveal that changing the coordination environments of MCOFs significantly stabilizes key intermediates and reduces the energies of the CO2RR. This work offers an effective strategy for enhancing CO2RR performance toward C2H4 products by tuning the microenvironments of copper‐based electrocatalysts. A microenvironment engineering strategy switches the selectivity of CO2 electroreduction reaction (CO2RR) from methane (CH4) to ethylene (C2H4) by tuning the coordination microstructures of a trinuclear copper cluster‐based metal‐covalent organic framework (MCOF). In Cu‐PyCAOH‐MCOF, oxygen species coordination can alter charge density distribution, lower *COOH formation energy, and influence CO2 attack direction, promoting efficient C─C coupling and CO2 conversion to C2H4.