Covalent Elaboration of Confined Surfaces Steers C─C Coupling Pathway for Selective Electrochemical CO ₂ Reduction at Ampere‐Level

Microenvironmental engineering of electrocatalysts is pivotal for directing reaction pathways and stabilizing key intermediates in CO₂ reduction reaction (CO₂RR) to multicarbon products, but it has yet to meet the industrial requirement for selectively producing a most desired product, such as ethylene or ethanol, at a steady above-ampere current level. Herein, a topotactic conversion cum covalent functionalization strategy is invoked to craft a catalyst with confined and modulated surfaces that can bias the reaction heavily for ethylene production with a 22-fold boost in the ethylene/ethanol ratio. The well-tuned covalent structural motif of ─Si─O─Cu─ on PDMS-Cu₂O/C dramatically elevates the C₂H₄-forming activity with a faradaic efficiency reaching up to 71% and a high partial current density of 513.6 mA cm^-2. Operando infrared spectroscopy and density functional theory calculations unveil the ultralow coordination number and the upshifted d-band center. Notably, modulating the d-band center with the covalently elaborated surfaces allows control of the adsorption energies of CHO* and other intermediates along the ethylene path, largely lowering energy barriers for the key steps, particularly the formation of CH₂CHO*. This work sheds light on the microenvironment modulation at the surface bonding to mesoscopic scales to precisely control catalytic processes and steer reaction pathways toward the target product.