Cationic covalent framework microenvironment steering CuPt alloy toward record-breaking photoelectrochemical ethane synthesis from CO2

Photoelectrochemical CO2 reduction to multi-carbon products fuels remains challenged by inefficient C–C coupling and competing proton reduction reaction. Herein, we designed a cationic covalent organic framework (COF+) to create an electrostatic microenvironment that synergizes with CuPt alloy nanoparticles for selective ethylene/ethane production. By spatially decoupling CO2 enrichment from proton exclusion, the COF+/CuPt interface simultaneously facilitates CO2 accessibility while impeding H+ migration, suppressing the hydrogen evolution reaction (HER). This unique microenvironment stabilizes key anionic intermediates (*COO−, *OCCO−) and promotes *CO dimerization, steering electron transfer toward C–C coupling. The optimized system achieves a record-high Faradaic efficiency of 51.5 %±5.3 % for ethane and 10.6 %±2.5 % for ethylene with a total C2+ yield exceeding 62 % at −0.25 V vs. RHE and high stability (>300 min), representing the highest performance for photoelectrochemical CO2 reduction to ethane. The combined analyses of in situ spectroscopy and theoretical calculations reveal that electrostatic field effects lower the energy barrier for *OCCO formation while accelerating hydrogenation kinetics. Therefore, this work demonstrates that microenvironment modification of the active site by cationic covalent organic framework is a versatile strategy for solar-driven CO2 conversion into value-added hydrocarbons.