Interfacial Diffusion-Reaction Coupling Strategy for CO₂ Reduction on Copper Surface in Acidic Medium

CO₂ electroreduction reaction in acid medium to produce multicarbon (C₂₊) products has gained attention as an alternative to the traditional processes in neutral or alkaline solutions which often suffer from low single-pass conversion efficiency due to (bi)carbonate accumulation at the cathode. However, the CO₂ conversion efficiency in acid remains unsatisfactory. Herein, a strong-polarized layer-covered Cu catalyst is developed as electrode for CO₂ reduction reaction (CO₂RR) in acid. Such a strong dipole moment layer is a sp³-hybridized nitrogen (sp³-N)-enriched azulene-based polymer, which acts as Lewis base to boost the CO₂-diffusion kinetics in inner Helmholtz plane. Such unique electrode delivers nearly 84% C₂ Faradaic efficiency at 200 mA cm^-2, and demonstrates long-term stability over 40 h, which is the record for CO₂RR in acidic media. In situ experiments manifest the moderate azulene-polarized sp³-N-enriched micro-environment can increase the local CO₂/H₂O ratio at electric double-layer to further stabilize the key intermediate atop-bound *CO. Theoretical calculations reveal that the strong-polarized layer decreases the reaction energy barrier for C-C coupling. This study not only uncovers the units with strong dipole moment on tuning sp³-N-enriched micro-environment, but also provides an interfacial diffusion-reaction coupling strategy to enhance the selectivity of CO₂RR by decorating polycrystalline Cu with strong-polarized polymers.