Tailoring dual-hydrophobic microenvironment for tandem CO₂/CO feedstock to enhance CO₂ electroreduction on Cu-based catalysts

Achieving high selectivity for value-added products in the electrochemical reduction of CO₂ remains challenging due to severe hydrogen evolution, sluggish CO₂ mass transport and low *CO coverage. Herein, we integrate aerophilic SiO₂ and polymer-functionalized copper nanoparticles (Cu-poly) to construct a hierarchical-hydrophobic Cu-poly/SiO₂ composite, which limits the accessibility of H₂O, improves the local concentration of CO₂ and enhances the dimerization of *CO-*CO. Comprehensive investigation using X-ray absorption spectroscopy, <i>in situ</i> infrared spectroscopy and molecular dynamics simulations indicates that the polymer and SiO₂ elevate the oxidation state of Cu species, enhance the CO₂ diffusion coefficients (from 5.27 × 10^-7 on Cu to 8.81 × 10^-7 cm² s^-1 on Cu-poly/SiO₂) and enrich the local *CO concentration. The Cu-poly/SiO₂ electrode delivers an enhanced faradaic efficiency of 60.54% for C₂₊ products, compared to 46.1% of Cu at 600 mA cm^-2. Notably, a high FE of 36.91% and partial current density of 221.46 mA cm^-2 are achieved for C₂H₄ generation in membrane electrode assembly devices adopting an aqueous bicarbonate electrolyte. This work provides a valuable insight into designing catalytic microenvironments of electrocatalysts for enhancing carbonaceous products by facilitating the co-electrolysis of CO₂ and <i>in situ</i>-generated *CO.