Tailoring the Catalytic Microenvironment of Cu₂O with SiO₂ to Enhance C₂₊ Product Selectivity in CO₂ Electroreduction

Achieving high activity and selectivity of multicarbon products in the CO₂ reduction reaction (CO₂RR) on Cu-based electrocatalysts remains challenging due to the limited concentration of local OH^–, sluggish CO₂ diffusion, and competitive hydrogen evolution reaction. Herein, we report aerophilic nanocomposites of hydrophobic SiO₂ aerosol and Cu₂O nanocubes to tailor the microenvironment for enhancing CO₂ electroreduction in 0.1 M KHCO₃ aqueous electrolyte. Combined in situ infrared analysis, molecular dynamics simulations, and density functional theory calculations reveal that the composite Cu₂O/SiO₂ enriches the local hydroxyl by blocking the reaction between OH^– and HCO₃^–, accelerates CO₂ diffusion coefficient (from 2.67 × 10^–10 to 8.46 × 10^–10 m² s^–1), and renders a lower dissociation energy of H₂O than bicarbonate (0.49 vs 1.24 eV on Cu₂O (111)) as compared to neat Cu₂O. Consequently, Cu₂O/SiO₂ promotes the formation of C₂₊ products (Faradaic efficiency FE_C2+ from 52.4 to 75.6%) and suppresses hydrogen generation (FE_H2 from 30.0 to 9.6%) at −1.2 V versus reversible hydrogen electrode. The results provide insight into the selectivity improvement of CO₂RR electrocatalysis by regulating the local microenvironment of alkalinity, H₂O transportation, and CO₂ permeability.