Interfacial Synergy of Cation Enrichment and Hydrophobicity in Bi₂S₃ Nanoflowers for Efficient Acidic CO₂ Electroreduction

The implementation of acidic CO₂ electroreduction (CO₂RR) is hindered by catalyst corrosion and the parasitic hydrogen evolution reaction (HER). We construct a hydrophobic hexadecyltrimethoxysilane (HDTMS)-modified Bi₂S₃ nanoflower catalyst (Bi₂S₃-C₁₆) synergistically integrating cationic enrichment and interfacial hydrophobicity to achieve stable CO₂-to-HCOOH conversion at pH = 2. COMSOL simulations reveal that the high-curvature architecture amplifies local electric fields, driving K⁺ accumulation to stabilize *OCHO intermediates via dipole interactions. The density functional theory also confirms this, showing a reduced *CO₂→*OCHO energy barrier. In situ ATR-FTIR captures *OCHO vibrational modes (1575 cm^-1) and HCOOH signatures (1695 cm^-1). HDTMS reduces proton accessibility (rotating disc electrode analysis), suppressing HER. Consequently, Bi₂S₃-C₁₆ achieves 89.6% HCOOH Faradaic efficiency at -400 mA cm^-2 with 44.46% cathodic energy efficiency, operating stably for 48 h. This provides a paradigm for interfacial microenvironment control in harsh electrocatalytic systems.