The electrocatalytic reduction of CO₂ presents a promising strategy in addressing environmental and energy crisis. Significant progress has been achieved via CO₂ gas diffusion electrolysis, to react at high selectivity and high rate. However, the gas diffusion layer (GDL) of the gas diffusion electrode (GDE) still suffers from low tolerance and limited active sites. Here, the hydrophobic 1-octadecanethiol molecular was functionalized over the Cu catalyst layer of the GDE, which simultaneously stabilizes the GDL and exposes abundant active solid–liquid–gas three-phase interfaces. The resultant GDE exhibits multi-carbon (C₂₊) product selectivity over faradaic efficiency (FE) of 70.0% in the range of 100 to 800 mA·cm^-2, with the peak FE_C2+ of 85.2% at 800 mA·cm^-2. Notably, the strengthened GDE could continuously drive high-current electrolysis for more than 100 h without flooding. This work opens a new way to improve CO₂ gas diffusion electrolysis via surface molecular engineering.