Chlorine-Functionalized Silane-Modified Copper Electrocatalyst for Enhanced CO₂ Reduction to Multi-Carbon Products

Electrochemical CO₂ reduction reaction (CO₂RR) on Cu-based catalysts toward multi-carbon (C₂₊) products remains challenging due to sluggish CO₂ activation, high C-C dimerization energy barriers, and competing hydrogen evolution reaction. While halide species, such as chlorine, promote CO₂ activation, and silane-based modifiers can regulate charge transfer to enhance C-C dimerization, these effects are typically decoupled when applied separately. Herein, we identify 3-chloropropyltrimethoxysilane (CPTMS) as a molecular modifier that integrates halide functionality and silane anchoring within one scaffold, enabling spatially coupled regulation of CO₂RR intermediates at the Cu interface. Introduced via a one-step electrodeposition strategy, the CPTMS-modified Cu catalyst exhibits a 5-fold enhancement in C₂₊ faradaic efficiency, reaching 75% ± 2% compared with 15% ± 4% for unmodified CuO_x at -1.5 V vs. the reverse hydrogen electrode with a partial current density of 105 mA cm^-2. In-situ synchrotron-based Fourier transform infrared reveals that the spatially coupled chlorine and silicon functionalities sequentially optimize the CO₂RR pathway by promoting CO₂ activation, *COOH formation, *CO protonation, and subsequent C-C dimerization on Cu active sites achieving enhanced C₂₊ product formation. This work elucidates molecularly integrated halide-silane functionalization-enabled synergistic interfacial control, offering a rational design strategy for advancing selective C₂₊ product formation in CO₂RR.