Chlorine‐Functionalized Silane‐Modified Copper Electrocatalyst for Enhanced CO ₂ Reduction to Multi‐Carbon Products

ABSTRACT Electrochemical CO 2 reduction reaction (CO 2 RR) on Cu‐based catalysts toward multi‐carbon (C 2+ ) products remains challenging due to sluggish CO 2 activation, high C–C dimerization energy barriers, and competing hydrogen evolution reaction. While halide species, such as chlorine, promote CO 2 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 CO 2 RR intermediates at the Cu interface. Introduced via a one‐step electrodeposition strategy, the CPTMS‐modified Cu catalyst exhibits a 5‐fold enhancement in C 2+ 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 CO 2 RR pathway by promoting CO 2 activation, *COOH formation, *CO protonation, and subsequent C–C dimerization on Cu active sites achieving enhanced C 2+ product formation. This work elucidates molecularly integrated halide‐silane functionalization‐enabled synergistic interfacial control, offering a rational design strategy for advancing selective C 2+ product formation in CO 2 RR.