Tuning Interfacial Water Dynamics via Gd‐Doped Cu ₂ O for High‐Rate Selective CO ₂ ‐to‐Ethanol Conversion

The electrochemical reduction of CO 2 (CO 2 RR) to liquid fuels, particularly ethanol, is limited by competing ethylene pathways and sluggish proton‐coupled electron transfer (PCET). While conventional catalyst design has predominantly focused on surface binding energies, the critical role of the electrode–electrolyte interface, specifically the structure of interfacial water, remains underexplored. In this study, we aim to address this gap by reporting on a gadolinium (Gd)‐doped Cu 2 O electrocatalyst that utilizes the high oxophilicity of lanthanides to engineer a free water‐rich interfacial microenvironment, enabling high ethanol selectivity. Operating at an industrially relevant 800 mA cm −2 in a flow cell, the catalyst achieves ethanol Faradaic efficiencies of 46.5% and 48.5% in alkaline and neutral electrolytes, respectively. Remarkably, the ethanol partial current density reaches 527.8 mA cm −2 at 1200 mA cm −2 . Operando spectroscopy reveals that Gd dopants disrupt the rigid, ice‐like interfacial hydrogen‐bonding network, enriching non‐coordinated free water. This disordered environment enhances proton availability, facilitating the selective hydrogenation of * OCCO intermediates to ethanol‐forming species (e.g., * OCCOH) while suppressing ethylene generation. These findings establish a direct structure–function correlation between interfacial water dynamics and product selectivity, providing a novel design principle for sustainable fuel synthesis.