Constructing a Built-In Electric Field via Polymer Modification to Boost D ₂ O Reorientation and Electron Transfer for Deuteroacetic Acid Electrosynthesis

Electrocatalytic deuteration of trichloroacetic acid (TCAA) with D₂O is a promising strategy for the synthesis of acetic-<i>d</i>₃ acid-d (AA-<i>d</i>₄), but its efficiency is limited by high overpotentials caused by sluggish multiproton/electron transfer kinetics and difficult cleavage of the C-Cl bond. Here, a polypyrrole-modified copper electrocatalyst (Cu@PPy) with a strong built-in electric field (BEF) is designed, effectively reducing the overpotential by 100 mV for the high-selectivity electrosynthesis of AA-<i>d</i>₄ with a 94% FE, outperforming pure Cu. The strong BEF at the Cu/PPy interface facilitates the migration of K·D₂O to the electrode surface and promotes the reorientation of the interfacial D₂O into a D-down configuration, thereby promoting the dissociation of D₂O to supply *D for subsequent TCAA deuteration. Moreover, the enhanced adsorption and accelerated electron transfer arising from the electric field promote C-Cl bond activation, thus improving the dechlorination and deuteration kinetics. This strategy enables scale-up electrosynthesis of AA-<i>d</i>₄ at 2.5 A with a high FE of 85%, operating at a lower cell voltage of 2.25 V, highlighting its potential.