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 D 2 O is a promising strategy for the synthesis of acetic- d 3 acid-d (AA- d 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- d 4 with a 94% FE, outperforming pure Cu. The strong BEF at the Cu/PPy interface facilitates the migration of K·D 2 O to the electrode surface and promotes the reorientation of the interfacial D 2 O into a D-down configuration, thereby promoting the dissociation of D 2 O 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- d 4 at 2.5 A with a high FE of 85%, operating at a lower cell voltage of 2.25 V, highlighting its potential.