HEDP‐Modified Cu ₂ O Catalyst Enables Efficient C ₂₊ Product Formation in Acidic CO ₂ Electroreduction

ABSTRACT Efficient electrocatalytic CO 2 reduction (ECR) to multi‐carbon (C 2+ ) products under acidic conditions requires suppression of the competing hydrogen evolution reaction, which can be achieved with high concentrations of potassium ions (K + ) dissolved in the electrolyte. However, this excess of salt ions generates unwanted byproducts, negating the advantage of efficiency over extended use. Herein, we demonstrate a strategy to modify Cu 2 O with hydroxyethanediphosphonic acid (HEDP) to induce a high K + microenvironment, thereby enabling efficient CO 2 conversion to C 2+ products, even at low K + concentrations. In a 3.0 M K + electrolyte (pH 1.0), a faradaic efficiency (FE) of 79.3% for C 2+ products was achieved at a current density of −700 mA cm −2 . Notably, after activation in a K + ‐containing electrolyte, the FE for C 2+ products can still reach 50% even in a K + ‐free electrolyte (1 m M H 2 SO 4 ), while the FE for H 2 remains below 15%. Experimental and first‐principles calculations revealed that HEDP facilitated K + enrichment on the catalyst interface, induced a higher local pH microenvironment, and promoted C−C coupling. Our interfacial microenvironment optimization strategy harnesses the critical role of the electrode‐electrolyte interface in promoting efficient CO 2 electroreduction to C 2+ products under acidic conditions with low K + concentrations.