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.