HEDP-Modified Cu₂O Catalyst Enables Efficient C₂₊ Product Formation in Acidic CO₂ Electroreduction

Efficient electrocatalytic CO₂ reduction (ECR) to multi-carbon (C₂₊) 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 Cu₂O with hydroxyethanediphosphonic acid (HEDP) to induce a high K⁺ microenvironment, thereby enabling efficient CO₂ conversion to C₂₊ products, even at low K⁺ concentrations. In a 3.0 M K⁺ electrolyte (pH 1.0), a faradaic efficiency (FE) of 79.3% for C₂₊ products was achieved at a current density of −700 mA cm⁻². Notably, after activation in a K⁺-containing electrolyte, the FE for C₂₊ products can still reach 50% even in a K⁺-free electrolyte (1 mM H₂SO₄), while the FE for H₂ 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 CO₂ electroreduction to C₂₊ products under acidic conditions with low K⁺ concentrations.