Tensile‐Strained Cu Penetration Electrode Boosts Asymmetric C–C Coupling for Ampere‐Level CO2‐to‐C2+ Reduction in Acid

The synthesis of multicarbon (C 2+ ) products remains a substantial challenge in sustainable CO 2 electroreduction owing to the need for sufficient current density and faradaic efficiency alongside carbon efficiency. Herein, we demonstrate ampere‐level high‐efficiency CO 2 electroreduction to C 2+ products in both neutral and strongly acidic (pH=1) electrolytes using a hierarchical Cu hollow‐fiber penetration electrode (HPE). High concentration of K + could concurrently suppress hydrogen evolution reaction and facilitate C−C coupling, thereby promoting C 2+ production in strong acid. By optimizing the K + and H + concentration and CO 2 flow rate, a faradaic efficiency of 84.5 % and a partial current density as high as 3.1 A cm −2 for C 2+ products, alongside a single‐pass carbon efficiency of 81.5 % and stable electrolysis for 240 h were demonstrated in a strong acidic solution of H 2 SO 4 and KCl (pH=1). Experimental measurements and density functional theory simulations suggested that tensile‐strained Cu HPE enhances the asymmetric C−C coupling to steer the selectivity and activity of C 2+ products.