Selective CO2 electroreduction to multicarbon products exceeding 2 A cm−2 in strong acids via a hollow-fiber Cu penetration electrode†

CO₂ electroreduction in acidic media is highly attractive to avoid carbonation loss, but remains a challenge for selective reduction of CO₂ due to overwhelming hydrogen evolution reaction (HER) in a proton-rich environment. Herein, we report a hollow-fiber Cu penetration electrode that can effectively inhibit the HER while promoting CO₂ reduction kinetics and even C–C coupling to form multicarbon (C₂₊) products in strong acids. A faradaic efficiency of 73.4%, a partial current density of 2.2 A cm⁻², and a single pass carbon efficiency of 51.8% were achieved for C₂₊ production, sustaining 100 h electrolysis in a pH = 0.71 solution of H₂SO₄ and KCl. Sufficient CO₂ feeding induced by the hollow-fiber penetration configuration greatly improved CO₂ coverage on Cu active sites in strong acids, favoring CO₂ activation, *CHO and *CO formation, and their couplings to C₂₊ products.