Ampere-level CO₂ electroreduction with single-pass conversion exceeding 85% in acid over silver penetration...

Synthesis of valuable chemicals from CO₂ electroreduction in acidic media is highly desirable to overcome carbonation. However, suppressing the hydrogen evolution reaction in such proton-rich environments remains a considerable challenge. The current study demonstrates the use of a hollow fiber silver penetration electrode with hierarchical micro/nanostructures to enable CO₂ reduction to CO in strong acids via balanced coordination of CO₂ and K⁺/H⁺ supplies. Correspondingly, a CO faradaic efficiency of 95% is achieved at a partial current density as high as 4.3 A/cm² in a pH = 1 solution of H₂SO₄ and KCl, sustaining 200 h of continuous electrolysis at a current density of 2 A/cm² with over 85% single-pass conversion of CO₂. The experimental results and density functional theory calculations suggest that the controllable CO₂ feeding induced by the hollow fiber penetration configuration primarily coordinate the CO₂/H⁺ balance on Ag active sites in strong acids, favoring CO₂ activation and key intermediate *COOH formation, resulting in enhanced CO formation.