Molecular cages synchronise *CO retention and Cu⁺ stabilisation for acidic ethylene electrosynthesis

Selective CO₂-to-ethylene conversion in acidic electrolytes requires catalysts that can sustain reactive carbon intermediates and maintain active copper states under demanding operating conditions. A surfactant-based molecular cage addresses these coupled challenges by confining CO intermediates near the copper surface while stabilising Cu⁺ species that promote carbon–carbon coupling. This coordinated interfacial control delivers ethylene Faradaic efficiencies above 60% at current densities of 300–1100 mA cm⁻², alongside stable operation exceeding 195 h at an ethylene selectivity of approximately 50%. Beyond these performance gains, this study advances a broader catalyst design principle: controlling residence time of intermediates remain near active sites is as consequential as preserving the active sites themselves. Integrating intermediate confinement with oxidation-state stabilisation offers a promising route toward selective and durable acidic CO₂ electrolysis.