Molecular tuning of CO 2 -to-ethylene conversion

The electrocatalytic carbon dioxide (CO2) reduction reaction (CO2RR) to value-added fuels and feedstocks provides a sustainable and carbon-neutral approach to the storage of intermittent renewable electricity1. The highly selective generation of economically desirable C2 products such as ethylene from CO2RR remains a challenge2. Tuning the stabilities of intermediates to favour a desired reaction pathway offers the opportunity to enhance selectivity3–5, and this has recently been explored on copper (Cu) via control over morphology6, grain boundaries7, facets8, oxidation state9 and dopants10. Unfortunately, the Faradaic efficiency for ethylene is still low in neutral media (60 per cent at a partial current density of 7 mA cm−2 in the best catalyst reported so far9), resulting in a low energy efficiency. Here we present a molecular tuning strategy—the functionalization of the surface of electrocatalysts with organic molecules—that stabilizes intermediates for enhanced CO2RR to ethylene. Using electrochemical, operando/in situ spectroscopic and computational studies, we investigate the influence of a library of molecules, derived via electro-dimerization of arylpyridiniums11, on Cu. We find that the adhered molecules improve the stabilization of an atop-bound CO intermediate, thereby favouring further reduction to ethylene. As a result of this strategy, we report the CO2RR to ethylene with a Faradaic efficiency of 72 per cent at a partial current density of 230 mA cm−2 in a liquid-electrolyte flow cell in neutral medium. We report stable ethylene electrosynthesis for 190 hours in a membrane-electrode-assembly-based system that provides a full-cell energy efficiency of 20 per cent. These findings indicate how molecular strategies can complement heterogeneous catalysts by stabilizing intermediates via local molecular tuning.