Activation of C₂H₄ reaction pathways in electrochemical CO₂ reduction under low CO₂ partial pressure

Selective conversion of CO₂ to fuels and chemicals has been considered one of the key challenges in the electrochemical CO₂ reduction reaction (CO₂RR). Here, we demonstrate the reaction pathways for CO and C₂H₄ formation on Cu can be regulated by supplying different CO₂ partial pressures. Although it is believed high concentration of surface bound CO is required for C₂H₄ formation, we show excessive supply of CO₂ interferes with C–C coupling and suppress C₂H₄ reaction pathways. This indicates C₂H₄ reaction pathways are limited by the surface recombination of surface bound CO and hydrogen, and the kinetics is affected by adsorbate-adsorbate interactions and/or by physical blocking of active sites on Cu with excess CO₂. Through systematic study, we demonstrate a dilute CO₂ stream selectively activates C₂H₄ formation with significant reduction of the overpotentials (∼ 400 mV) to achieve ∼50% C₂H₄ Faradaic efficiency and enhancement in the C₂H₄ current density (∼50 mA cm⁻²).