Localized Alkaline Environment via In Situ Electrostatic Confinement for Enhanced CO2-to-Ethylene Conversion in Neutral Medium

Electrocatalytic CO2 reduction reaction (CO2RR) is one of the most promising routes to facilitate carbon neutrality. An alkaline electrolyte is typically needed to promote the production of valuable multi-carbon molecules (such as ethylene). However, the reaction between CO2 and OH- consumes a significant quantity of CO2/alkali and causes the rapid decay of CO2RR selectivity and stability. Here, we design a catalyst-electrolyte interface with an effective electrostatic confinement of in situ generated OH- to improve ethylene electrosynthesis from CO2 in neutral medium. In situ Raman measurements indicate the direct correlation between ethylene selectivity and the intensities of surface Cu-CO and Cu-OH species, suggesting the promoted C-C coupling with the surface enrichment of OH-. Thus, we report a CO2-to-ethylene Faradaic efficiency (FE) of 70% and a partial current density of 350 mA cm-2 at -0.89 V vs the reversible hydrogen electrode. Furthermore, the system demonstrated a 50 h stable operation at 300 mA cm-2 with an average ethylene FE of ∼68%. This study offers a universal strategy to tune the reaction micro-environment, and a significantly improved ethylene FE of 64.5% was obtained even in acidic electrolytes (pH = 2).