Localized Alkaline Environment via In Situ Electrostatic Confinement for Enhanced CO 2 -to-Ethylene Conversion in Neutral Medium.

Electrocatalytic CO 2 reduction reaction (CO 2 RR) 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 CO 2 and OH - consumes a significant quantity of CO 2 /alkali and causes the rapid decay of CO 2 RR 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 CO 2 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 CO 2 -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).