High-purity ethylene production via indirect carbon dioxide electrochemical reduction

Abstract High-purity ethylene production from CO 2 electroreduction (CO 2 RR) is a coveted, yet arduous feat because the product stream comprises a blend of unreacted CO 2 , H 2, and other off-target CO 2 reduction products. Here we present an indirect reduction strategy for CO 2 -to-ethylene conversion, one that employs 2-bromoethanol (Br-EO) as a mediator. Br-EO is initially generated from CO 2 RR and subsequently undergoes reduction to ethylene without the need for energy-intensive separation steps. The optimized AC-Ag/C catalyst with Cl incorporation reduces the energy barrier of the debromination step during Br-EO reduction, and accelerates the mass-transfer process, delivering a 4-fold decrease of the relaxation time constant. Resultantly, AC-Ag/C achieved a FE ethylene of over 95.0 ± 0.36% at a low potential of −0.08 V versus reversible hydrogen electrode (RHE) in an H-type cell with 0.5 M KCl electrolyte, alongside a near 100% selectivity within the range of −0.38 to −0.58 V versus RHE. Through this indirect strategy, the average ethylene purity within 6-hour electrolysis was 98.00 ± 1.45 wt%, at −0.48 V (vs RHE) from the neutralized electrolyte after CO 2 reduction over the Cu/Cu 2 O catalyst in a flow-cell.