High-Rate CO₂ Conversion to Ethylene via Molecularly Enhanced Electrochemical CO₂ Reduction

Electrochemical conversion of CO₂ into value-added fuels and feedstocks is a promising route to realize sustainable energy cycle and carbon neutrality. Continued efforts to achieve effective electrochemical CO₂ reduction reaction (CO₂RR) have resulted in achieving high selectivity for multi-carbon (C₂₊) chemicals such as ethylene (C₂H₄) and ethanol (C₂H₅OH). To improve the productivity of C₂₊ chemicals, it is necessary to promote C-C coupling on the catalyst surface,as well as *CO formation by fast electron transfer even at high current density. However, even in the flow-type cell with a gas diffusion electrode, it still remains as a challenge due to the sluggish *CO formation on the catalyst surface.<br/>In this work, we report the molecularly-enhanced CO₂ mass transport of Cu catalyst for high current density C₂H₄ production. We augmented ascorbic acid (AA) on Cu nanowires (CuNWs) using graphene quantum dots (GQDs) as a mediator to confine AA in heterogeneous electrocatalysts during CO₂RR. AA on CuNW surface enhanced the CO₂conversion rate by promoting proton-coupled electron transfer (PCET) and providing strong hydrogen bonding site. The nanoconfinement effect and immobilization of AA by GQDs enable redox reversibility and high current density CO₂RR. In the CO₂RR of pristine CuNWs, there is less carbon monoxide (CO) formation in the low potential, and this limits the potential range for stable C₂H₄ production. However, Cu NWs modified with nanoconfined AA by GQDs (cAA-CuNWs) exhibited outstanding C₂H₄production rates with Faradaic efficiency (FE) of 60.7% and C₂H₄ partial current density of 539 mA/cm², which is about 2.9-fold higher performance compared to that of pristine CuNWs. <i>In</i><i>-</i><i>situ</i> Raman spectroscopy revealed that higher population of *CO is covering cAA-CuNW surface by Cu-CO rotation and stretch peak intensity. Also, appropriate ratio of atop bound CO and bridge bound CO has proven the efficient C-C coupling of cAA on CuNW. Grand-canonical density functional theory (GC-DFT) verified that multiple hydrogen bonding sites of AA can effectively control the electronic distributions of water molecules surrounding CO₂, thereby improving *CO formation on the Cu surface. This offers the potential for harnessing AA as a promoter to enhance CO₂ mass transport toward high rate CO₂ to value-added C₂₊ chemical conversion.