Bifunctional Gas Diffusion Electrode Enables In Situ Separation and Conversion of CO2 to Ethylene from Dilute Stream

The requirement of concentrated carbon dioxide (CO2 ) feedstock significantly limits the economic feasibility of electrochemical CO2 reduction (eCO2 R) which often involves multiple intermediate processes, including CO2 capture, energy-intensive regeneration, compression, and transportation. Herein, a bifunctional gas diffusion electrode (BGDE) for separation and eCO2 R from a low-concentration CO2 stream is reported. The BGDE is demonstrated for the selective production of ethylene (C2 H4 ) by combining high-density-polyethylene-derived porous carbon (HPC) as a physisorbent with polycrystalline copper as a conversion catalyst. The BGDE shows substantial tolerance to 10 vol% CO2 exhibiting a Faradaic efficiency of ≈45% toward C2 H4 at a current density of 80 mA cm-2 , outperforming previous reports that utilized such partial pressure (PCO2 = 0.1 atm and above) and unaltered polycrystalline copper. Molecular dynamics simulation and mixed gas permeability assessment reveal that such selective performance is ensured by high CO2 uptake of the microporous HPC as well as continuous desorption owing to the molecular diffusion and concentration gradient created by the binary flow of CO2 and nitrogen (CO2 |N2 ) within the sorbent boundary. Based on detailed techno-economic analysis, it is concluded that this in situ process can be economically compelling by precluding the C2 H4 production cost associated with the energy-intensive intermediate steps of the conventional decoupled process.