Electrochemical CO2 reduction (CO2R) using copper-based (Cu) electrocatalysts is an attractive approach to converting anthropogenic CO2 emissions into value-added products. Among these value-added products are the multi-carbon (C2+) products, such as ethylene and ethanol, which are of particular interest. While most laboratory studies use pure CO2 feedstocks, the costs of separation and purification of CO2 from direct sources (such as flue gas) increase the operational cost and decrease the economic feasibility of the process. Direct usage of flue gas is challenging due to both the relatively low concentration of CO2, and the presence of O2 impurities introducing a competing reaction called the Oxygen Reduction Reaction (ORR). Herein, we demonstrate the ability of films formed from the in-situ reduction of N-tolylpyridinium triflate (tolyl-pyr) and N,N’-ethylene-phenanthrolinium dibromide (1-Br2) to suppress ORR and maintain CO2R selectivity towards multi-carbon products in the presence of O2. We find that both variants of molecular films suppress ORR under both alkaline and acidic electrolytes over a wide range of ratios of CO2:O2. With a 1:1 CO2/O2 ratio, the 1-Br2 derived film reduced the current density towards ORR by a factor over 2.3 under alkaline electrolytes and over 2.5 under acidic electrolytes compared to the case with no film. Further studies revealed that the tolyl-pyr derived film reduces the O2 diffusion coefficient, while the 1-Br2 derived film slowed ORR kinetics. Under a simulated flue gas feedstock (20% CO2, 5% O2, and 75% N2), the 1-Br2 derived film demonstrated a stable ~60% FE toward C2+ products (~50% C2H4) for 6 hours in acidic media, which demonstrates a pathway for direct flue gas utilization.
