(581b) Formation of Carbon-Nitrogen Bonds in Carbon Monoxide Electroreduction (invited)

Authors: 
Jiao, F., University of Delaware
Electrochemical conversion of carbon dioxide (CO2) using renewable electricity is an attractive means for sustainable production of fuels and chemicals. Copper (Cu) has a unique capability of catalyzing carbon-carbon (C-C) bond formation to form high-value multi-carbon (C2+) products. While highly alkaline electrolytes are often used to enhance C2+ selectivity, the inevitable reaction of hydroxide ions with CO2 to form undesired carbonates at the electrode-electrolyte interface disrupts the electrolysis process. This fundamental challenge can be solved by decoupling the CO2 electrolysis into a two-step process, where CO2 is first electrochemically reduced to carbon monoxide (CO) at neutral conditions, followed by CO electroreduction to produce C2+ chemicals in alkaline environments. Nonetheless, only four major C2+ products, i.e., ethylene, acetate, ethanol, and n-propanol, have been reported for CO2/CO electrolysis in aqueous electrolytes.

In this talk, we will present a new study to expand beyond this limited range of simple C-C coupling by demonstrating electrochemical production of acetamide with nearly 40% Faradaic efficiency at a current density of 300 mA/cm2, where the carbon-nitrogen (C-N) bond is formed through CO electroreduction in the presence of ammonia. Full solvent quantum mechanical calculations showed earlier that the under neutral or basic conditions the reaction mechanism involves CO dimerization and sequential transfer of H from two surface water to form the (HO)C*-C*OH intermediate that subsequently leads through two separate pathways to form C2H4 (90%) and ethanol (10%). We show now that (HO)C*-C*OH is also hydrolyzed to *C=C=O, which in turn reacts with NH3 to form intermediates leading to acetamide while suppressing formation of other C2 products. We also successfully extended the range of C-N containing products to N-methylacetamide, N-ethylacetamide, N,N-dimethylacetamide, acetic monoethanolamide, and aceturic acid. Our results provide useful mechanistic insights into Cu-catalyzed CO2/CO electroreduction and demonstrate the construction of carbon-heteroatom bonds in CO2/CO electrolysis. This largely expands the scope of electrocatalytic CO2 utilization pathways for sustainable chemical production.