(710e) Electrochemical Synthesis of Urea By the Co-Reduction of Nitrates and CO2 on Co-Cu Bimetallic Gas Diffusion Electrodes (GDE)

Industrial manufacturing of chemicals and commodities have a large carbon footprint and electrification of the chemical processes using renewable electricity is desired. NH₃ is the second largest produced chemical in the world, and it is responsible for 1 to 2 % of the total greenhouse gas emissions. NH₃ is manufactured by Haber-Bosch process which requires a high temperature of 400 to 500 °C and a high pressure of 150 to 200 atm. NH₃ is majorly used to make fertilizers and urea is one of the important fertilizers. Urea is manufactured in an industrial scale by using Bosch-Meiser process and it is energy intensive involving a high temperature of 160 °C and a high pressure of 110 atm. The overall synthesis of urea involves a large amount of greenhouse gas emissions and hence electrification of this process is required. Here it is presumed that nitrates come from treated wastewater or electrochemical oxidation of N₂. Co-Cu bimetallic catalyst is used as the electrocatalyst, and 1 M KNO₃ and 1 M KHCO₃ sparged with CO₂ is used as the electrolyte. The Co and Cu fractions are varied to get a high urea Faradaic efficiency. The catalyst is characterized using XRD, XPS, SEM, and EDS. We achieved a very high urea Faradaic efficiency of ~50 % and a high urea current density of 130 mA/cm² when the Co-Cu bimetallic is used in a gas diffusion electrode (GDE) based reactor. The stability of the catalyst is studied for 24 h and the catalyst remained stable. The effect of operating conditions such as CO₂ flowrate, pH, counter cations, supporting electrolyte anions, and the concentration of the electrolyte are varied and optimized to get the highest urea Faradaic efficiency. The reaction mechanism of the urea formation on Co-Cu bimetallic catalyst is proposed from DFT calculations.