(513fs) Electrochemical Synthesis of Urea By Co-Reduction of Nitrates and CO2 on Cu, Zn and Ti Gas Diffusion Electrodes (GDE)

Urea is produced in industries by Bosch-Meiser process from NH₃ and CO₂ which involves a high pressure of 110 atm and a temperature of 160 °C. The precursor, NH₃ is manufactured by Haber-Bosch process which involves, reaction of pure N₂ and H₂ at high pressures between 150 and 200 atm, and high temperatures of 400 to 500 °C. The overall process for making Urea is highly energy intensive and leaves a larger carbon footprint as the H₂ is obtained by steam reforming process.

Here, we propose an electrochemical process to synthesize urea by co-reduction of nitrates and captured CO₂ at ambient conditions. Nitrates are commonly found in the waste streams of industrial uranium processing, ammunition industries (more than 65 %) and also in agricultural run-off water. Nitrates are generally reduced electrochemically to N₂ and other gaseous products. Reducing nitrates into a more useful product, urea will save the energy needed to manufacture urea and ammonia which is a precursor to make urea.

Three different catalysts are studied namely Cu, Zn, and Ti, which are electrodeposited on the porous Gas Diffusion Electrode (GDE). The gaseous products (CO, CH₄, H₂) are quantified by Gas Chromatography (GC) and the liquid products (HCOOH) are quantified by High Performance Liquid Chromatography (HPLC). The main product Urea is quantified using UV-Visible Spectroscopy (Indophenol Method and Nessler’s reagent method) by the enzymatic decomposition of Urea using Urease enzyme. The Faradaic Efficiency and the yield of urea, and other byproducts are measured. The effect of operating conditions such as pH, flow rate of CO₂, concentration of the electrolyte, and the counter cations in the electrolyte are studied and optimized. The stability of the catalyst for an operating period of 24 h is studied.