Zinc Oxide Nanowires on Copper Foam for Sustainable Urea Electrosynthesis via Co-reduction of Nitrate and Carbon Dioxide—A Step Towards Energy-Efficient Agriculture

Urea mainly serves as the nitrogen source in agricultural fertilizers to promote plant growth and crop yield. It is also a common feedstock in medicine, textile, adhesive, plastic, and electrofuel industries. Industrial urea production involves the Haber-Bosch process utilizing hydrogen and nitrogen gasses to make ammonia, which is then coupled with carbon dioxide, generating urea after the decomposition of ammonium carbamate under the Bosch-Meiser process. Industrial methods occur in high temperatures and pressures, consuming 2% of global energy and approximately 80% of the world's ammonia. A more sustainable approach to urea production could involve developing an electrochemical synthesis system powered by renewable energy. This work aims to develop suitable, efficient, and high-conductivity electrocatalysts from non-precious metal sources for the green production of urea. In previous works involving bimetallic catalysts for urea production, copper and zinc were especially notable due to their abundance and affordability, which makes them suitable for eventual large-scale applications. The catalysts were prepared using copper foam as the cathodic support that facilitated the growth of zinc oxide nanowires by electrodeposition via Cyclic Voltammetry (CV). To mimic scaled-up conditions, the proof of concept for the co-electroreduction of CO2 and NO3- was set up in an H-type electrolytic cell with bicarbonate and nitrate solutions separated by a bipolar membrane. Monitoring and accessing the performance of the electrocatalysts involved in-situ and ex-situ characterization methods such as Raman spectroscopy, Total Reflection X-ray Fluorescence (TXRF), UV-Vis spectroscopy, Hydrogen Nuclear Magnetic Resonance (H-NMR), CV, and others.