Electrochemical Synthesis of Urea and Ammonia by Boron- and Nitrogen-Enriched Nanoporous Polymeric Material as a Metal-Free Electrocatalyst

Urea, a strategic material, is synthesized electrochemically by utilizing two of the major air and water pollutants, carbon dioxide (CO2) and nitrate (NO3–), respectively, as feedstocks. A Boron (B, c.a. 1.6 wt %) and Nitrogen (N, c.a. 39.5 wt %) enriched nanoporous Polymeric Material, BNPM, synthesized by a fast microwave-assisted method using melamine and benzeneboronic acid, has been used as an efficient electrocatalyst for urea production. Optimized textural properties (specific surface area, SABET of 600 m2 g–1) along with simultaneous enrichment of B and N synergistically led to high catalytic performance, which could be attributed to favorable interactions of NO3– and CO2 molecules with the electrocatalyst. BNPM achieved a high Faradaic Efficiency (FE) of 53.2% with a urea yield rate of 31.0 μg h–1 mg–1 at −0.7 V (vs RHE) in 0.1 M KNO3 solution saturated with CO2. Another strategic material, ammonia, was also formed with an FE of 18.5%; however, at a potential of −0.6 V (vs RHE), keeping all other experimental conditions identical, ammonia was the predominant product with an FE of 39.4% and a corresponding yield rate of 6.0 μg h–1 mg–1. A chronoamperometry test for 12 h indicates stable electrocatalytic activity. A combination of in situ Raman spectroscopy coupled with density functional theory (DFT) validated the formation of various reaction intermediates leading to product formation, while the latter provided information on the role of B and N for effective C–N coupling.