Discovery of Ag as an Active and Selective Catalyst for the Electrochemical Synthesis of Urea from NO3- and CO2 with ~100 % Selectivity at -100 mA/cm2 Urea Current Density

The current method to synthesize urea is highly energy intensive and has a massive carbon footprint. Electrochemical synthesis of urea from NO3- and CO2 is an attractive and sustainable way as renewable energy can be used to synthesize green urea at ambient conditions by utilizing the waste NO3- and CO2 from the air or flue gas. In this work, we conduct a thorough catalytic screening on various metal-based catalysts. ~100 % urea Faradaic efficiency and ~-100 mA/cm2 of urea current density is observed at -1.2 V vs. RHE when Ag GDE is used. FTIR analysis further confirms the formation of urea and the presence of *CO intermediates. The excellent kinetics and selectivity towards urea on Ag are explained by a combination of facile first and second C-N bond formation steps and an endergonic (ΔG > 1.5 eV) formamide (HCONH2) formation step from *CONH2 from our DFT studies.