Screening transition metal electrodes for achieving near 100% selectivity to urea via electroreduction of NO3− and CO2 at 100 mA cm−2 current density

Abstract

The current method to synthesize urea is highly energy-intensive and has a massive carbon footprint. The electrochemical synthesis of urea from NO₃⁻ and CO₂ is an attractive and sustainable approach, as renewable energy can be used to synthesize green urea under ambient conditions by utilizing waste NO₃⁻ and CO₂ from the air or flue gas. In this work, we conducted a thorough catalytic screening of various metal-based catalysts. When the Ag GDE was used as a working electrode, ∼100% urea faradaic efficiency and ∼−100 mA cm⁻² of urea current density were observed at −1.2 V vs. RHE. FTIR analysis further confirmed the formation of urea and the presence of *CO intermediates. Through DFT studies, excellent kinetics and selectivity toward urea on Ag were explained by a combination of the facile first and second C–N bond-formation steps and an endergonic (ΔG > 1.5 eV) formamide (HCONH₂) formation from *CONH₂ step.