Plasma-flow cell electrocatalysis for ambient co-synthesis of urea and ammonia

Abstract

Urea, a pivotal chemical in agriculture and societal advancement, presents a significant obstacle due to its energy-intensive industrial production. In this study, we propose a plasma-flow cell electrocatalysis system for ambient co-synthesis of urea (CO(NH2)2) and ammonia (NH3) from CO2 and air. The plasma efficiently produces more accessible NOx (primarily NO) from air, which is then used for the subsequent electroreduction of NO2− and CO2 into urea and ammonia. To facilitate this process, a nickel-cobalt bimetallic catalyst (NiCo2O4) was synthesized, which exhibited remarkable yields for urea (0.0961 mmol h−1) and ammonia (0.3557 mmol h−1), surpassing those of Co3O4 and Ni(OH)2. Density functional theory (DFT) calculations reveal the strong binding affinity of Ni-O/Co-O bonds in NiCo2O4. Moreover, Gibbs free energy analysis of the urea / ammonia synthesis pathway indicates that NiCo2O4 possesses the lowest energy barrier (ΔG = 0.20 eV/ΔG = 0.66 eV) in the dual synthesis pathway, elucidating its optimized activity in the CN coupling reaction. This study opens up new avenues for a sustainable production of urea and ammonia via plasma-electrocatalysis cascade systems.

Keywords

• Urea
• Ammonia
• Electrocatalysis
• Plasma
• Flow cell