Boosting the Urea Synthesis Rate on Ni Single-Atom Catalysts: The Impact of Acetonitrile Electrolyte in the Tandem CO₂ Reduction/Nucleophilic Addition Reaction

Abstract

The tandem CO 2 reduction reaction (CO 2 RR) process/nucleophilic addition reaction can be an efficient and environmentally friendly method for the synthesis of urea. However, the low stability of the CO 2•− intermediates causes a low yield of urea through the nucleophilic addition reaction. Here, we propose an effective method to improve the yield of nucleophilic addition to synthesize urea on Ni single-atom catalysts (Ni-SACs) by introducing acetonitrile into aqueous electrolytes. A high yield of urea of 1.10 mM•g −1 •h −1 was achieved on the Ni-SACs at −2.2 V (vs saturated calomel electrode) in acetonitrile/ water mixture electrolytes, presenting the best performance for urea synthesis via the nucleophilic addition reaction reported so far. Further studies have shown that the acetonitrile stabilizes the CO 2•− intermediates on the one hand and on the other hand, it lowers the energy barrier of the nucleophilic addition reaction on Ni-SACs through coordination, thus increasing an overall kinetic rate for urea formation.