Electrochemical Synthesis of Urea‐Ammonium‐Nitrate (UAN) Fertilizer via Dual Reduction of CO ₂ and Nitrate

Abstract

The urea-ammonium-nitrate (UAN) fertilizers are the optimal supply of nutrients, which promotes healthy plants and reduces the need for frequent applications. Using manganese phthalocyanine (MnPc) supported by amine-functionalized graphene (AFG) catalyst via a unique electrochemical method that greatly improves the catalytic performance for the UAN synthesis process. During CO₂ and NO₃ ^- co-reduction (CO₂ + 2NO₃ ^- + 18H⁺ + 16e^- → CO(NH₂)₂ + 7H₂O), the MnPc-AFG catalyst demonstrated the urea production rate of 397.61 µg h^-1 mg_cat ^-1, as well as a 27.06% Faradaic efficiency (FE) at -1.0 V versus RHE. Simultaneously, the yield rate of ammonia synthesis from NO₃ ^- reduction [NO₃ ^- + 9H⁺ + 8e^- → NH₃ + 3H₂O] is 433.95 µg h^-1 mg_cat ^-1 and exhibiting a 52.13% Faradaic efficiency at -1.0 V versus RHE. The electrolyte still contains unreacted nitrate, which raises the possibility of selective UAN production. In situ Fourier transform infrared spectroscopy (FTIR) confirmed the formation of C─N and N─H bonds during electrolysis. Density functional theory (DFT) analysis provided the overall reaction mechanism and free energy profile for the formation of UAN production. This sustainable development opens up new possibilities for the manufacture of electrochemical UAN fertilizers.