Charge Polarization Boosting Electrochemical Urea Synthesis by Co-Reduction of CO2 and Nitrite in Dilute Concentrations with a Unity Carbon Selectivity

Abstract

Synthesis of urea through electrocatalytic coupling reaction of CO₂ with nitrite (NO₂⁻) represents a sustainable means to substitute the conventional energy-intensive urea synthetic protocol. The direct conversion of dilute NO₂⁻ in real wastewaters to urea with high efficiency is still a significant challenge, as C-intermediates tend to go through an extensive reduction achieving mostly C-containing productions due to the lack of N-intermediates, originating from slow diffusion rate of NO₂⁻. Herein, we report the charge-polarized Fe^δ−-Cu^δ+ dual sites in metal/carbon heterojunction material (Cu@Fe−N−C) for co-reduction of CO₂ and dilute NO₂⁻ solution (100 ppm NO₂⁻-N). The electron-rich single Fe atoms dispersed N-doped carbon (Fe−N−C) restrain *CO desorption, and the electron-deficient Cu nanoparticles (Cu) promote the deep reduction of NO₂⁻ to *NH₂. As a result, the obtained Cu@Fe−N−C exhibits a high Faradaic efficiency for urea of 50.05 % with a yield of 850.57 mg h⁻¹ g⁻¹ at −0.35 V (vs. RHE) in a flow cell. Moreover, C_{urea-selectivity} reaches to 100 % and a near-unity selectivity for the value-added urea and NH₃ is realized. The present results provide a valuable reference for the design of new catalysts for efficient synthesis of C−N compounds in dilute NO₂⁻ solution.