A Universal Approach for Sustainable Urea Synthesis via Intermediate Assembly at the Electrode/Electrolyte Interface

Abstract

Electrocatalytic C−N coupling process is indeed a sustainable alternative for direct urea synthesis and co‐upgrading of carbon dioxide and nitrate wastes. However, the main challenge lies in the unactivated C−N coupling process. Here, we proposed a strategy of intermediate assembly with alkali metal cations to activate C−N coupling at the electrode/electrolyte interface. Urea synthesis activity follows the trend of Li+<Na+<Cs+<K+. In the presence of K+, a world‐record performance was achieved with a urea yield rate of 212.8±10.6 mmol h−1 g−1 on a single‐atom Co supported TiO2 catalyst at −0.80 V versus reversible hydrogen electrode. Theoretical calculations and operando synchrotron‐radiation Fourier transform infrared measurements revealed that the energy barriers of C−N coupling were significantly decreased via K+ mediated intermediate assembly. By applying this strategy to various catalysts, we demonstrate that intermediate assembly at the electrode/electrolyte interface is a universal approach to boost sustainable urea synthesis.

Selective Electrosynthesis of Urea via C−N Coupling: Current Status, Challenges and Future Prospects

“…À 1 59.7 � 3.4 % Co 1 À TiO 2 [38] 1 bar CO 2 0.1 M KNO 3 0.9 M KHCO 3 + 0.1 M KNO 3 À 0.8 V 212.8 � 10.6 mmol h À 1 g À 1 36.2 % CuWO 4 [29] 1 bar CO 2 0.1 M KNO 3 0.1 M KNO 3 À 0.2 V 98 � 3.2 μg h À 1 mg À 1 cat 70.1 � 2.4 % Bi: 10 % In/C [25] 1 bar CO 2 0.1 M KNO 3 0.1 M KHCO 3 À 0.45 V 606.38 μg mg À 1 h À 1 20.31 % Cu 97 In 3 À C [30] 1 bar CO 2 10 mM KNO 3 0.1 M KHCO 3 + 10 mM KNO 3 À 1.4 V 13.1 mmol g À 1 h À 1 -MoO x /C [37] 1 bar CO 2 0.1 M KNO 3 0.1 M KNO 3 À 0.6 V 1431.5 μg h À 1 mg cat À 1 27.7 % Cu 1 À CeO 2 [33] 1 bar CO 2 50 mM KNO 3 0.1 M KHCO 3 + 50 mM KNO 3 À 1.6 V 52.84 mmol h À 1 g cat À 1 -CoRuN 6 [34] 1 bar CO 2 0.1 M KNO3 0.1 M KNO 3 À 0.6 V 8.98 mmol h À 1 g À 1 25.31 % CuÀ SPÀ OMe [36] 1 bar CO 2 0.01 M KNO 3 0.1 M KHCO 3 + 0.01 M KNO 3 À 0.49 V 3.64 mg h À 1 mg cat…”

“…The K + mediated intermediate assembly strategy significantly reduced the CÀ N coupling energy barrier to promote electrocatalytic urea synthesis (Figure 7). [38] In a word, these regulation strategies, such as additives, doping, bimetallic sites, defects engineering, regulating crystal face or surface sites and functional nanoclusters, could obviously improve the efficiency of urea electrosynthesis from CO 2 and NO 3 À or NO 2 À via CÀ N coupling. This approach enables richnitrogen waste a great opportunity to "turn waste into treasure", meanwhile may alleviate energy, resources and environmental problems.…”

“…c) Urea yield rates at À 1.50 V versus RHE for TiO 2 , mÀ Cu 2 O, CuÀ CeO 2 , VoÀ CeO 2 , Cu 97 In 3 À C and BÀ FeNiÀ DASC with 0.2 M and 1.0 M of K + respectively. d) Schematic diagram of K + -participated urea synthesis path [38]. Copyright 2023, Wiley.…”

Catalysts for C–N coupling in urea electrosynthesis under ambient conditions from carbon dioxide and nitrogenous species

“…The cation effect has the potential to control the key intermediate at the electrode/electrolyte interfaces to promote urea synthesis activities. 106 The alkaline metal cations in electrolytes can stabilize intermediates to promote the C–N coupling process, following a sequence of Li + < Na + < Cs + < K + . Besides, the slow gas diffusion at the three-phase interfaces will result in sluggish kinetics, which strongly hinders the whole reaction.…”

Electrochemically nitrate remediation by single-atom catalysts: advances, mechanisms, and prospects

“…For instance, the explicit water layer and implicit solvation can be an effective strategy for treating solvation in the modeling system. Wang et al proposed a hybrid model (containing explicit water layer and implicit solvation) to simulate NITRR at the water/Cu interface [105] . By introducing fractional charges, the pH values on the water/Cu interface can be implicitly controlled.…”