Unveiling the role of nitrate enrichment on electrode surface to achieve high selectivity of electrosynthesis urea of C-N coupling in the flow-through electrolytic cell

Electrochemical carbon dioxide synergistic nitrate for urea synthesis is essential for mitigating greenhouse effects and recycling resources. Limited ion migration in traditional H-type electrolysis cells has led to a growing preference for flow cells to enhance mass transfer, but mechanisms of their impact on synthesis of value-added product urea remain unclear. Herein, this study was devoted to revealing the differences in ion transport among different electrolysis cells and their effect on C-N coupling, providing insights into optimizing urea synthesis. Simulation of the multi-physics fields in flow-through, flow-by, and H-type electrolytic cells systematically investigated these effects. The simulations revealed that the flow-through cell significantly enriched NO 3 − on the cathode surface and within its pore structures under hydrodynamic conditions, facilitating intermediate interactions. Experimental validation using KHCO 3 and KNO 3 demonstrated that the flow-through cell achieved a urea yield of 3182.7 μg h −1 mg cat. −1 and an electricity consumption of 95.7 kWh kg urea −1 . Additionally, the urea Faradaic efficiency reached 24.9 %, which was 12.7 % and 27 % higher than those of the flow-by and H-type cells, respectively, underscoring the superior urea selectivity of the flow-through cell. Mechanistic analysis through electrochemical tests further demonstrated the flow-through cell exhibited a faster reaction rate, enhanced charge transfer, and lower NO 3 − diffusion resistance. These results highlight the critical role of flow-through electrolysis in promoting ion-to-intermediate conversion and suggest that targeted modifications of porous electrodes to enhance NO 3 − enrichment could further improve the efficiency of electrochemical C-N coupling for urea synthesis.