Co-activation of CO₂ and N₂ in plasma-electrochemical system for direct urea production from flue gas

Flue gas is the hot exhaust from industrial combustion processes, composed of N₂ with 10–20% CO₂. Capture and conversion of flue gas is an industrially important process, as it results in a direct reduction in greenhouse gases emission. Here we demonstrate a non-thermal plasma reactor with an electrochemical cell to produce urea directly from a simulated flue gas stream (19% CO₂, 80% N₂, 1% O₂). The plasma activates N₂ and CO₂, after gas-liquid capture, delivers a nitrite-dominant catholyte and CO/CO₂-rich gas stream, enabling co-reduction of NO_x and CO₂ to urea in a single step. Benchmarking Cu catalyst shows that CO₂ is a limiting reactant in this process, and thus we design bimetallic catalysts (CuAg/C, CuZn/C, CuRu/C, CuBi/C, CuPd/C) to enhance CO₂ adsorption in the electrochemical reaction. CuAg/C is identified as the most active urea catalyst, achieving a peak rate of 142.6 μmol h⁻¹ g⁻¹ at 10 mA cm⁻², followed by CuZn/C. In situ Raman confirms a higher concentration of atop-CO (≈1996 and 2077 cm⁻¹) on CuAg/C under reaction conditions, than that of the control Cu surface, indicating a higher steady-state *CO coverage at Cu|Ag interfaces. DFT explains the trends by showing that Ag-Cu motifs strengthen *CO₂/*CO and lower early barriers. Spectroscopic, theoretical, and electrochemical data together indicate a design rule for CO₂-lean flue gas that prioritizes adjacent *NOₓ-*COₓ to enable urea synthesis.