Sustainable Synthesis of Ammonium Nitrate From Air and Water via Tandem Plasma-Electrolyzer System.

Ammonium nitrate (NH4NO3) is an indispensable high-nitrogen fertilizer, yet its conventional industrial production via the energy-intensive Haber-Bosch and Ostwald processes accounts for a significant global carbon footprint. Herein, we report an alternative method for directly synthesizing NH4NO3 from air and water by integrating plasma-assisted nitrogen oxidation (pNOR) with paired electrocatalytic nitrite reduction and oxidation (eNO2 -RR/eNO2 -OR) in a neutral medium (0.5 M phosphate buffer solution). Key to this technology is the rational design of a Co3wt%Cu@C cathode catalyst for the critical eNO2 -RR step, which operates via a dual-active-site mechanism: Cu sites adsorb and activate NO2 -, while adjacent Co sites efficiently dissociate water to generate reactive hydrogen species (*H). Subsequent hydrogen spillover from Co to Cu sites dramatically accelerates NO2 - hydrogenation to NH4 +, achieving almost 100% Faradaic efficiency toward NH3 and a high NH4 + yield rate of 512 µmol cm-2 h-1 at a low potential of -0.5 V vs. RHE. The integrated pNOR-eNO2 -RR/eNO2 -OR system operates stably over 210 h (affording 8.5 mmol h-1 NH4NO3) with significant techno-economic advantages. Further, the obtained NH4NO3 solutions can serve as N-P-K fertilizer for plant growth, offering a route to on-demand, on-site fertilizer synthesis from air and water for smart agriculture.