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 Co_3wt%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.