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

ABSTRACT Ammonium nitrate (NH 4 NO 3 ) 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 NH 4 NO 3 from air and water by integrating plasma‐assisted nitrogen oxidation (pNOR) with paired electrocatalytic nitrite reduction and oxidation (eNO 2 – RR/eNO 2 – 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 eNO 2 – RR step, which operates via a dual‐active‐site mechanism: Cu sites adsorb and activate NO 2 – , while adjacent Co sites efficiently dissociate water to generate reactive hydrogen species (*H). Subsequent hydrogen spillover from Co to Cu sites dramatically accelerates NO 2 – hydrogenation to NH 4 + , achieving almost 100% Faradaic efficiency toward NH 3 and a high NH 4 + yield rate of 512 µmol cm −2 h −1 at a low potential of –0.5 V vs. RHE. The integrated pNOR‐eNO 2 – RR/eNO 2 – OR system operates stably over 210 h (affording 8.5 mmol h −1 NH 4 NO 3 ) with significant techno‐economic advantages. Further, the obtained NH 4 NO 3 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.