Toward Green Liquid Nitrogen Fertilizer Synthesis: Plasma-Driven Nitrogen Oxidation and Partial Electrocatalytic Reduction

Liquid fertilizers, particularly when integrated with precision irrigation systems, offer a more efficient and sustainable alternative to traditional solid nitrogen fertilizers. The industrial production of ammonium nitrate (NH₄NO₃) is environmentally detrimental due to its reliance on fossil fuels. This study introduces an innovative air-to-NOx-to-NH₄NO₃ pathway for synthesizing liquid nitrogen fertilizer. The process employs an underwater multi-bubble plasma reactor powered by nanosecond pulse to generate aqueous NOx, which is then partially reduced to NH₄NO₃ through electrocatalysis. Results show that the highest NOx production rate, 786.5 mol h^-1, is achieved when the N₂/O₂ ratio closely resemble that of air, and short pulse rise/fall times significantly increase NOx yield. Further plasma diagnostic and global plasma chemistry modeling indicate that short rise/fall times facilitate simultaneous dielectric barrier discharge and spark discharge, synergistically enhancing nitrogen fixation efficiency. The partially electro-reduced liquid NH₄NO₃ fertilizer significantly improves plant growth, with stem length and leaf length increasing by 91.26% and 54.72%, respectively. Cost estimation reveals that 44.22% of the production cost is attributed to electricity consumption, underscoring the potential for optimization with renewable energy integration. Overall, the study provides new insight for the sustainable production and in-place utilization of liquid nitrogen fertilizers which may advance sustainable agriculture.