Synthesis of liquid nitrogenous fertilizer via a nitrogen conversion balance

Abstract

Nitrogen (N) fertilizer plays a crucial role in agriculture. The conventional production and use of solid nitrogenous fertilizers results in substantial energy consumption and severe groundwater pollution. Here we propose an absorption‒electroreduction relay strategy capable of the distributed production of directly accessible liquid N fertilizer (NH4NO3 solution) from NOx, a common constituent of exhaust gases. When combined with plasma-driven N fixation, the raw feedstock in this strategy can be further extended to air. NOx is first absorbed by an aqueous solution. The NOx− produced as well as the residual NOx are selectively reduced to NH4NO3 by a ruthenium‒cobalt electrocatalyst (Ru9Co91). Through the N balance established between the absorption and electroreduction processes, NH4NO3 solutions are produced continuously without any other additive ions. We successfully constructed an 8-l membrane-free system that outputs 8.5 l h−1 of NH4NO3 solution at a constant concentration (840 mg l−1 of N) to meet the N fertilizer requirements for 20 m2 of farmland. This work offers an alternative route for obtaining N fertilizers, with the potential to improve the sustainability of the N fertilizer supply. Exploring alternative nitrogen (N) fertilizer production routes is crucial to improve the sustainability of the N fertilizer supply. Here the authors develop an absorption‒electroreduction relay strategy capable of the distributed production of liquid N fertilizer from NOx or even air.