A hybrid plasma-electro-membrane triple intensified system over PdNPs/Fe–N–C for ammonium fertilizer synthesis

Upgrading nitrogen into ammonium fertilizer under environmental conditions presents a promising prospect for the application of distributed renewable energy. Herein, a hybrid plasma-electro-membrane triple intensified system is developed for the synthesis of ammonium fertilizers. Initially, the air undergoes transformation into NO₂⁻ through the use of plasma. Then, Pd_NPs/Fe–N–C, which is composed of palladium nanoparticles (Pd_NPs) and iron single atoms (Fe–N–C), was employed as the catalyst for the NO₂⁻ electroreduction reaction (NO₂⁻RR), exhibiting a remarkable NH₃ yield rate of 92.7 mg h⁻¹ mg_cat⁻¹, corresponding to a faradaic efficiency (FE) of nearly 100%. Experimental and theoretical analyses showed that Fe–N–C is the active site for NO₂⁻ reduction, and Pd_NPs can dissociate water to produce adsorbed hydrogen for nitrogen intermediate reduction. The electron transfer between Pd_NPs and the Fe–N–C makes the spin configuration of Fe change from a low to a medium spin state, thereby decreasing the energy barrier of the *NO hydrogenation process during the NO₂⁻RR. Finally, the NH₃-containing electrolyte is passed through a membrane separation reactor optimized for mass transfer to achieve NH₃ recovery and ammonium fertilizer synthesis. The Pd_NPs/Fe–N–C driven hybrid system achieves a high (NH₄)₂SO₄ yield of 685.8 mg h⁻¹, which can also be applied to the synthesis of other ammonium fertilizers.