Integrated Three-in-one to Boost Nitrate Electroreduction to Ammonia Utilizing a 1D Mesoporous Carbon Cascade Nanoreactor.

Abstract

The electrochemical reduction of nitrate (NO₃^-) offers a promising waste-to-value strategy for synthesizing ammonia (NH₃), yet it involves a complex multi-interface system with several stages such as mass transport, species enrichment, and interfacial transformation. This complexity necessitates catalysts with diverse structural characteristics across multiple temporal and spatial scales. Herein, a three-in-one nanoreactor system is designed with 1D geometry, open mesochannels, and synergistic active sites for optimized NH₃ synthesis. Guided by finite element simulations, a 1D mesoporous carbon carrier is engineered to create a distinctive microenvironment that enhances NO₃^- transfer and adsorption while confining reaction intermediates. Meanwhile, iron single atomic sites (Fe-N₄ SAs) and iron nanoclusters (Fe₄ NCs) are embedded in situ into the carbon carrier, yielding an efficient cascade nanoreactor. This design demonstrates large Faraday efficiencies, rapid NO₃^- removal rates, and impressive NH₃ yield rates under both neutral and alkaline conditions. Detailed in situ experimental results and theoretical analysis reveal that Fe-N₄ SAs and Fe₄ NCs can adapt their electronic structures in tandem, allowing the Fe-N₄ SAs to effectively reduce NO₃^- and Fe₄ NCs to oxidize H₂O. As a demonstration, the assembled Zn-NO₃^- battery achieves a power density of 20.12 mW cm^-2 coupled with excellent rechargeability.