Synergistic Regulation of ^*NO Coupling and ^*H Supply on Sulfur-Doped Zero-Valent Iron Aerogels Drives Efficient Electroreduction of Nitrate to N₂

Electrochemical nitrate (NO₃⁻) reduction to dinitrogen (N₂) is a promising approach for environmental remediation but suffers from the sluggish ^*NO coupling and excessive ^*H supply on traditional electrocatalysts. Herein, we construct a sulfur-doped zero-valent iron (Fe⁰@S) aerogel that enables highly selective electrochemical nitrate-to-dinitrogen conversion via ^*NO→^*N₂O→N₂ path by synchronously regulating ^*H supply and ^*NO coupling. Mechanistic studies reveal that the aerogel's 3D porous framework enriches local NO₃⁻ near active sites, while strategic sulfur incorporation can weaken H₂O adsorption and tune ^*NO₃⁻ binding strength, thereby lowering the energy barrier for ^*NO coupling into ^*N₂O and subsequent reduction to N₂. With a flow-through electrolyzer, we achieve near-complete removal of 50 mg/L NO₃⁻ from real surface and ground water with a high N₂ selectivity above 90%. This work provides a practical NO₃⁻ remediation method based on non-noble metals and presents a simple strategy for the design of catalyst structure to improve N₂ selectivity.