Tandem Catalysis Enables High-Rate Nitrate Electroreduction via Interfacial Water Regulation.

The electrocatalytic nitrate reduction (NO₃RR) for rapid nitrate removal offers a sustainable wastewater treatment pathway, but suffers from low activity for practical applications. Herein, we synthesize a tandem catalyst with silver (Ag) nanoparticles implanted in iron phosphide (FeP) nanosheets, demonstrating a remarkable nitrate removal rate of 16.67 mg N L⁻¹ h⁻¹ (98% NO₃ ⁻-N conversion and 99% N₂ selectivity via a coupled electro-chemical pathway) and up to 40 cycles of electrocatalytic stability (6 h per cycle). Mechanistic study by a series of in situ experiments reveals a decoupling and tandem catalytic mechanism for achieving high-rate activity: the favorable nitrate reduction to nitrite on Ag nanoparticles, and the subsequent accelerated interfacial water activation with elevated local *H concentration on FeP nanosheets. Leveraging this tandem catalyst design, we further develop a paired-electrolysis flow-cell reactor integrating NO₃RR with sulfion oxidation. This system co-valorizes both contaminants by oxidizing sulfion to elemental sulfur while reducing nitrate to N₂, achieving an enhanced nitrogen removal rate of ∼ 31.7 mgN L⁻¹ h⁻¹.