Tandem Catalysis Sites in Co‐NO/C for Efficient and Scalable Electrocatalytic Nitrate to Ammonia Conversion

ABSTRACT Electrocatalytic nitrate reduction to ammonia (eNO 3 RA) represents an emerging strategy for coupling nitrate remediation with nitrogen recovery and value‐added ammonia production, but it remains challenging to simultaneously promote nitrate activation and downstream hydrogenation. Herein, we report a Co ‐NO/C catalyst featuring Co 3 O 4 /Co 4 N tandem catalysis sites embedded in a conductive carbon matrix. Structural and spectroscopic analyses suggest that Co 3 O 4 sites mainly favor nitrate adsorption/activation, whereas Co 4 N sites facilitate interfacial active‐hydrogen generation. In an H‐type cell, Co‐NO/C delivers high NH 3 selectivity over a broad potential window and reaches a Faradaic efficiency of 99.7% at −0.6 V vs. RHE, with an NH 3 yield rate of 62.4 mg h −1 mg cat. −1 . Online differential electrochemical mass spectrometry (DEMS), 15 N isotopic labeling, in situ attenuated total reflection Fourier‐transform infrared spectroscopy (ATR‐FTIR), in situ electrochemical impedance spectroscopy (EIS), and spatially resolved scanning vibrating probe (SVP) measurements collectively support a stepwise nitrate‐to‐ammonia pathway involving sequential adsorption, deoxygenation, and hydrogenation of NO x ‐derived intermediates. Density functional theory (DFT) calculations and molecular dynamics (MD) simulations further indicate spontaneous nitrate adsorption on Co 3 O 4 and favorable H * formation on Co 4 N sites. Device demonstrations in Zn–NO 3 − batteries and a membrane electrode assembly (MEA) reactor further suggest the practical promise of this tandem‐site design for eNO 3 RA.