Electrocatalytic Fixation of Nitrate Pollutants for Green Fuel Production and Metal-Nitrate Battery Application

Ammonia is a promising green fuel, fertilizer, hydrogen carrier, and an industrially demanding chemical. Simultaneous mitigation of nitrate (NO3–) pollution and green ammonia (NH3) production at normal conditions is a promising pathway achievable via electrochemical approaches. However, this strategy faces practical challenges, including sluggish multielectron transfer kinetics, low nitrate adsorption rates, and deprived reaction selectivity because of the parasitic hydrogen evolution reaction (HER). An efficient Fe3C-encapsulated N-doped CNT (FCNC) heterostructure is synthesized for the catalysis of nitrate reduction reaction (NO3RR). FCNC exhibits 93 mV dec–1 Tafel slope, 71% Coulombic efficiency for NH3, and 412 μmol h–1 cm–2 product yield at −0.65 V vs RHE. A direct correlation between the Fe2+/Fe3+ ionic ratio in the heterostructure and the NO3RR efficiency is established. Hydrophobicity studies using contact angle measurements reveal that moderately water-repellent FCNC surfaces exhibit enhanced Faradaic efficiency and selectivity toward the NO3RR, effectively suppressing HER. Mott–Schottky analysis further indicates that a lower flat band potential and higher donor density contribute to an accelerated reaction rate. Finally, we demonstrate a practical NO3RR-based energy device showing promising performance with an OCP of 0.65 V with a 3.8 mW cm–2 maximum power on 20 mA cm–2. DFT analysis also signifies that the encapsulated FCNC system has reduced adsorption of water molecules on its catalytic surface in comparison to the nonencapsulated system, thus favoring better NO3RR selectivity. Thus, through this work, a feasible route for pollutant-to-energy conversion through sustainable electrochemical nitrate reduction has been achieved.