Sulfur-dopant-promoted electrocatalytic reduction of nitrate by a self-supported iron cathode: Selectivity, stability, and underlying mechanism

The electrocatalytic reduction of nitrate (NO 3 − ) to ammonia (NH 4 + ) and further oxidation to N 2 via active chlorine is an effective method for denitrification. High activity, NH 4 + –N selectivity and long-term stability of a cathode are essential for the application. Herein, we reported a sulfur-modified Fe foam (FeS x @FF) cathode, which achieved high NO 3 − –N conversion (94.96%) and NH 4 + –N selectivity (82.29%) due to its enhanced electron transfer, atomic hydrogen (H*) generation, and adsorption of NO 3 − . Combined in-situ differential electrochemical mass spectrometry and theoretical calculations reveal that the ultrafast *NO 3 reduction to *NO 2 and low formation energy of *NO are crucial in reduction of *NO 3 to *NH 3 . The FeS 0.2 @FF cathode for realistic industrial wastewater (∼350 mg L −1 NO 3 − –N) treatment shows high TN removal (90.75%) and N 2 selectivity (98.88%) with an ultralow electrical cost (∼0.22 kWh g −1 N). This designed system has potential for efficient NO 3 − removal in the saline wastewater.