Selective conversion of nitrate to nitrogen gas by enhanced electrochemical process assisted by reductive Fe(II)-Fe(III) hydroxides at cathode surface

• Inorganic nitrogen was exhaustively converted to N 2 by the electrochemical system. • In situ electrogenerated iron hydroxides was identified at cathode surface. • NO 3 − was reduced due to direct e − , indirect H* and iron hydroxides reduction. • Electrochemical chlorination was mainly responsible for NH 4 + oxidation. • A stable TN removal above 94.1 % for real wastewater treatment was achieved. A selective electrocatalytic system for the exhaustive conversion of inorganic nitrogen to nitrogen gas (N 2 ) is developed, whereby the total nitrogen (TN) removal and N 2 selectivity achieve 96.8 % and 99.6 % in 120 min, respectively. Cyclic voltammetry reveals the feasibility of electrooxidative chlorination of NH 4 + compared to direct anodic oxidation. The TN removal is ranging from 96.2% to 99.7% under various inorganic nitrogen ratios. Green rust (GR) of mixed Fe(II)-Fe(III) hydroxides is identified at cathode surface by in-situ Raman analysis, donating electrons to NO 3 − . Direct electron reduction, indirect atomic H* reduction, and GR induced reduction are integrated for the rapid NO 3 − conversion at cathode interface. Treatment of authentic wastewater of nickel plating in continuous running further demonstrates the superiority and durability of the electrochemical system for both NO 3 − and TN abatement. The electrochemical system has potential for efficient and stable nitrogen pollutants removal in the high-salinity wastewater.