Mechanism of electrochemical nitrate reduction on iron Electrodes: Elucidating electron transfer pathways and ionic inhibition in membrane concentrates

The accumulation of nitrate-nitrogen in aquatic systems has led to notable adverse effects on global water environments and human health. Electrochemical methods offer a promising solution for nitrate removal, with iron cathodes demonstrating superior performance. However, a comprehensive understanding of the electrochemical reduction mechanism on iron electrodes, particularly regarding electron transfer pathways and the subsequent transformation of intermediates, is still lacking. This study delves into the electrochemical nitrate reduction mechanism on iron electrodes, revealing that the process starts with *NO 3 adsorption followed by two distinct pathways: deoxygenation (mainly producing N 2 , and mediated by *NO 2 intermediates) and hydrogenation (generating NH 4 + /NH 3 , and mediated by *NH 2 intermediates). DFT calculations demonstrate that electrochemical nitrate reduction on iron electrodes can is feasible. Notably, in the presence of Cl - , (common in real wastewater), a shift in primary reaction products from NH 3 to N 2 was observed. Additionally, the impact of inorganic ions on nitrate reduction was assessed: Mg 2+ was identified as the most significant inhibitor, reducing the reaction rate constant to 39.25 % of the control. Stability tests proved that the system can remain stable during long-term operation. These findings suggest that electrochemical reduction technologies should account for water hardness and implement appropriate pretreatment strategies to enhance efficiency. Environmental Implication. Nitrate pollution in aquatic environments poses a crucial threat to both ecosystems and human health. In this study, the mechanism of electrochemical nitrate reduction on commercial base metal electrodes was investigated, focusing on electron transfer pathways and subsequent transformation of reaction intermediates. The influence of inorganic ions on nitrate reduction efficiency was also examined in complex aqueous systems, such as membrane concentrates. The chlorine gas generated by the system can be captured in the exhaust gas treatment unit. These findings provide valuable insights for optimizing electrocatalytic treatment of nitrate contamination in practical applications.