Mild Oxidant Regulation of *H Coverage Promotes Electrocatalytic Nitrate Reduction to N2 in Low-Conductivity Media

Abstract

Electrocatalytic nitrate reduction reaction (NO3RR) has attracted growing interest for converting nitrate (NO3–) into ammonium (NH4+), yet NH4+ production from dilute, low-conductivity waters is constrained by high energy consumption, limited NO3– availability, and costly product recovery. Steering NO3RR directly toward benign N2 therefore represents a more practical route, but this pathway is often suppressed by excessive surface *H coverage, which drives the overhydrogenation of nitrogen intermediates to NH4+. Here, we report a mild oxidant-assisted coelectrolysis strategy that regulates interfacial *H coverage and promotes NO3–-to-N2 conversion in a Cu nanoparticle-decorated Ni cathode membrane electrochemical reactor. This reactor separates a highly conductive electrochemical chamber from a NO3–-containing chemical chamber, enabling NO3– reduction in low-conductivity media while maintaining a less negative cathodic potential. Mild oxidants, including H2O2, O2, CH3COOOH, and KIO4, consumed excess *H and redirected the reaction pathway toward N–N coupling. With H2O2 as a representative oxidant, N2 selectivity increased from 13.47% without H2O2 to 87.25% at 100 mM H2O2. Mechanistic analyses revealed that H2O2 decreases interfacial *H abundance, which suppresses NH4+ formation and facilitates the dimerization of nitrogen-containing intermediates. Verification in real low-conductivity groundwater further supports this strategy as a mechanistic basis for designing selective, low-energy electrochemical denitrification systems for low-conductivity NO3–-contaminated media.