# Synergetic Relay Between Atomic Hydrogen and Chlorine Radicals Enables Efficient Nitrate‐to‐Nitrogen Gas Conversion

## TL;DR

A new method converts harmful nitrate in water to harmless nitrogen gas using a relay of hydrogen and chlorine radicals, achieving high efficiency and minimal byproducts.

## Contribution

This is the first report of a synergistic reduction-oxidation process using H* and Cl• for nitrate-to-N2 conversion with near-complete selectivity.

## Key findings

- The system achieved 97.4% nitrate removal and nearly 100% nitrogen gas selectivity.
- Ammonium accumulation was significantly suppressed through spatial decoupling of reactions.
- The radical-relay mechanism enables efficient tandem reactions for deep denitrification.

## Abstract

The excessive discharge of nitrate (NO3
−) contamination in wastewater can lead to eutrophication of aquatic ecosystems, calling for technologies that can selectively reduce it to non‐toxic and harmless nitrogen gas (N2) reducing the secondary pollution risks. This work, for the first time, reports a synergic reduction−oxidation process that achieves highly efficient conversion of NO3
− to N2 via a relay strategy using reactive atomic hydrogen (H*) and chlorine radicals (Cl•). The photoelectrocatalytic system comprising a CuO‐Fe3O4/nickel foam (CuO‐Fe3O4/NF) and TiO2 nanotube arrays as the cathode and photocathodes, respectively, achieving a NO3
− removal rate of 97.4% and N2 selectivity close to 100%, while significantly suppressing the key bridging intermediate NH4
+ accumulation and outperforming most reported values up to date. Mechanistic studies reveal that the cathodic CuO‐Fe3O4 component achieves the strong adsorption ability at CuO sites and hydrogenation reaction at Fe3O4 sites for activating H2O to generate reductive atomic H*, then highly selectively generate the NH4
+ by spatial decoupling adsorption‐transformation processes. Subsequently, in‐situ generated Cl• by the photoanode TiO2, effectively scavenges and oxidizes NH4
+, ultimately converting it to N2 via the tandem radical‐mediated reactions. Our discovery provides a sustainable strategy and drive great advances for removing nitrate pollutants in real aquatic environments.

Using photoelectrochemical (PEC) deep denitrification technology, a novel synergistic reduction‐oxidation process enables efficient conversion of nitrate (NO3
−) to nitrogen (N2), while suppressing key intermediate ammonium (NH4
+) and toxic nitrite (NO2
−) accumulation. This reductive H*‐oxidative Cl• coupling forms an efficient “radical‐relay” chain, achieving 97.4% NO3
− removal and near‐100% N2 selectivity.