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

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.