Robust Electrocatalytic Nitrate-to-N2 Conversion Enabled by Engineered Bi2O3-Cu2O Heterojunction on Cu foam under High-Salinity and Wide-pH Conditions

Abstract

Nitrate pollution comes from farm fertilizers, industrial wastewater, and domestic sewage, causing serious harm to ecosystems and drinking water. Electrochemical nitrate reduction can use renewable energy to change nitrate (NO3-) into harmless N2, however, is often hindered by low N2 selectivity and sensitivity to complex pollution, especially high-salinity industrial wastewater with varying pH. Herein, we developed a Bi2O3-Cu2O heterojunction on Cu foam (Bi-Cu@CF) to solve nitrate pollution in high-salt industrial wastewater under a wide pH range. This electrode can remove 97% of nitrate and reach 94% of N2 selectivity in a chloride-containing system under -1.3 V (vs saturated calomel electrode) with good stability of 108 h. This system also shows strong resistance to common coexisting anions (C2O4 -, PO4 2-, and S2O8 2-) in high-salt environments and across a wide pH range. Mechanism studies show that the Bi2O3-Cu2O heterojunction interface promotes water break down to form hydrogen radicals (•H) due to its local alkalinity. These •H radicals accelerate the hydrogenation and deoxidation of nitrates to produce NH3. Meanwhile, active chlorine species (HClO) formed by the oxidation of native Cl- can oxidize the by-product NH3 into N2. Bi-Cu@CF system forms a reduction-oxidation process for efficient nitrate removal in high-salt wastewater. This study provides a stable and practical method to treat nitrate pollution in industrial wastewater.