LAUSR

Acidic nitrate electroreduction reaction (NO3-RR) offers a promising route for sustainable nitrogen cycle. However, achieving high selectivity and efficiency under low-concentration acidic conditions remains challenging. Herein, we demonstrate that Cu nanosponge can adsorb low concentration nitric acid (HNO3) and efficiently convert it to ammonia (NH3). The Cu nanosponge is prepared by Cl--induced reconstruction of porous Cu nanoparticles obtained through dealloying. In a Cl--containing HNO3 solution, porous Cu nanoparticles undergo chemical oxidation to form CuCl, which reconstructs into a nanosponge through migration and electrochemical reduction, consisting of nanoparticle-supported nanosheets. The nanosponge features abundant porous structures and numerous nanoparticle-nanosheet interfaces, creating a large active surface area and providing adsorption and reaction sites for NO3-. The optimized Cu nanosponge exhibits a 92% FE for NH3 at -0.4 V vs. RHE and 90% yield of NH3 in 0.03 M HNO3, significantly outperforming Cu nanoparticle (only 66% and 47%). In situ Raman spectroscopy confirms that the nanosponge structure not only enhances NO3- adsorption but also stabilizes the key NO2- intermediate. Furthermore, we simulate industrial wastewater to convert low concentrations of nitrate into ammonium nitrate products, which are applied to plant cultivation, effectively promoting plant growth.