Electronic Structure Optimization and Proton-Transfer Enhancement on Titanium Oxide-Supported Copper Nanoparticles for Enhanced Nitrogen Recycling from Nitrate-Contaminated Water

Electrocatalytic reduction of nitrate to NH3 (NO3RR)on Cu offers sustainable NH3 production and nitrogen recyclingfrom nitrate-contaminated water. However, Cu affords limited NO3RRactivity owing to its unfavorable electronic state and the slow protontransfer on its surface, especially in neutral/alkaline media. Furthermore,although a synchronous "NO3RR and NH3 collection"system has been developed for nitrogen recycling from nitrate-ladenwater, no system is designed for natural water that generally containslow-concentration nitrate. Herein, we demonstrate that depositingCu nanoparticles on a TiO2 support enables the formationof electron-deficient Cu & delta;+ species (0 < & delta;& LE; 2), which are more active than Cu-0 in NO3RR. Furthermore,TiO2-Cu coupling induces local electric-field enhancementthat intensifies water adsorption/dissociation at the interface, acceleratingproton transfer for NO3RR on Cu. With the dual enhancements, TiO2-Cu delivers an NH3-N selectivity of 90.5%,mass activity of 41.4 mg-N h g(Cu) (-1), specificactivity of 377.8 mg-N h(-1) m(-2), and minimal Cu leaching (<25.4 & mu;g L-1) when treating 22.5 mg L-1 of NO3 (-)-N at -0.40 V, outperforming most of the reportedCu-based catalysts. A sequential NO3RR and NH3 collectionsystem based on TiO2-Cu was then proposed, whichcould recycle nitrogen from nitrate-contaminated water under a wideconcentration window of 22.5-112.5 mg L-1 at a rate of 209-630 mg(N) m(-2) h(-1). We also demonstrated this system could collect83.9% of nitrogen from NO3 (-)-N (19.3 mgL(-1)) in natural lake water. This work reported a robust NO3RR (electrocatalytic reductionof nitrate to NH3) catalyst and a sequential NO3RR andNH(3) collection system, which enabled efficient nitrogenrecycling from nitrates in natural water, even in a low concentration.