Electrocatalytic reduction of nitrate to NH 3 (NO3RR) on Cu offers sustainable NH 3 production and nitrogen recycling from nitrate-contaminated water. However, Cu affords limited NO3RR activity owing to its unfavorable electronic state and the slow proton transfer on its surface, especially in neutral/alkaline media. Furthermore, although a synchronous "NO3RR and NH 3 collection" system has been developed for nitrogen recycling from nitrate-laden water, no system is designed for natural water that generally contains low-concentration nitrate. Herein, we demonstrate that depositing Cu nanoparticles on a TiO 2 support enables the formation of electron-deficient Cu δ+ species (0 < δ ≤ 2), which are more active than Cu 0 in NO3RR. Furthermore, TiO 2 −Cu coupling induces local electric-field enhancement that intensifies water adsorption/ dissociation at the interface, accelerating proton transfer for NO3RR on Cu. With the dual enhancements, TiO 2 −Cu delivers an NH 3 -N selectivity of 90.5%, mass activity of 41.4 mg-N h g Cu −1 , specific activity of 377.8 mg-N h −1 m −2 , and minimal Cu leaching (<25.4 μg L −1 ) when treating 22.5 mg L −1 of NO 3 − -N at −0.40 V, outperforming most of the reported Cu-based catalysts. A sequential NO3RR and NH 3 collection system based on TiO 2 −Cu was then proposed, which could recycle nitrogen from nitratecontaminated water under a wide concentration 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 collect 83.9% of nitrogen from NO 3 − -N (19.3 mg L −1 ) in natural lake water.

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