Electronic Structure Optimization and Proton-Transfer Enhancement on Titanium Oxide-Supported Copper Nanoparticles for Enhanced Nitrogen Recycling from Nitrate-Contaminated Water
Zixun Liu, Fei Shen, Li Shi, Qiuwen Tong, Mue Tang, Yiming Li, Min Peng, Zhaojie Jiao, Yan Jiang, Liang Ao, Wenyang Fu, Xiaoshu Lv, Guangming Jiang, Li’an Hou
Abstract
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 nitrate-contaminated 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.