Enhancement of Selective\nElectrocatalytic NO<sub>3</sub><sup>–</sup> Reduction to NH<sub>3</sub> Over rGO-Coated Cu<sub>2</sub>O Nanoparticles

It is a green and feasible approach to realize artificial\nnitrogen\ncycling through the electrocatalytic reduction of nitrate (NO<sub>3</sub><sup>–</sup>) into ammonia (NH<sub>3</sub>). Nevertheless,\nthe electrochemical nitrate-to-ammonia reduction reaction (NO<sub>3</sub><sup>–</sup>RR) has been greatly hindered by low Faradaic\nefficiency and high applied overpotential. Herein, a few-layer reduced\ngraphene oxide (rGO)-coated Cu<sub>2</sub>O nanocrystal composite\n(denoted as Cu<sub>2</sub>O@rGO) is successfully constructed by the\nsimple hydrothermal methodology to enhance the catalytic performance\nof NO<sub>3</sub><sup>–</sup>RR to NH<sub>3</sub>. Benefiting\nfrom the synergistic effects of rapid electron migration, enriched\noxygen vacancies, and intimate interface, the obtained Cu<sub>2</sub>O@rGO catalyst accelerates the adsorption of NO<sub>3</sub><sup>–</sup> and some key intermediates and inhibits the hydrogen evolution reaction\n(HER) during the NO<sub>3</sub><sup>–</sup>RR. Consequently,\nthe optimized Cu<sub>2</sub>O@rGO catalyst exhibits NH<sub>3</sub> Faradaic efficiency (FE) of 91.8% at −0.9 V, selectivity\nof up to 99%, and yield rate of 0.25 mmol·h<sup>–1</sup>·mg<sub>cat</sub><sup>–1</sup>, much outperforming the\nmost reported Cu-based catalysts. Moreover, the <i>in situ</i> infrared spectroscopy (FT-IR) displays the formation pathway of\nkey intermediates in the catalytic process and discloses the catalytic\nmechanism. This work presents a simple and effective methodology to\nimprove the activity of Cu-based electrocatalysts for the NO<sub>3</sub><sup>–</sup>RR to NH<sub>3</sub> production.