Enhancement of Selective Electrocatalytic NO3– Reduction to NH3 Over rGO-Coated Cu2O Nanoparticles

It is a green and feasible approach to realize artificial nitrogen cycling through the electrocatalytic reduction of nitrate (NO3–) into ammonia (NH3). Nevertheless, the electrochemical nitrate-to-ammonia reduction reaction (NO3–RR) has been greatly hindered by low Faradaic efficiency and high applied overpotential. Herein, a few-layer reduced graphene oxide (rGO)-coated Cu2O nanocrystal composite (denoted as Cu2O@rGO) is successfully constructed by the simple hydrothermal methodology to enhance the catalytic performance of NO3–RR to NH3. Benefiting from the synergistic effects of rapid electron migration, enriched oxygen vacancies, and intimate interface, the obtained Cu2O@rGO catalyst accelerates the adsorption of NO3– and some key intermediates and inhibits the hydrogen evolution reaction (HER) during the NO3–RR. Consequently, the optimized Cu2O@rGO catalyst exhibits NH3 Faradaic efficiency (FE) of 91.8% at −0.9 V, selectivity of up to 99%, and yield rate of 0.25 mmol·h–1·mgcat–1, much outperforming the most reported Cu-based catalysts. Moreover, the in situ infrared spectroscopy (FT-IR) displays the formation pathway of key intermediates in the catalytic process and discloses the catalytic mechanism. This work presents a simple and effective methodology to improve the activity of Cu-based electrocatalysts for the NO3–RR to NH3 production.