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

Abstract

It is a green and feasible approach to realize artificial nitrogen cycling through the electrocatalytic reduction of nitrate (NO 3 − ) into ammonia (NH 3 ). Nevertheless, the electrochemical nitrate-to-ammonia reduction reaction (NO 3 − RR) has been greatly hindered by low Faradaic efficiency and high applied overpotential. Herein, a few-layer reduced graphene oxide (rGO)-coated Cu 2 O nanocrystal composite (denoted as Cu 2 O@rGO) is successfully constructed by the simple hydrothermal methodology to enhance the catalytic performance of NO 3 − RR to NH 3 . Benefiting from the synergistic effects of rapid electron migration, enriched oxygen vacancies, and intimate interface, the obtained Cu 2 O@rGO catalyst accelerates the adsorption of NO 3 − and some key intermediates and inhibits the hydrogen evolution reaction (HER) during the NO 3 − RR. Consequently, the optimized Cu 2 O@rGO catalyst exhibits NH 3 Faradaic efficiency (FE) of 91.8% at −0.9 V, selectivity of up to 99%, and yield rate of 0.25 mmol, 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 NO 3 − RR to NH 3 production.