Pulsed Design Enables Ammonia Electrosynthesis From Dilute Nitrate in Real Wastewater

Abstract

ABSTRACT Electroreduction of nitrate (NO 3 − ) to ammonia (NH 3 ) provides a sustainable method for waste valorization. However, low nitrate levels and the coexistence of interfering ions in real wastewater severely affect catalytic selectivity and stability. Herein, we report for the first time that pulsed design enables efficient NH 3 synthesis from dilute NO 3 − in real wastewater. Using diluted wastewater from a graphene production plant (∼5 mM NO 3 − with various interfering ions), the periodic application of anodic and cathodic pulses ( E a  = 0.8 V, t a  = 0.5 s, E c  = −0.4 V, and t c  = 5 s) over a Ru@Cu catalyst achieved a high NH 3 Faradaic efficiency (FE) of 90.2% and an NH 3 yield rate of 1.48 mg·h −1  cm −2 , significantly surpassing the FE(NH 3 ) of 45.0% obtained under potentiostatic conditions. Notably, the catalyst stability improved significantly under pulsed conditions, with FE(NH 3 ) remaining above 86.3% after six cycles (3 h), compared to a sharp drop to 11.4% under potentiostatic conditions. Mechanistic studies reveal that the intermittent application of a positive potential generates a localized electric field that enriches NO 3 − and repels interfering cations near the cathode, thereby mitigating hydroxide precipitation and enhancing NO 3 − availability. This work establishes a sustainable and economically viable strategy for real wastewater treatment.