Electrochemical nitrate-to-ammonia conversion over a broad concentration range via a hollow Co3O4/CuO catalyst

Abstract

Widespread nitrate contamination in water challenges both aquatic ecosystems and drinking water safety, and the electrocatalytic nitrate reduction to ammonia (eNRA) presents a promising sustainable way to convert pollutants to value-added products. However, most existing eNRA systems operate efficiently only under highly alkaline and concentrated conditions that are incompatible with real wastewater. Herein, we report a hollow heterostructured Co₃O₄/CuO catalyst that permits efficient eNRA in neutral aqueous media over a wide range of environmentally relevant nitrate concentrations (1–250 mM). The catalyst achieves NH₃ faradaic efficiencies above 97% in the 10–250 mM nitrate range and maintains a faradaic efficiency of 86% even at 1 mM nitrate. Furthermore, the catalyst exhibited excellent stability over 100 hours of continuous operation. In situ Fourier transform infrared spectroscopy analysis suggests that the hollow architecture creates a spatially confined microenvironment that accelerates the hydrogenation of NO_x intermediates toward NH₃, and density functional theory calculations indicate the ensemble effect of Co₃O₄ and CuO in reducing the free-energy changes of key nitrate reduction steps. This work highlights a structural engineering strategy in electrocatalysts for efficient nitrate remediation and wastewater treatment.