A Review on Preparation, Characterization, and Performance of Cu-Based Electrodes for Nitrogen/Nitrate Reduction Reaction

Abstract

The removal of nitrogen species, particularly nitrates, is critically important for environmental remediation and the production of renewable energy. Converting nitrogen in wastewater into ammonia is an alternative to the Haber-Bosch process, which constitutes an effective and economical method for addressing nitrate contamination in source waters. This process simultaneously facilitates the reclamation of nitrogen as a renewable and promising energy resource. This approach not only decreases dependence on energy-consuming procedures but is also environmentally friendly. Copper-based electrocatalysts for the nitrogen/nitrate reduction reaction (NRR) have been widely studied, yet a comprehensive understanding of the relationships between their preparation, characterization, and catalytic activity remains incomplete. In this review, we aim to provide a structured summary of synthetic approaches for Cu-based electrodes using both physical and chemical methods, highlighting the structure–activity correlations between synthesis strategies and catalyst performance. We also present a thorough overview of advanced characterization techniques, including structural, morphological, compositional, electrochemical, and in situ/operando studies, to identify active sites, reaction intermediates, and degradation pathways. The electrocatalytic performance of Cu-based electrodes in NRR is critically analyzed and compared, with emphasis on the effects of morphology, surface composition, electrolyte selection, and pH on activity and selectivity. Methods for quantifying ammonia, such as colorimetry, NMR, GC, and ion chromatography, are reviewed to ensure benchmarking and reproducibility. Despite these advances, practical application remains limited due to challenges such as the trade-off between selectivity and activity, catalytic deactivation, and competition from the hydrogen evolution reaction (HER). This work aims to provide a consistent and rational framework for screening Cu-based systems toward highly efficient and cost-effective ammonia electrosynthesis.

Graphical Abstract