Cu Nanoclusters and Rh Single-Atom-Modified N-Doped Carbon for Electroreduction of Nitrate to Ammonia

To tackle the pressing issue of nitrate (NO₃^-) pollution in wastewater and simultaneously convert it into ammonia (NH₃), Cu nanocluster-modified Rhodium (Rh) single atoms anchored on N-doped carbon were synthesized via pyrolysis of a zeolitic imidazolate framework-8 (ZIF-8) precursor and applied to the electrochemical reduction of nitrate at a low concentration. Structural characterizations (X-ray powder diffractometer (XRD), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), and X-ray photoelectron spectroscopy (XPS)) confirmed the coexistence of Rh single atoms and Cu nanoclusters as well as their strong electronic interactions. Mechanistic investigations revealed that Rh sites enhanced *H generation via water dissociation and promoted NO₃^- adsorption, thereby facilitating *H transfer and subsequent hydrogenation steps. As a result, the optimized Cu_97.5Rh_2.5/NC catalyst exhibited outstanding NO₃^-RR performance, with a Faradaic efficiency (FE) of 84.53%, an NH₃ yield rate of 1252.22 μg·h^-1 mg_cat^-1 at -1.0 V vs reversible hydrogen electrode (RHE), an NH₃ selectivity of 89.13% at -1.0 V vs RHE, and a NO₃^- conversion rate of 93.34% at -1.1 V vs RHE. This work presents a rational design for atom-economical catalysts, enabling sustainable NH₃ electrosynthesis from nitrate-laden wastewater and reducing effluent NO₃^--N to meet World Health Organization (WHO) drinking water standards.