Enhancing selective nitrate reduction to ammonia by oxygen vacancies in cerium-modified copper and iron oxides derived from metal organic frameworks

The electrochemical conversion of nitrate (NO₃^-) to ammonia (NH₃) is both environmentally and economically desirable. However, this process is often challenged by low selectivity, limited Faradaic efficiency, and catalyst instability. In this study, we propose a novel strategy to enhance catalytic performance by incorporating cerium into copper and iron oxides derived from metal-organic frameworks (MOFs), thereby engineering abundant oxygen vacancies. Characterization via X-ray photoelectron spectroscopy (XPS) and Raman spectral analysis confirms the formation of mixed-valence metal oxides and the presence of oxygen defects associated with activated oxygen species. Electrochemical evaluations reveal that CeCuO_x and CeFeO_x exhibit NH₃ yield rates of 2428.11 and 2928.23μg h^-1 cm^-2, respectively, with peak Faradaic efficiencies of 70.0 % and 81.9 % at -0.4 V vs. RHE in 1 M KOH containing 0.1 M KNO₃. The maximum selectivity for NH₃ production exceeds 97 %, underscoring the role of cerium incorporation in promoting active site generation, defect engineering, enhanced conductivity, and proton adsorption. This work provides a promising approach for the rational design of advanced heterogeneous catalysts for electrochemical nitrate reduction and related environmental applications.