Electrochemical Reduction of Nitrate to Ammonia Using Copper Oxide Catalysts

The electrochemical conversion of nitrates to ammonia offers a promising alternative to the energy- and resource-intensive Haber-Bosch process while simultaneously removing nitrates, a common water pollutant. However, this process is hindered by the eight-electron reduction required to convert nitrate to ammonia, as well as competing hydrogen evolution reactions and other nitrate reduction pathways. Efficient catalysts are essential to address these challenges, and recent studies suggest that oxide catalysts with oxygen vacancies can optimize adsorption energies of intermediates and improve catalytic performance. Copper oxides with oxygen vacancy display high ammonia selectivity in nitrate reduction, but the complexity in vacancy enrichment and the inferior hydrogen adsorption on oxides make nitrate reduction an inefficient process. In this study, a CuO x composite electrode was synthesized using the hydrothermal method, and its performance was evaluated for efficient conversion of nitrate to ammonia. The synthesized CuO x nanostructure was characterized using X-ray diffraction to determine phase purity and crystal structure, while surface morphology of prepared samples was examined with high resolution transmission electron microscope. The results of X-ray photoelectron spectroscopy suggested that there were abundant oxygen vacancies on the surface of the CuOx, which can act as nitrate adsorption sites. The obtained CuO x composite electrode performs at a high ammonia Faradaic efficiency of over 80% and long-term stability due to interfacial coupling effects. These findings highlight the potential of CuO x catalysts for electrochemical nitrate reduction, offering new opportunities for sustainable nitrogen management and water treatment.