Highly selective and stable electrochemical reduction of nitrate to ammonia using VO2-x /CuF catalyst with oxygen vacancies

Electrocatalytic reduction poses significant challenges due to slow kinetics, limited selectivity, and instability, hindering its potential for sustainable nitrate (NO 3 - ) removal and producing valuable N -containing compounds. This study develops a one-step hydrothermal approach for decorating copper foam (CuF) with VO 2 nanobelts. Subsequently, N 2 annealing is performed to generate oxygen vacancies (OVs) and yield a VO 2-x /CuF sample for its application as an electrocatalyst in reducing NO 3 - to ammonia (NH 3 ). Several characterization techniques are applied to study the structural and morphological features of the VO 2-x /CuF sample, which shows a high crystalline and defective bundle-like structure of nanobelts attributed to the release of oxygen atoms that are beneficial for the electrochemical NO 3 - reduction processes. The VO 2-x /CuF sample demonstrates impressive results, with a NO 3 - conversion of 78.7 %, an NH 4 + yield rate of 1.833 mmol h -1 cm - 2 , an NH 4 + FE of 77.9 %, and a remarkable NH 4 + selectivity of 99.7 % at -1.3 V vs RHE. It is worth mentioning that the isotopic labeling findings reveal that the NH 4 + originated from NO 3 - during the electrocatalytic NO 3 - reduction using a VO 2-x /CuF sample. This confinement method effectively creates accessible metallic catalysts with OVs, enabling highactivity, selective and stable NO 3 - reduction to NH 4 + electrocatalysts.