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 (NO3−) removal and producing valuable N-containing compounds. This study develops a one-step hydrothermal approach for decorating copper foam (CuF) with VO2 nanobelts. Subsequently, N2 annealing is performed to generate oxygen vacancies (OVs) and yield a VO2-x/CuF sample for its application as an electrocatalyst in reducing NO3− to ammonia (NH3). Several characterization techniques are applied to study the structural and morphological features of the VO2-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 NO3− reduction processes. The VO2-x/CuF sample demonstrates impressive results, with a NO3− conversion of 78.7 %, an NH4+ yield rate of 1.833 mmol h−1 cm−2, an NH4+ FE of 77.9 %, and a remarkable NH4+ selectivity of 99.7 % at −1.3 V vs RHE. It is worth mentioning that the isotopic labeling findings reveal that the NH4+ originated from NO3− during the electrocatalytic NO3− reduction using a VO2-x/CuF sample. This confinement method effectively creates accessible metallic catalysts with OVs, enabling high-activity, selective and stable NO3− reduction to NH4+ electrocatalysts.