Highly selective and stable electrochemical reduction of nitrate to ammonia using VO_2-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 VO_2-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 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 NO₃⁻ reduction processes. The VO_2-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 VO_2-x/CuF sample. This confinement method effectively creates accessible metallic catalysts with OVs, enabling high-activity, selective and stable NO₃⁻ reduction to NH₄⁺ electrocatalysts.