Oxygen-vacancy-containing Nb2O5 nanorods with modified semiconductor character for boosting selective nitrate-to-ammonia electroreduction

Abstract

Electrocatalytic NO₃⁻ reduction to ammonia (ENRA) is a sustainable approach that allows the direct synthesis of ammonia at room temperature, while solving the problem of nitrate polluted effluents. Herein, we demonstrate that the oxygen vacancies (OVs) in Nb₂O₅ (Nb₂O_5−x) nanorods exhibit significantly enhanced ENRA activity, with an ammonia faradaic efficiency of 85.1% and selectivity of 90.8% at −1.1 V versus the reversible hydrogen electrode (RHE). Introducing OVs not only improves the surface activity but also facilitates the charge transport of Nb₂O_5−x. Moreover, the OV-engineered surface of Nb₂O_5−x alters the semiconducting behaviour of the catalyst by suppressing the hydrogen evolution reaction (HER) to improve the selective production of ammonia. We believe that this research will pave the way for the development of defect-engineered metal oxide catalysts for the selective ENRA process.