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

Electrocatalytic NO 3 − 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 Nb 2 O 5 (Nb 2 O 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 Nb 2 O 5− x . Moreover, the OV-engineered surface of Nb 2 O 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. The Nb 2 O 5− x nanorods with changeable semiconductor character and band structure could serve as an efficient catalyst for sustainable nitrate-to-ammonia electroreduction.