Structural optimization of oxygen vacancies in WO3via Cu doping for enhanced electrocatalytic nitrate reduction to ammonia

Abstract

Electrochemical nitrate reduction to ammonia not only removes harmful nitrate pollutants from wastewater but also generates valuable ammonia. In this work, Cu was introduced into WO₃, and high-concentration oxygen defects were generated using a simple hydrothermal method. Cu was then added as an electrocatalyst for nitrate reduction. In the doping process, Cu replaces the W atom in the WO₃ structure. To maintain the charge balance, WO₃ forms a higher concentration of oxygen vacancy (O_v) through the charge compensation mechanism. The abundant oxygen vacancy on the catalyst surface and the synergistic effect of Cu active sites promoted nitrate adsorption, resulting in improved NO₃RR performance. Experimental results revealed that Cu–WO₃ exhibited a high NH₃ yield of 2131.3 μg h⁻¹ mg_cat⁻¹ and a Faraday efficiency of 94% at a potential of −0.6 V (vs. RHE) in an alkaline electrolyte. ¹⁵N isotopic labeling tests confirmed the origin source of the produced ammonia. Cu–WO₃ also exhibited excellent electrochemical cycle stability and long-term durability, suggesting its application in the industrial field. In situ Fourier-transform infrared (FTIR) spectroscopy revealed that Cu–WO₃ can effectively adsorb nitrate and nitrogen dioxide intermediates. This work provides valuable insights for the exploration of efficient nitrate NO₃RR electrocatalysts.