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 (Ov) 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 mgcat−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.