Halogen-induced planar defects in Cu catalysts for ammonia electrosynthesis at an ampere-level current density

Abstract

The electrocatalytic nitrate reduction reaction (NO₃⁻RR) provides an effective route for removing NO₃⁻ from wastewater and converting it to valuable ammonia (NH₃). Here, we describe the halogen-incorporated Cu (Cu–X) catalysts derived from the in situ reduction of CuO nanoparticles in electrocatalytic NO₃⁻RR. Electrochemical reconstruction induces various defect active sites in Cu–X catalysts by doping different halogens. The coexisted planar twin boundary (TB) and stacking fault (SF) defects in the Cu–F electrode possess higher activity than sole SF defects in Cu–Cl and grain boundary (GB) defects in both Cu–Br and Cu–I electrodes. The electrochemical in situ spectroscopic analysis reveals that the simultaneous TB and SF defects in the Cu–F electrode enhance the adsorption capacity of reaction intermediates and improve the conversion efficiency of NO₃⁻ to NH₃. An ampere-level current density of NH₃ synthesis is achieved on the Cu–F electrode with a high yield rate of 5.22 mmol h⁻¹ cm⁻², faradaic efficiency of 96.2%, and stability over 24 h. This work provides a promising strategy to finely modulate active sites in the Cu catalyst for high-efficiency NH₃ synthesis from NO₃⁻RR.