Synergistic CuCo tandem catalysis and F doping induced hydrogen bonding enable highly efficient nitrate reduction to ammonia

Abstract

The electrochemical nitrate reduction reaction (eNO₃RR) provides a sustainable pathway for ammonia synthesis while addressing nitrate pollution. However, complex intermediates and strong *H dependence in alkaline media hinder efficient NH₃ generation. Herein, an F-doped carbon-coated bimetallic Cu/Co tandem catalyst (Cu/Co@FC) is first reported, exhibiting as high as Faradaic efficiency of 96.6 % and ammonia yield of 17,779.2 μg h^-1 mg_cat^-1 in 0.1 M KOH and 0.1 M NO₃^- at -0.95 V (vs. RHE). Remarkably, Cu/Co@FC showcases excellent stability by maintaining stable even after 60 h of continuous electrolysis in a flow cell at a relatively high current density of 450 mA cm^-2. In-situ characterization and theoretical calculations reveal that Cu serves as the site for NO₃^- adsorption and activation, while Co facilitates the reduction of *NO₂. This synergy ensures the continuity of subsequent reactions and prevents nitrite accumulation in the electrolyte. Notably, F doping in the catalyst facilitates the formation of O-H⋯F hydrogen bonds with adsorbed H₂O. This weakens the H-OH bond and accelerates water dissociation, thereby supplying abundant *H for the hydrogenation process in eNO₃RR. Thus, the efficient tandem of Cu and Co sites, and the F doping-induced O-H⋯F hydrogen bond interactions in Cu/Co@FC effectively boost the eNO₃RR performance.

Keywords: Bimetallic sites; Electrochemical nitrate reduction; F doping; Hydrogen bond interaction; Tandem catalysis.