Ellagic Acid-M Supramolecular Assembly/Co3O4 Electrocatalysts for Efficient Nitrate Catalysis

The anthropogenic acceleration of the nitrogen cycle has exacerbated nitrate contamination in water bodies, posing threats to both ecological balance and public health. Conventional physicochemical separation and biological denitrification technologies suffer from high costs, secondary pollution, or resource wastage. The electrochemical nitrate reduction reaction (NO3RR) offers a promising route to convert nitrate into value-added ammonia, combining environmental remediation with resource recovery. However, its application is hindered by sluggish multielectron transfer kinetics and competition from the hydrogen evolution reaction (HER). The purpose of this study is to develop a high-performance NO3RR electrocatalyst with precise regulation of metal ion distribution by EA, to promote the metal-polyphenol self-assembly system from the perspective of ligand engineering, and to provide new insights for the rational design of advanced heterogeneous electrocatalysts. Building on the demonstration that the metal-polyphenol assembly strategy enhances the catalytic performance of Co3O4, we further introduced ellagic acid (EA), a small-molecule polyphenol, to coordinate and self-assemble with transition metal ions of different valence states (Fe3+, Ni2+, Cu2+). A series of EA-M/Co3O4 (M = Fe, Ni, Cu) catalysts was constructed to investigate the effects of polyphenol molecular structure and metal substitution mode on the structure and performance of Co3O4. The results show that the system exhibits excellent catalytic activity: EA-Cu/Co3O4 achieves a Faradaic efficiency of 96.83% at -0.3 V vs RHE and an NH3 yield of 279.43 μmol h-1 cm-2 at -0.5 V vs RHE. Furthermore, density functional theory (DFT) calculations elucidate the NO3RR mechanism on EA-Cu/Co3O4. Cu2+ doping modulated the electronic structure, enhanced the adsorption of reactants, and thereby promoted the NO3RR process.