Coupling iron oxide with iron single-atom catalyst promotes neutral electrochemical nitrate reduction from water

Electrochemical nitrate reduction reaction (NO₃RR) presents a promising approach for sustainable water denitrification. Yet its practical implementation is hindered by sluggish reaction kinetics. Herein, we develop a dual-functional catalyst comprising carbon-wrapped Fe₃O₄ nanoparticles integrated with Fe single atom sites (FeNC-Fe₃O₄), which demonstrates exceptional activity and stability for NO₃RR. The FeNC-Fe₃O₄ achieves a Faradic efficiency of 95.63 % and an NH₃ yield of 2.95 mg cm^-2 h^-1 at -0.6 V vs. RHE in a neutral electrolyte. Mechanistic investigations, including in situ analysis and density functional theory calculations, reveal that the synergetic interplay between FeNC and Fe₃O₄ nanoparticles and the enlargement on double-layer capacitance, reduces the energy barrier for key intermediates, and provides abundant active sites for NO₃RR. Furthermore, the catalyst exhibits an 85.1 % nitrate conversion efficiency and 87.2 % N₂ selectivity at -0.6 V vs. RHE, where Cl^- play a crucial role in promoting the N₂ generation. This work underscores the potential of integrating Fe₃O₄ with FeNC to advance the practical utility of single atom catalysts, offering a design paradigm for advanced metal oxide hybrid catalysts.