Significance: Electrochemical reduction of nitrate pollution in water into value-added ammonium is essential for modern agriculture and industry and represents a potentially sustainable strategy to replace the traditional Haber–Bosch process. However, the nitrate reduction reaction (NO ₃ ⁻ RR) process under ambient conditions often suffers from low selectivity. Here, we developed a strategy of tuning an electronic structure for preparing cobalt-doped Fe@Fe ₂ O ₃ electrocatalysts. Cobalt doping tunes the Fe d-band center, thereby modulating the adsorption energies of intermediates and suppressing hydrogen production. Therefore, the electrocatalysts exhibit superior NO ₃ ⁻ RR activity with a high nitrate removal capacity (100.8 mg N g _cat ⁻¹ h ⁻¹ ), NH ₃ selectivity (99.0 ± 0.1%), and faradaic efficiency (85.2 ± 0.6%). This strategy provides an approach to design advanced materials for NO ₃ ⁻ RR.

Efficient n = O bond activation is crucial for the catalytic reduction of nitrogen compounds, which is highly affected by the construction of active centers. In this study, n = O bond activation was achieved by a single-atom catalyst (SAC) with phosphorus anchored on a Co active center to form intermediate N -species for further hydrogenation and reduction. Unique phosphorus-doped discontinuous active sites exhibit better n = O activation performance than conventional N -cooperated single-atom sites, with a high Faradic efficiency of 92.0% and a maximum ammonia yield rate of 433.3 μg NH4·h ⁻¹ ·cm ⁻² . This approach of constructing environmental sites through heteroatom modification significantly improves atom efficiency and will guide the design of future functional SACs with wide-ranging applications.