Electrochemically converting nitrate (NO₃ ^-) into ammonia (NH₃) has emerged as an alternative strategy for NH₃ production and effluent treatment. Nevertheless, the electroreduction of dilute NO₃ ^- is still challenging due to the competitive adsorption between various aqueous species and NO₃ ^-, and unfavorable water dissociation providing ^*H. Herein, a new tandem strategy is proposed to boost the electrochemical nitrate reduction reaction (NO₃RR) performance of Cu nanoparticles supported on single Fe atoms dispersed N-doped carbon (Cu@Fe₁-NC) at dilute NO₃ ^- concentrations (≤100 ppm NO₃ ^--N). The optimized Cu@Fe₁-NC presents a FE_NH3 of 97.7% at -0.4 V versus RHE, and a significant NH₃ yield of 1953.9 mmol h^-1 g_Cu ^-1 at 100 ppm NO₃ ^--N, a record-high activity for dilute NO₃RR. The metal/carbon heterojunctions in Cu@Fe₁-NC enable a spontaneous electron transfer from Cu to carbon substrate, resulting in electron-deficient Cu. As a result, the electron-deficient Cu facilitates the adsorption of NO₃ ^- compared with the pristine Cu. The adjacent atomic Fe sites efficiently promote water dissociation, providing abundant ^*H for the hydrogenation of ^*NO_x e at Cu sites. The synergistic effects between Cu and single Fe atom sites simultaneously decrease the energy barrier for NO₃ ^- adsorption and hydrogenation, thereby enhancing the overall activity of NO₃ ^- reduction.

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