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Pt nanoparticles supported on a library of 3d, 4d, 5d and f metal M–N–C catalysts for the ORR. 

Abstract The electrochemical reduction of nitrates (NO₃⁻) enables a pathway for the carbon neutral synthesis of ammonia (NH₃), via the nitrate reduction reaction (NO₃RR), which has been demonstrated at high selectivity. However, to make NH₃synthesis cost‐competitive with current technologies, high NH₃partial current densities (j_NH3) must be achieved to reduce the levelized cost of NH₃. Here, the high NO₃RR activity of Fe‐based materials is leveraged to synthesize a novel active particle‐active support system with Fe₂O₃nanoparticles supported on atomically dispersed Fe–N–C. The optimized 3×Fe₂O₃/Fe–N–C catalyst demonstrates an ultrahigh NO₃RR activity, reaching a maximum j_NH3of 1.95 A cm⁻²at a Faradaic efficiency (FE) for NH₃of 100% and an NH₃yield rate over 9 mmol hr⁻¹cm⁻². Operando XANES and post‐mortem XPS reveal the importance of a pre‐reduction activation step, reducing the surface Fe₂O₃(Fe³⁺) to highly active Fe⁰sites, which are maintained during electrolysis. Durability studies demonstrate the robustness of both the Fe₂O₃particles and Fe–N_xsites at highly cathodic potentials, maintaining a current of −1.3 A cm⁻²over 24 hours. This work exhibits an effective and durable active particle‐active support system enhancing the performance of the NO₃RR, enabling industrially relevant current densities and near 100% selectivity.