Synergizing Fe₂O₃ Nanoparticles on Single Atom Fe-N-C for Nitrate Reduction to Ammonia at Industrial Current...

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 NH₃ synthesis cost-competitive with current technologies, high NH₃ partial 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 Fe₂O₃ nanoparticles supported on atomically dispersed Fe-N-C. The optimized 3×Fe₂O₃/Fe-N-C catalyst demonstrates an ultrahigh NO₃RR activity, reaching a maximum j_NH3 of 1.95 A cm^-2 at a Faradaic efficiency (FE) for NH₃ of 100% and an NH₃ yield rate over 9 mmol hr^-1 cm^-2. Operando XANES and post-mortem XPS reveal the importance of a pre-reduction activation step, reducing the surface Fe₂O₃ (Fe³⁺) to highly active Fe⁰ sites, which are maintained during electrolysis. Durability studies demonstrate the robustness of both the Fe₂O₃ particles and Fe-N_x sites at highly cathodic potentials, maintaining a current of -1.3 A cm^-2 over 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.