Synergizing Fe 2 O 3 Nanoparticles on Single Atom Fe-N-C for Nitrate Reduction to Ammonia at Industrial Current Densities.

The electrochemical reduction of nitrates (NO ₃ ^- ) enables a pathway for the carbon neutral synthesis of ammonia (NH ₃ ), via the nitrate reduction reaction (NO ₃ RR), which has been demonstrated at high selectivity. However, to make NH ₃ synthesis cost-competitive with current technologies, high NH ₃ partial current densities (j _NH3 ) must be achieved to reduce the levelized cost of NH ₃ . Here, the high NO ₃ RR activity of Fe-based materials is leveraged to synthesize a novel active particle-active support system with Fe ₂ O ₃ nanoparticles supported on atomically dispersed Fe-N-C. The optimized 3×Fe ₂ O ₃ /Fe-N-C catalyst demonstrates an ultrahigh NO ₃ RR activity, reaching a maximum j _NH3 of 1.95 A cm ^-2 at a Faradaic efficiency (FE) for NH ₃ of 100% and an NH ₃ 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 Fe ₂ O ₃ (Fe ³⁺ ) to highly active Fe ⁰ sites, which are maintained during electrolysis. Durability studies demonstrate the robustness of both the Fe ₂ O ₃ 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 NO ₃ RR, enabling industrially relevant current densities and near 100% selectivity.
(© 2024 The Authors. Advanced Materials published by Wiley‐VCH GmbH.)