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 oxidized nitrogen species enables a pathway for the carbon neutral synthesis of ammonia (NH 3 ). The most oxidized form of nitrogen, nitrate (NO 3 - ) can be reduced to NH 3 via the electrocatalytic 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, we leverage the high NO 3 RR activity of Fe-based materials to synthesize a novel active particle-active support system with Fe 2 O 3 nanoparticles supported on atomically dispersed Fe-N-C. By synergizing the activity of both nanoparticles and single atom sites, the optimized 3xFe 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 (at -1.2 V versus RHE). In-situ 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, to realize the ultrahigh NO 3 RR activity. 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, a near unity FE NH3 (at -1.0 V versus RHE). 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. This article is protected by copyright. All rights reserved.