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

The electrochemical reduction of nitrates (NO ) enables a pathway for the carbon neutral synthesis of ammonia (NH), via the nitrate reduction reaction (NORR), which has been demonstrated at high selectivity. However, to make NH synthesis cost-competitive with current technologies, high NH partial current densities (j) must be achieved to reduce the levelized cost of NH. Here, the high NORR activity of Fe-based materials is leveraged to synthesize a novel active particle-active support system with FeO nanoparticles supported on atomically dispersed Fe-N-C. The optimized 3×FeO/Fe-N-C catalyst demonstrates an ultrahigh NORR activity, reaching a maximum j of 1.95 A cm at a Faradaic efficiency (FE) for NH of 100% and an NH yield rate over 9 mmol hr cm. Operando XANES and post-mortem XPS reveal the importance of a pre-reduction activation step, reducing the surface FeO (Fe) to highly active Fe sites, which are maintained during electrolysis. Durability studies demonstrate the robustness of both the FeO particles and Fe-N sites at highly cathodic potentials, maintaining a current of -1.3 A cm over 24 hours. This work exhibits an effective and durable active particle-active support system enhancing the performance of the NORR, enabling industrially relevant current densities and near 100% selectivity.