In‐tandem Electrochemical Reduction of Nitrate to Ammonia on Ultrathin‐Sheet‐Assembled Iron‐Nickel Alloy Nanoflowers

Abstract The development of alternative routes for ammonia (NH 3 ) synthesis with high Faradaic efficiency (FE) is crucial for energy conservation and to achieve zero carbon emissions. Electrocatalytic nitrate (NO 3 − ) reduction to NH 3 (e‐NO 3 RRA) is a promising alternative to the energy‐intensive, fossil‐fuel‐driven Haber–Bosch process. The implementation of this innovative NH 3 synthesis technique requires an efficient electrocatalyst and in‐depth mechanistic understanding of e‐NO 3 RRA. In this study, we developed an ultrathin sheet (μm) iron–nickel nanoflower alloy through electrodeposition and used it for e‐NO 3 RRA under alkaline conditions. The prepared Fe−Ni alloy exhibited an FE of 97.28±1.36 % at −238 mV RHE and an NH 3 yield rate up to 3999.1±242.59 μg h −1 cm −2 . Experimental electrolysis, in situ Raman spectroscopy, and density functional theory calculations showed that the adsorption and reduction of NO 3 − to NO 2 − occurred on the Fe surface, whereas subsequent hydrogenation of NO 2 − to NH 3 occurred preferentially on the Ni surface. The catalysts exhibited comparable FE for at least 10 cycles, with a long‐term stability of 216 h. Electron paramagnetic resonance results confirmed that adsorbed hydrogen was consumed during e‐NO 3 RRA. This work introduces a sustainable, robust, and efficient Fe−Ni alloy electrocatalyst, offering an environmentally friendly approach for synthesizing NH 3 from NO 3 − ‐contaminated water.