Carbon-Bonded Fe₃C-Based Electrocatalysts Derived from Metal-Coordination Polymers for Efficient Nitrate Reduction to...

Electrochemical reduction of nitrate (NO₃ ^-) offers a sustainable route for synthesizing ammonia (NH₃) and thus balancing the nitrogen cycle. Metallic Fe has been dominantly explored as a low-cost and efficient catalysts for this process, which, however, suffers from intrinsically poor stability due to severe corrosion. Herein, we report the effective development of Fe₃C-based nanoparticles for electrochemical NH₃ synthesis, which features the strong bonding with carbon layers by controllable pyrolysis of an Fe-based coordination polymer (FeCP). It is revealed that the Fe₃C is partially transformed into Fe₃O₄ during the reaction, while the remaining Fe₃C is still chemically bonded with carbon layers through Fe─C bonds. The generated heterogeneous catalyst possesses optimized electronic structure, effectively facilitating the NO₃ ^- adsorption and subsequent protonation. Simultaneously, the Fe─C bonding interface is beneficial for suppressing the Fe leaching during the long-term testing, overcoming the intrinsic issue of Fe-based catalysts. The as-obtained catalyst shows a high Faradaic efficiency of 92.6% at -0.6 V (versus reversible hydrogen electrode, vs. RHE) and a high NH₃ yield rate of 17.7 mg h^-1 mg^-1 _cat., together with the stable operation within 96 h at -1.0 V vs. RHE. This study provides a facile strategy toward stabilizing iron-based electrocatalysts for cost-effective and sustainable NH₃ production.