Comparison between Fe₂O₃/C and Fe₃C/Fe₂O₃/Fe/C Electrocatalysts for N₂ Reduction in an Alkaline Electrolyte

Cost-effective and nonprecious iron-based catalysts were synthesized, evaluated, and compared for electrocatalytic N₂ reduction reaction (NRR) under alkaline conditions in the potential range from -0.4 to 0.1 V [vs reversible hydrogen electrode (RHE)] at low temperature (≤60 °C) and atmospheric pressure. The tested H-type cell was separated by an anion exchange membrane in 6 M KOH alkaline electrolyte (pH = over 14) in order to minimize hydrogen evolution reaction and to directly form NH₃ gas. The amount of ammonia synthesized was quantified using an indophenol blue method and cross-checked with ¹H nuclear magnetic resonance spectroscopy and ion chromatography using both ¹⁴N₂ and ¹⁵N₂ gases. Because of the synergistic effect between the Fe₃C, Fe₂O₃, and Fe composites in the NRR, both the ammonia formation rate and faradaic efficiency in Fe₃C/Fe₂O₃/Fe/C were approximately fourfold higher than those in Fe₂O₃/C at 60 °C and 0.1 V (vs RHE). These results can provide insights into designing Fe-based electrocatalysts for NRR at atmospheric pressure.