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.