Comparison between Fe 2 O 3 /C and Fe 3 C/Fe 2 O 3 /Fe/C Electrocatalysts for N 2 Reduction in an Alkaline Electrolyte.

Cost-effective and nonprecious iron-based catalysts were synthesized, evaluated, and compared for electrocatalytic N 2 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 NH 3 gas. The amount of ammonia synthesized was quantified using an indophenol blue method and cross-checked with 1 H nuclear magnetic resonance spectroscopy and ion chromatography using both 14 N 2 and 15 N 2 gases. Because of the synergistic effect between the Fe 3 C, Fe 2 O 3 , and Fe composites in the NRR, both the ammonia formation rate and faradaic efficiency in Fe 3 C/Fe 2 O 3 /Fe/C were approximately fourfold higher than those in Fe 2 O 3 /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.