Electrochemical Synthesis of NH₃ at Low Temperature and Atmospheric Pressure Using a γ-Fe₂O₃ Catalyst

The electrochemical synthesis of NH₃ by the nitrogen reduction reaction (NRR) at low temperature (<65 °C) and atmospheric pressure using nanosized γ-Fe₂O₃ electrocatalysts were demonstrated. The activity and selectivity of the catalyst was investigated both in a 0.1 M KOH electrolyte and when incorporated into an anion-exchange membrane electrode assembly (MEA). In a half-reaction experiment conducted in a KOH electrolyte, the γ-Fe₂O₃ electrode presented a faradaic efficiency of 1.9% and a weight-normalized activity of 12.5 nmol h^-1 mg^-1 at 0.0 V_RHE. However, the selectivity toward N₂ reduction decreased at more negative potentials owing to the competing proton reduction reaction. When the γ-Fe₂O₃ nanoparticles were coated onto porous carbon paper to form an electrode for a MEA, their weight-normalized activity for N₂ reduction was found to increase dramatically to 55.9 nmol h^-1 mg^-1. However, the weight- and area-normalized N₂ reduction activities of γ-Fe₂O₃ decreased progressively from 35.9 to 14.8 nmol h^-1 mg^-1 and from 0.105 to 0.043 nmol h^-1 cm^-2_act, respectively, during a 25 h MEA durability test. In summary, a study of the fundamental behavior and catalytic activity of γ-Fe₂O₃ nanoparticles in the electrochemical synthesis of NH₃ under low temperature and pressure is presented.