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

Abstract

The electrochemical synthesis of NH3 by the nitrogen reduction reaction (NRR) at low temperature (<65 degrees C) and atmospheric pressure using nanosized gamma-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 gamma-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. However, the selectivity toward N-2 reduction decreased at more negative potentials owing to the competing proton reduction reaction. When the gamma-Fe2O3 nanoparticles were coated onto porous carbon paper to form an electrode for a MEA, their weight-normalized activity for N-2 reduction was found to increase dramatically to 55.9 nmol h(-1) mg(-1). However, the weight- and area-normalized N-2 reduction activities of gamma-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 gamma-Fe2O3 nanoparticles in the electrochemical synthesis of NH3 under low temperature and pressure is presented.