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

Abstract

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 VRHE. 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. © 2017 American Chemical Society