Effect of Temperature and H Flux on the NH₃ Synthesis via Electrochemical Hydrogen Permeation

Abstract

Ammonia is an indispensable commodity and a potential carbon free energy carrier. The use of H permeable electrodes to synthesize ammonia from N
₂, water and electricity, provides a promising alternative to the fossil fuel based Haber-Bosch process. Here, H permeable Ni electrodes are investigated in the operating temperature range 25–120 °C, and varying the rate of electrochemical atomic hydrogen permeation. At 120 °C, a steady reaction is achieved for over 12 h with 10 times higher cumulative NH
₃ production and almost 40-fold increase in faradaic efficiency compared to room temperature experiments. NH
₃ is formed with a cell potential of 1.4 V, corresponding to a minimum electrical energy investment of 6.6 kWh kg
⁻¹ (Figure presented.). The stable operation is attributed to a balanced control over the population of N, NH
_x and H species at the catalyst surface. These findings extend the understanding on the mechanisms involved in the nitrogen reduction reaction and may facilitate the development of an efficient green ammonia synthesis process.