Electrocatalytic Synthesis of Ammonia at Room Temperature and Atmospheric Pressure from Water and Nitrogen on a Carbon-Nanotube-Based Electrocatalyst

Abstract

Ammonia is synthesized directly from water and N₂ at room temperature and atmospheric pressure in a flow electrochemical cell operating in gas phase (half-cell for the NH₃ synthesis). Iron supported on carbon nanotubes (CNTs) was used as the electrocatalyst in this half-cell. A rate of ammonia formation of 2.2×10^-3 gNH3 m^-2 h^-1 was obtained at room temperature and atmospheric pressure in a flow of N₂ , with stable behavior for at least 60 h of reaction, under an applied potential of -2.0 V. This value is higher than the rate of ammonia formation obtained using noble metals (Ru/C) under comparable reaction conditions. Furthermore, hydrogen gas with a total Faraday efficiency as high as 95.1 % was obtained. Data also indicate that the active sites in NH₃ electrocatalytic synthesis may be associated to specific carbon sites formed at the interface between iron particles and CNT and able to activate N₂ , making it more reactive towards hydrogenation.

Keywords: ammonia; atmospheric pressure; carbon nanotubes; electrochemistry; heterogeneous catalysis.