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.

Highly Selective Electrochemical Reduction of Dinitrogen to Ammonia at Ambient Temperature and Pressure over Iron Oxide Catalysts

“…An ammonia formation rate of 0.21 mgh À1 cm À2 and ac urrent efficiency of 0.28 %w ere observed at À1.1 Vv s. Ag/AgCl at 20 8C. [21] Later,t hey optimized the electrochemical system to achieveahigherN H 3 yield of 0.534 mgh À1 cm À2 by a3 0% Fe 2 O 3 -CNT catalyst in 0.5 m KOH at À2.0 Vv s. Ag/AgCl; [22] however,t he corresponding FE was very low (0.164 %). [20] Additionally,n on-precious-metal catalysts for the electrocatalytic reduction of N 2 to NH 3 are more desirable for practical applications owing to their abundance, low cost, and wide tunability of the structure-activity relationship.…”

“…Recently, the Centi group used an iron-based catalyst in aP EM cell with NaHCO 3 aqueous electrolyte, which achieved am aximum ammonia yield of 0.22 mgh À1 cm À2 at À2.0 Vv s. Ag/AgCl, but it showedavery limited NH 3 FE (< 0.05 %). [21] Later,t hey optimized the electrochemical system to achieveahigherN H 3 yield of 0.534 mgh À1 cm À2 by a3 0% Fe 2 O 3 -CNT catalyst in 0.5 m KOH at À2.0 Vv s. Ag/AgCl; [22] however,t he corresponding FE was very low (0.164 %). Recently,a nother study that used a g-Fe 2 O 3 catalyst was reported by Kong et al,w hicha chieved a maximum NH 3 yield of 0.783 mgh À1 cm À2 at 1.6 Vi naporous anion-exchange membranec ell.…”

Electrochemical Nitrogen Reduction Reaction on Noble Metal Catalysts in Proton and Hydroxide Exchange Membrane Electrolyzers

“…8 Although Nafion-based low temperature electrochemical ammonia synthesis has been demonstrated in several reports, [9][10][11][12][13][14][15] no systematic investigation of noble metal catalysts exists. 2 Further, the alkaline environment of hydroxide exchange membranes (HEMs) promises the employment of non-noble metal catalysts and no acid/base reaction between the produced ammonia and the membrane is expected.…”

Co‐generation of Ammonia and H2 from H2O Vapor and N2 Using a Membrane Electrode Assembly

“…In comparison to the works published by Lan et al , Skodra et al , Licht et al , and Chen et al , this work demonstrates an easy and at the same time highly efficient process for the electrochemical NH 3 synthesis. The introduced MEA and ecMR system have several advantages compared to reaction systems used in literature so far.…”