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Issue 6, 2019

Ammonia synthesis from nitrogen and water at intermediate temperatures and elevated pressures by using an electrochemical hydrogen-membrane reactor with supported Ru catalysts and phosphate electrolytes

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Abstract

Electrochemical synthesis of NH3 from N2 and H2O with electrical power is a promising technology to convert redundant electricity to a chemical fuel. NH3 synthesis from N2 and H2O using a combination of Cs-promoted Ru catalysts, a Pd-based hydrogen-membrane cathode, a CsH2PO4/SiP2O7 electrolyte, and a Pt anode was investigated in the temperature range of 200–250 °C and pressure range of 0.1–0.7 MPa. A maximum NH3 formation rate of 12.4 nmol s−1 cm−2 (759 μg h−1 cm−2) was obtained at 250 °C and 0.7 MPa using 5 wt%-Ru/Cs+/MgO (Cs/Ru = 1 mol) for a current density of 30 mA cm−2. The corresponding current efficiency for NH3 formation was estimated to be 12%, and the remaining part of the current was confirmed to be used for H2 production. The NH3 formation rate increased upon increasing the total pressure, following thermodynamic equilibrium. 5 wt%-Ru/Cs+/CeO2 (Cs/Ru = 1 atom) was found to yield the highest formation rate of NH3 at 200–220 °C and 0.1 MPa, while Ru/Cs+/MgO yielded a higher NH3 formation rate than Ru/Cs+/CeO2 under elevated pressure conditions. Because the dissociation of linearly adsorbed molecular N2 on Ru is known to be the rate-determining step in NH3 synthesis, infrared spectroscopy was utilized to examine the linearly adsorbed N2 on the Ru sites at the adsorption equilibrium at 30 °C.

Graphical abstract: Ammonia synthesis from nitrogen and water at intermediate temperatures and elevated pressures by using an electrochemical hydrogen-membrane reactor with supported Ru catalysts and phosphate electrolytes

Supplementary files

Article information


Submitted
24 Jan 2019
Accepted
12 Mar 2019
First published
13 Mar 2019

Sustainable Energy Fuels, 2019,3, 1406-1417
Article type
Paper
Author version available

Ammonia synthesis from nitrogen and water at intermediate temperatures and elevated pressures by using an electrochemical hydrogen-membrane reactor with supported Ru catalysts and phosphate electrolytes

K. Imamura and J. Kubota, Sustainable Energy Fuels, 2019, 3, 1406 DOI: 10.1039/C9SE00049F

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