Electrochemical-catalytic NH3 synthesis from H2O and N2 using an electrochemical cell with a Ru catalyst, Pd–Ag membrane cathode, and NaOH–KOH molten salt electrolyte at 250 °C

Abstract

Using sustainable energy-based electricity to synthesize NH₃ from H₂O and N₂ to release O₂ not only contributes to making chemical fertilizer production carbon neutral, but also holds promise for the use of NH₃ as a fuel. NH₃ synthesis from water and nitrogen was conducted at around 250 °C and below 1.0 MPa by combining a molten salt electrolyte of NaOH–KOH, a Pd alloy hydrogen-permeable membrane cathode, a Ni anode, and a Ru-based catalyst on the cathode backside. The rate and current efficiency for NH₃ formation were obtained as 11 nmol s⁻¹ cm⁻² (38 μmol h⁻¹ cm⁻²) and 25%, respectively, at 30 mA cm⁻², 1.0 MPa, and 250 °C. It was confirmed that the remaining percentage from the 100% current efficiency for NH₃ production was attributed to the current efficiency for H₂ production. The cell voltage was as low as 1.47 V at 30 mA cm⁻² and increased to 1.95 V at 100 mA cm⁻². The potential of this electrochemical system is discussed.