Direct electrolysis of liquid anhydrous ammonia for continuous production of high-purity, pressurized hydrogen at ambient temperature†

The direct electrolysis of liquid anhydrous ammonia (NH₃(l), >99.99% of NH₃, free of water and solvent) is demonstrated using a 25 cm² zero-gap electrolyzer, consisting of a Ru/C anode and a Pt/C cathode, with the two electrodes spatially separated by a cation exchange membrane. This system, supplied by NH₃(l) and NH₄Br as the supporting electrolyte, continuously produces high-purity and pressurized hydrogen (H₂, >99.99%, >5.5 bar) at a temperature of 10 °C and a pressure of 6.2 bar, without requiring H₂/N₂ separation and compression processes. The direct NH₃(l) electrolyzer exhibits a cell potential of 1.1 V at 0.1 A cm⁻², presenting a faradaic efficiency of >99.3% for H₂ production. The developed system achieves a H₂ production rate of >18.8 mol-H₂ g_cat⁻¹ h⁻¹ at 0.5 A cm⁻², which is 4.7-fold higher than the highest H₂ production rate reported to date for NH₃(g) thermolysis at temperatures of over 500 °C.