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

Abstract

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 an 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.