Improved electrolysis of liquid ammonia for hydrogen generation via ammonium salt electrolyte and Pt/Rh/Ir electrocatalysts

摘要

Liquid ammonia electrolysis is conducted out at ambient temperature using different ammonium salt electrolytes with and without the reference electrode. It is determined that electrolytes containing NH4+ increase the current density and reduce the solution resistance. Moreover, ammonium salts of NH4Br, NH4NO3 and NH4Cl preserve >80% current efficiency and a 0.6-0.8 mL min(-1) average rate of H-2 generation during chronopotentiometry tests at 120 mA cm(-2) for 3 h. A minimum electrolysis voltage (E-min) of ca. 1.2 V is required for the NH4Cl electrolyte when using Pt-foil as the anode and cathode. To decrease the overpotential of the anode reaction, five types of electrocatalysts were prepared and characterized: Pt-black, Rh, Pt-Ir, Rh-Pt and Ph-Pt-Ir alloys. Trimetallic Rh-Pt-Ir and bimetallic Pt-Ir, Rh-Pt (1:1) alloy electrodes exhibit a combined benefit of better activity and minimized deactivation. The ternary Rh-Pt-Ir alloy anode shows the best electrocatalytic activity with the lowest E-min of ca. 0.47 V and highest current density of 46.9 mA cm(-2) at 2.0 V. In comparison with the Pt-foil anode, the E-min is reduced by two-thirds, and the current density is increased two-fold. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.