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

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 NH 4 + increase the current density and reduce the solution resistance. Moreover, ammonium salts of NH 4 Br, NH 4 NO 3 and NH 4 Cl 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 NH 4 Cl 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.