Electrochemical fabrication of spherical zinc fuel balls and their utilization as safe alternatives to hydrogen

Abstract We proposed a power-to-zinc (P2Z) system in which electrochemically fabricated spherical zinc fuel balls are used as a safe, storable, and renewable alternative to hydrogen-based energy carriers. We found that the electrochemically produced zinc can be controlled to a spherical shape through the use of metal spheres as the core material. For these zinc fuel balls, the following processes were analyzed: (1) direct discharge in a zinc–air cell, and (2) hydrogen and power generation via a polymer electrolyte membrane fuel cell. The discharge capacity approached the theoretical value for zinc (800 mAh g −1 ), and a volumetric energy density up to 2.2 kWh l −1 was achieved. When employed as a 25 wt% slurry with 7 mol l −1 KOH, a volumetric energy density of 0.97 kWh l −1 could be maintained, which is comparable to the value for compressed hydrogen. The fuel balls exhibited excellent stability, recyclability, and flowability. The results indicate that spherical zinc balls are promising energy carriers and that the P2Z system could be applied as a safe renewable energy storage system.