Thermogravimetric analysis of the ZnO/Zn water splitting cycle

The endothermal dissociation of zinc oxide into its elements, followed by the exothermal hydrolysis of zinc, is considered as a two-step water splitting thermochemical cycle using high-temperature solar process heat. Thermogravimetric measurements were conducted on both reaction steps to elucidate the influence of temperature, oxygen partial pressure, inert gas flow rate, and chemical impurities on the reaction kinetics. The dissociation rate increased with the temperature and mass flow rate of an inert gas, and decreased with the oxygen concentration in the inert gas. The hydrolysis reaction proceeded faster for molten zinc and for zinc-containing impurities, but a layer of ZnO prevented reaching completion. The implications on the reactor design are discussed briefly.