Zinc–zinc oxide cycle

For chemical reactions, the zinc–zinc oxide cycle or Zn–ZnO cycle is a two step thermochemical cycle based on zinc and zinc oxide for hydrogen production with a typical efficiency around 40%.

Process description
The thermochemical two-step water splitting process uses redox systems:


 * Dissociation: ZnO → Zn + 1/2 O2
 * Hydrolysis: Zn + H2O → ZnO + H2

For the first endothermic step concentrating solar power is used in which zinc oxide is thermally dissociated at 1900 °C into zinc and oxygen. In the second non-solar exothermic step zinc reacts at 427 °C with water and produces hydrogen and zinc oxide. The temperature level is realized by using a solar power tower and a set of heliostats to collect the solar thermal energy.