Zinc–zinc oxide cycle explained

For chemical reactions, the zinc–zinc oxide cycle or Zn–ZnO cycle is a two step thermochemical cycle based on zinc and zinc oxide^[1] for hydrogen production^[2] with a typical efficiency around 40%.^[3]

Process description

The thermochemical two-step water splitting process uses redox systems:^[4]

• 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.

See also

• Cerium(IV) oxide–cerium(III) oxide cycle
• Copper–chlorine cycle
• Hydrosol-2
• Hybrid sulfur cycle
• Iron oxide cycle
• Sulfur–iodine cycle

External links

• H2 formation by zinc hydrolysis in a hot wall aerosol flow reactor

Notes and References

1. http://www.solarpaces.org/Tasks/Task2/SHP.HTM Solar Hydrogen Production from a ZnO/Zn Thermo-chemical Cycle
2. http://www.hydrogen.energy.gov/pdfs/review06/pd_10_weimer.pdf Project PD10
3. http://www.switt.ch/files/technologien/Solar%20Hydrogen%20Production_04-014.pdf Novel Method for solar hydrogen generation
4. https://web.archive.org/web/20060505180329/http://solar.web.psi.ch:80/data/research/zno/roca/ Solar thermal ZnO-decomposition