Zinc–zinc oxide cycle

The Zn/ZnO 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[1] for hydrogen production[2] with a typical efficiency around 40%.[3]

## Process description

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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 1,900 °C (3,450 °F) into zinc and oxygen. In the second non-solar exothermic step zinc reacts at 427 °C (801 °F) 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

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

## References

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1. ^ Solar Hydrogen Production from a ZnO/Zn Thermo-chemical Cycle Archived July 24, 2008, at the Wayback Machine
2. ^ Project PD10
3. ^ Novel Method for solar hydrogen generation Archived February 5, 2009, at the Wayback Machine
4. ^ Solar thermal ZnO-decomposition

## External links

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