Iron oxide cycle

The steps of solar hydrogen production by iron based two-step cycle are: Where M can by any number of metals, often Fe itself, Co, Ni, Mn, Zn or mixtures thereof.

The oxidative water splitting step (2) occurs at a lower ~1000 °C temperature which produces the original ferrite material in addition to hydrogen gas.

[3] This leads to lower radiation losses, which scale as temperature to the fourth power.

The advantages of the ferrite cycles are: they have lower reduction temperatures than other 2-step systems, no metallic gasses are produced, high specific H2 production capacity, non-toxicity of the elements used and abundance of the constituent elements.

The disadvantages of the ferrite cycles are: similar reduction and melting temperature of the spinels (except for the hercynite cycle as aluminates have very high melting temperatures), and slow rates of the oxidation, or water splitting, reaction.