Iron Oxide Cycle - Hercynite Cycle

Hercynite Cycle

Like the traditional iron oxide cycle, the hercynite is based on the oxidation and reduction of iron atoms. However unlike the traditional cycle, the ferrite material reacts with a second metal oxide, aluminum oxide, rather than simply decomposing. The reactions take place via the following two reactions:

(1) M(II)Fe₂(III)O₄ + 3Al₂O₃ → M(II)Al₂(III)O₄ + 2Fe(II)Al₂(III)O₄ + ½O₂ (Reduction)

(2) M(II)Al₂(III)O₄ + 2Fe(II)Al₂(III)O₄ + H₂O → M(II)Fe₂(III)O₄ + 3Al₂O₃ + H₂ (Oxidation)

The reduction step of the hercynite reaction takes place at temperature ~ 200 oC lower than the traditional water splitting cycle ( 1200 oC). This leads to lower radiation losses, which scale as temperature to the fourth power.