Two-step water splitting with Zn/Fe
3O
4 - ZnFe
2O
4 reaction system is suggested for H
2 generation to utilize concentrated solar heat. When mixture of Zn and Fe
3O
4 was heated to 873 K and steam was passed through, the H
2 was obtained in 93.4% of the theoretical yield. Formation of ZnFe
2O
4 with several zinc content (Zn
xFe
3-xO
4; 0.2≤x≤l) and ZnO was determined by XRD and Mössbauer spectroscopy. The yield of ZnO was 26-29%, which shows the ratio of the competition-reaction (H
2O Zn system) effects less in the total H
2 yield. O
2 generation (also energy storage) step can be proceeded at the temperature of ca. 1800 K. The reaction took place very fast, and it can be seen that a large amount of O
2 was released from irradiated ZnFe
2O
4. The stoichiometry and the reaction mechanism of the system are discussed upon the analyses for the solid product.
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