The rotary-type solar reactor has been developed and fabricated for solar hydrogen production by a two-step water-splitting process using the reactive ceramics of CeO2 and Ni,Mn-ferrite (Ni0.5Mn0.5Fe2O4). It has a cylindrical rotor and dual cells for discharging O2 and for the H2O splitting reaction. A detailed specification and the efficiency of the rotary-type solar reactor were examined for the two-step water-splitting process. The maximum temperature of the reactive ceramics mounted on the cylindrical rotor was ca. 1623 K by irradiation with a solar simulator of an infrared imaging lamp. Repetition of the two-step water-splitting process using the rotary-type solar reactor with CeO2 was achieved, and successive evolution of H2 was observed in the H2O-splitting reaction cell at the optimum reaction temperatures of the O2-releasing reaction cell (T = 1623 K) and H2O-splitting reaction cell (T = 1273 K). Also, repetition of the two-step water-splitting process was achieved in the case of using the reactive ceramics of Ni,Mn-ferrite, and its optimum reaction temperatures of the O2-releasing and H2-generation reactions were 1473 and 1173 K, respectively. It was confirmed that the higher O2-releasing reaction temperature of above 1800 K was achieved with the about 10-times scaled-up rotary-type solar reactor.

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The two-step water splitting with the solid solution of YSZ (Yttrium stabilized Zirconia) and Ni-ferrite (NiFe2O4) was studied for solar hydrogen production. The sample of YSZ/Ni-ferrite solid solution was prepared by calcination of the mixture of the YSZ balls and Ni-ferrite (NiFe2O4) powder. The two-step water splitting process composed of O2-releasing reaction (T = 1773K) in Ar gas flow and H2-generation reaction (T = 1473K) in Ar gas and steam flow with the YSZ/Ni-ferrite solid solution were repeated ten times, and the molar ratio of the released O2 gas and the generated H2 gas was nearly equal to 1:2 in each cycle, indicating that the two-step water splitting process proceeded stoichiometrically. The lattice constants of the YSZ/Ni-ferrite solid solution products after each step of the water splitting process were varied, therefore it was assumed that the oxidation and reduction of the iron ions proceeded in the YSZ phase. It is confirmed that the YSZ/Ni-ferrite was the solid solution and reactive ceramics of high thermal stability. The contents of iron ions determined by the atomic absorption spectroscopy indicated that the YSZ/Ni-ferrite solid solution heated at 1773K contained the only 36% of iron loaded initially. The generated O2 gas was 42% of the theoretical yield. These suggest that YSZ/Ni-ferrite solid solution is more effective reactive ceramics which has the ability to split water with concentrated solar heat than Ni-ferrite.

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