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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 reactive ceramics suitable for the rotary-type solar reactor (proposed by Tokyo Institute of Technology, Tokyo) with two-step water-splitting reaction were developed. It is confirmed that O2 gas is evolved in the two-step water-splitting reaction with the reactive ceramics vigorously by rapid heating (α-O2-releasing reaction). The α-O2-releasing reaction is due to the formation of interstitial defect and the conversion of lattice oxygen into O2 gas at a nonequilibrium state. Reactive ceramics (NiFe2O4 and yttria stabilized zirconia (YSZ)-NiFe2O4 solid solution) can absorb solar thermal energy and convert thermal energy into chemical energy under high O2 partial pressure atmosphere in the α-O2-releasing reaction. Repetitive evolutions of O2 gas were observed in the two-step water-splitting reaction with YSZ-Fe3O4 solid solution and cerium based metal oxides (CeO2–NiO, CeO2–ZrO2, and CeO2–Ta2O5) at high O2 partial pressure. The CeO2–Ta2O5(Ce:Ta=90:10) released a large amount of O2 gas (3.95 cm3/g) in the α-O2 releasing reaction in the flow of air.