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.
CeO2-MOx (M = Mn, Fe, Ni, Cu) reactive ceramics, having high melting points and high conductivities of O2−, were synthesized with the combustion method from their nitrates for solar hydrogen production. The prepared CeO2-MOx samples were solid solutions between CeO2 and MOx with the fluorite structure through XRD. Two-step water splitting reactions with CeO2-MOx reactive ceramics proceeded at 1573–1773K for the O2 releasing step and at 1273K for the H2 generation step by irradiation of infrared imaging furnace as a solar simulator. The amounts of O2 evolved in the O2 releasing reaction with CeO2-MOx and CeO2 systems increased with the increase of the reaction temperature. The amounts of H2 evolved in the H2 generation reaction with CeO2-MOx systems except for M = Cu were more than that of CeO2 system after the O2 releasing reaction at the temperatures of 1673 and 1773K. The largest amount of H2 was generated with CeO2-NiO after the O2 releasing reaction at 1573, 1673 and 1773K. The O2 releasing reaction at 1673K and H2 generation reaction at 1273K with CeO2-Fe2O3 were repeated four times with the evolving of O2 (1.3cm3/g-sample) and H2 (2.3cm3/g-sample) gases, respectively. The possibility of solar hydrogen production with CeO2-MOx (M = Mn, Fe, Ni) reactive ceramics system by using concentrated solar thermal energy was suggested.
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