This study describes the experiment of thermochemical splitting of carbon dioxide using the redox reaction of nonstoichiometric compound, ceria and hercynite (generally iron aluminate, Fe₃₃Al₆₇, in Fe-Al-O space). The reactive foam devices of ceria and hercynite were sintered through the replica method. The devices were kept in the receiver reactor, and they were irradiated by the concentrated light from the sun simulator. The temperature at the reduction process was changed up to beyond 1600℃. In the non-isothermal experiment, the temperature control with holding near the peak level increased the reaction in the case using ceria as reactive material. In the isothermal experiment, the reaction of hercynite is relatively slow compared with that of ceria. However, the change in nonstoichiometry of hercynite surpassed that of ceria. It was indicated that hercynite released twice as much gas as ceria of the same mass.