O₂ Releasing Reactivity of Ceria-Based Reactive Ceramics on Irradiation of Concentrated Solar Beam for Solar Hydrogen Production

In the present paper, different types of metal doped ceria CeO₂-MO_x (M = Sc, Y, Dy, Zr and Hf) with fluorite structures have been prepared with a complex polymerization method. The O₂-releasing potential of prepared samples was evaluated at 1773 K for two-step water splitting process. The partially oxygen defected CeO₂-MO_1.5 mixed oxides (M = Sc³⁺, Y³⁺ and Dy³⁺) exhibited an enhancement of the O₂ evolution due to the crystal-chemical effect that cation with smaller ionic radius (Sc³⁺, Y³⁺ and Dy³⁺) mitigate the volume expansion of crystal lattice resulted in the reduction of Ce⁴⁺ with smaller ionic radius into Ce³⁺ with larger ionic radius. The CeO₂-MO₂ (M = Zr⁴⁺ and Hf⁴⁺) produced larger amount of O₂ than that for CeO₂-MO_1.5 mixed oxides, since CeO₂-MO₂ has no oxygen vacancy. While the ionic radii of Zr⁴⁺ and Hf⁴⁺ are almost equal, the higher O₂-releasing reactivity of Ce_0.9Hf_0.1O₂ than that of Ce_0.9Zr_0.1O₂ is explained in terms of ionicity of M-O bond. Thus, it was found that both ionic radius and ionicity play important role in the O₂-releasing reaction.