O_2-releasing reactivity of ceria-based reactive ceramics on irradiation of artificial concentrated solar beam for solar hydrogen production

摘要

In the present paper, different types of metal doped ceria CeO_2-MO_x (M = Sc, Y, Dy, Zr and Hf) with fluorite structure have been prepared with a complex polymerization method. The O_2-releasing potential of prepared samples was evaluated at 1500 ℃ for a two-step water splitting process. The partially oxygen defected CeO_2-MO_(1.5) (M = Sc~(3+), Y~(3+) or Dy~(3+)) mixed oxide exhibited an enhancement of the O_2 evolution on CeO_2-ScO_(1.5) owing to the crystal-chemical effect that cation with smaller ionic radius (Sc~(3+)) compensates the volume expansion of crystal lattice resulted in the reduction of Ce~(4+) with smaller ionic radius into Ce~(3+) with larger ionic radius. The CeO_2-MO_2 (M = Zr~(4+) and Hf~(4+)) produced larger amount of O_2 than that for CeO_2-MO_(1.5) mixed oxides, since CeO_2-MO_2 has no oxygen vacancy initially. While the ionic radii of Zr~(4+) and Hf~(4+) are almost equal, the higher O_2-releasing reactivity of Ce_(0.9)Hf_(0.1)O_2 than that of Ce_(0.9)Zr_(0.1)O_2 is explained in terms of ionicity of M-O bond. Also, the weight losses of CeO_2, Ce_(0.9)Zr_(0.1)O_2 and Ce_(0.9)Hf_(0.1)O_2 in the mitigation process from high P_(o_2) (O_2 gas stream) to low P_(o_2) (Ar gas stream) atmosphere were determined. The quasi activation energies in the initial period of the O_2-release for CeO_2, Ce_(0.9)Zr_(0.1)O_2 and Ce_(0.9)Hf_(0.1)O_2 were evaluated 105, 84.2 and 75.0 kJ/mol, respectively. The O_2-releasing reactivity is considered from the standpoint of an activation energy.