Research on the Spectra Characteristics and Catalysis Effects of Nanosized Ce0.95M0.05O2 (M=Fe, Nd, Eu) Solid Solutions
ZHANG Guo-fang1, HU Feng1, XU Jian-yi1, YU Hai-shu1, GE Qi-lu2, ZHANG Yang-huan1,2
1. School of Material and Metallurgy, Inner Mongolia University of Science and Technology, Baotou 014010, China
2. Department of Functional Material Research, Central Iron & Steel Research Institute, Beijing 100081, China
Abstract：Nanosized Ce0.95M0.05O2（M=Fe3+, Nd3+, Eu3+） solid solutions were synthesized via hydrothermal method. The micro-crystalline structure and spectra characteristics were investigated systemically. X-ray diffraction (XRD) results showed that doped samples exhibited single phase fluorite cubic structure，while no impurity phases corresponding to the doped ions oxides were observed. This result indicated that the doped ions had been doped into the lattice of CeO2 and formed solid solutions. The crystalline sizes of the samples were calculated lower than 20 nm. The electron transition properties of the solid solutions were characterized by UV-Vis spectra. Red-shift of absorption edges of the doped solid solutions was observed. Meanwhile, the band gap energies were fitted and it was found that the obtained values from large to small is CeO2 (3.13 eV)＞Ce0.95Eu0.05O2 (3.04 eV)＞Ce0.95Nd0.05O2 (2.94 eV)＞Ce0.95Fe0.05O2 (2.75 eV). The photoluminescence (PL) spectra displayed that the intensities of the doped sample emission peaks were lower than that of pure CeO2. Among them, the peak of the solid solution with Fe3+ ions possessed the lowest intensity. It can be explained that the doping of Fe3+ ions would introduce more defects in the lattice, which would hinder the recombination of electrons and holes. The solid solutions were added into Mg2Ni-Ni as catalysts and the Mg2Ni-Ni-5%Ce0.95M0.05O2 composites were obtained via ball milling method. The electrochemical and dynamic hydrogen storage performances were tested systematically. It was showed that the Ce0.95M0.05O2 solid solutions could improve the electrochemical discharge properties, the maximum discharge capacities were Ce0.95Fe0.05O2 (874.8 mA h·g-1) ＞Ce0.95Nd0.05O2 (827.8 mAh·g-1) ＞Ce0.95Eu0.05O2 (822.7 mA h·g-1) ＞CeO2 (764.9 mAh·g-1), respectively. Meanwhile, the catalysts also could enhance the electrochemical cycle stabilities of the composites effectively. The capacity retention ratio after 20 cycles were Ce0.95Fe0.05O2 (49.8%)＞Ce0.95Eu0.05O2 (49.7%)＞Ce0.95Nd0.05O2 (46.3%)＞CeO2 (34.1%). The high rate discharge (HRD) properties of the composites were characterized, and it was proved that the solid solutions catalysts could improve the large current discharge performances of the composites. For instance, when the discharge current density was 200 mAh·g-1, the HRD were Ce0.95Fe0.05O2 (59.5%)＞Ce0.95Eu0.05O2 (57.4%)＞ Ce0.95Nd0.05O2 (55.7%)＞CeO2 (54.4%). The influence of the catalysts on the H diffusion capacity in the composites was evaluated by constant potential step technique, and the H diffusion coefficient was: Ce0.95Fe0.05O2＞Ce0.95Eu0.05O2＞Ce0.95Nd0.05O2＞CeO2. The catalysis effects of the solid solutions were closely related to the concentration of oxygen vacancies, lattice defects in the lattice and the characteristic of easy to change valences of the doped ions.
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