纳米Ce(0.95)M(0.05)O2(M=Fe,Nd,Eu)光谱特征及其催化性能研究

Research on the Spectra Characteristics and Catalysis Effects of Nanosized Ce0.95M0.05O2(M=Fe,Nd,Eu)Solid Solutions

采用水热法制备纳米Ce(0.95)M(0.05)O2(M=Fe^3+,Nd^3+,Eu^3+)固溶体,系统研究了固溶体的微观晶体结构及光谱特性。X射线衍射(XRD)结果表明,掺杂样品均为单相萤石立方结构,无对应于掺杂离子氧化物的杂相存在,说明三种掺杂离子均成功掺入CeO2晶格内而形成固溶体。计算各样品的晶粒尺寸,得到掺杂固溶体的粒度均低于20 nm。采用紫外可见光谱(UV-Vis)表征固溶体的电子跃迁性能。与纯CeO2相比,掺杂固溶体的吸收边均发生红移;同时,拟合得到各样品能隙由大到小依次为:CeO2(3.13 eV)>Ce(0.95)Eu(0.05)O2(3.04 eV)>Ce(0.95)Nd(0.05)O2(2.94 eV)>Ce(0.95)Fe(0.05)O2(2.75 eV)。荧光光谱(PL)测试表明,掺杂样品的发射峰强度均比纯CeO2低,其中Fe^3+掺杂固溶体样品的荧光强度降低最为明显。其原因在于Fe^3+掺杂会使固溶体晶格内引入更多缺陷,从而阻碍了电子与空穴的复合。将固溶体作为催化剂添加到Mg2Ni-Ni中,球磨制得Mg2Ni-Ni-5%Ce(0.95)M(0.05)O2复合材料,系统测试复合材料电极的电化学和动力学储氢性能。结果表明, Ce(0.95)M(0.05)O2固溶体可有效提高Mg2Ni-Ni合金复合材料的电化学放电性能,最大放电容量分别为:Ce(0.95)Fe(0.05)O2(874.8 mAh·g^-1)>Ce(0.95)Nd(0.05)O2(827.8 mAh·g^-1)>Ce(0.95)Eu(0.05)O2(822.7 mAh·g^-1)>CeO2(764.9 mAh·g^-1)。同时,催化剂还可有效提高复合材料的电化学循环稳定性,经20次循环后的容量保持率为:Ce(0.95)Fe(0.05)O2(49.8%)>Ce(0.95)Eu(0.05)O2(49.7%)>Ce(0.95)Nd(0.05)O2(46.3%)>CeO2(34.1%)。对复合材料进行高倍率放电性能(HRD)表征,掺杂固溶体催化剂能够显著提高样品的大电流放电性能,如当放电电流密度为200 mAh·g^-1时,各样品的HRD为:Ce(0.95)Fe(0.05)O2(59.5%)>Ce(0.95)Eu(0.05)O2(57.4%)>Ce(0.95)Nd(0.05)O2(55.7%)>CeO2(54.4%)。采用恒电位阶跃测试催化剂对复合材料中H扩散能力的影响, H扩散系数由大到小依次为Ce(0.95)Fe(0.05)O2>Ce(0.95)Eu(0.05)O2>Ce(0.95)Nd(0.05)O2>CeO2。分析认为,固溶体的催化效果与其氧空位浓度、晶格缺陷及掺杂离子易变价特性密切相关。

Nanosized Ce0.95M0.05O2(M=Fe^3+,Nd 3+,Eu 3+)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)>Ce0.95Eu0.05O 2(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 Fe^3+ions possessed the lowest intensity.It can be explained that the doping of Fe^3+ions would introduce more defects in the lattice,which would hinder the recombination of electrons and holes.The solid solutions were added into Mg 2Ni-Ni as catalysts and the Mg 2Ni-Ni-5%Ce0.95 M0.05O2 composites were obtained via ball milling method.The electrochemical and dynamic hydrogen storage performances were tested systematically.It was showed that the Ce 0.95 M 0.05 O 2 solid solutions could improve the electrochemical discharge properties,the maximum discharge capacities were Ce0.95Fe0.05O2(874.8 mA h·g^-1)>Ce 0.95 Nd 0.05 O 2(827.8 mAh·g^-1)>Ce 0.95 Eu 0.05 O 2(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.