Ding Rong Ou

Microstructural and Metal-Support Interactions of the Pt-CeO2/C Catalysts for Direct Methanol Fuel Cell Application

To understand the ceria promotion effect of Pt-CeO(2)/C catalysts on methanol oxidation, microstructural and metal-oxide interactions of Pt-CeO(2)/C catalysts with an atomic ratio of Pt/Ce between 0.14 and 1.4 were systematically examined using high-resolution transmission electron microscopy and electron energy loss spectroscopy (EELS). With an increasing Pt content in the catalysts, Pt particles gradually invaded into the ceria supports and decoration on Pt particles was observed. Simultaneously, the morphology of the supports was dramatically modified with nanocrystalline and amorphous ceria formed between and/or around the Pt particles. It reveals that the Pt-ceria interaction could take place in the catalysts and the influence of the interaction was enhanced with an increasing Pt/Ce ratio. The EELS study demonstrated that the strong Pt-ceria interaction was related to the redox reaction between Pt and ceria. Experimental results also suggested that the strong interaction between Pt and ceria could contribute to the promotion effect of ceria on the oxidation of methanol.

Oxygen vacancy ordering in heavily rare-earth-doped ceria

25 at. % Rare-earth (RE)-doped ceria samples (RE=Sm, Dy, Y, and Yb) were examined using transmission electron microscopy and electron energy loss spectroscopy, from which the oxygen vacancy ordering in nanosized domains was confirmed. The relationships of the dopant type, oxygen vacancy ordering, and ionic conductivity of doped ceria were established. It is found that the ordering of oxygen vacancies depends strongly on the dopant type, and the development of nanosized domains with a higher degree of ordering can lead to a more dramatic decrease of ionic conductivity in doped ceria. (c) 2006 American Institute of Physics.

Evidence of Intragranular Segregation of Dopant Cations in Heavily Yttrium-Doped Ceria

The intragranular segregation of dopant cations in 25 atom % yttrium- doped ceria was explored by energy filtering transmission electron microscopy. Through the comparison between samples sintered at different temperatures, the correlation between the intragranular segregation of dopant cations and the formation of nanosized domains in heavily doped ceria is clearly shown. It is suggested that the segregation can lead to the domain formation, and the oxygen vacancies may also segregate into the domains with the dopant cations. (c) 2006 The Electrochemical Society.

Compositional and valent state inhomogeneities and ordering of oxygen vacancies in terbium-doped ceria

Intragranular distributions of composition and valent state in sintered Tb-doped ceria have been systematically investigated. Through detailed studies of electron energy loss spectroscopy and energy filtering transmission electron microscopy, both compositional and valent state inhomogeneities of Ce and Tb were confirmed, which are related to the existence of nanosized domains in Tb-doped ceria. Compared with their matrix, the domains have higher Tb concentration and Ce and Tb cations in the domains tend to be trivalent. Furthermore, ordering of oxygen vacancies in the domains, which increases with increasing doping concentration, has been determined by EELS.

Ionic Conductivities and Microstructures of Ytterbium-Doped Ceria

The ionic conductivities and microstructures of Ce1-xYbxO2-x/2 ( x = 0.10, 0.15, 0.20, and 0.25 ) with average grain sizes in a range of 0.2 - 3.7 mu m were studied systematically. Nanosized domains were confirmed through detailed studies of transmission electron microscopy. The relationships of the domains, doping concentration, and grain size were determined, and their effects on the ionic conductivities were examined. It was concluded that the domains were formed via the segregation of Yb cations so that they could trap the oxygen vacancies and lower the conductivity. Furthermore, the development of the domains, which depends on the doping concentration and grain size, can affect the doping concentration and grain-size dependencies of the conductivity. (c) 2006 The Electrochemical Society.

Improvement of Cathode Performance on Pt-CeOx by Optimization of Electrochemical Pretreatment Condition for PEFC Application

Pt-CeO(x)/C electrocatalysts for the improvement of oxygen reduction reaction (ORR) activity on cathode were prepared by a combined process of precipitation and co-impregnation methods. The Pt-CeO(x)/C electrocatalysts pretreated by the optimized electrochemical conditioning process showed high ORR activity as compared with homemade Pt/C electrocatalyst. Also, it showed high stability in the cyclic voltammetry (CV) test up to 1000 cycles into 0.5 M H(2)SO(4) aqueous solution. On the basis of the data of cyclic voltammogram of 30 cyclic sweeps, X-ray photoelectron spectroscopy, electron energy loss spectroscopy, high resolution transmission electron microscope image, and selected area electron diffraction analysis, it is concluded that the Pt-CeO(x) heterointerface involving the defect cluster formed by using optimized electrochemical pretreatment conditions on Pt in Pt-CeO(x)/C electro-catalyst contributes to the promotion of ORR activity and retention of its stability in long CV tests up to 1000 cycles.

Microstructural Inhomogeneity in Holmium-Doped Ceria and Its Influence on the Ionic Conduction

Inhomogeneous microstructures, including nanosized domains and nanoprecipitates, were observed in sintered samples of holmium-doped ceria. The formation of such microstructural inhomogeneity is related to the segregation of dopant cations and can be enhanced by increasing doping concentration and sintering temperature. Through examination of the relationship between the microstructures and electrical properties, it was found that the inhomogeneity can have negative impacts on ionic conduction, which could be explained in terms of the interaction between the oxygen vacancies and the segregated dopant cations

Defect clustering and local ordering in rare earth co-doped ceria

Defect clustering and local ordering in rare earth co-doped ceria were studied by computer simulation and electron diffraction, respectively. The simulation of electrically neutral defect clusters containing up to four oxygen vacancies revealed that the permutation of different dopant cations in a co-doped cluster could have a significant influence on the binding energy of the cluster. Moreover, the growth of larger clusters (number of oxygen vacancies ≥ 3) could be restrained by a co-doping effect. The selected area electron diffraction study indicated that the restrained growth of larger clusters will further lead to a suppression of the local ordering of oxygen vacancies in co-doped ceria. The correlation between defect clustering, local ordering of oxygen vacancies and ionic conduction in co-doped ceria was discussed.

Microstructural Characteristics of SDC Electrolyte Film Supported by Ni–SDC Cermet Anode

As a promising electrolyte material for intermediate-temperature solid oxide fuel cells operated at a temperature of <= 600 degrees C, a Sm0.2Ce0.8O1.9 (SDC) film supported by a Ni-SDC cermet anode was prepared through electrophoretic deposition. Detailed microstructural features of the electrolyte film were studied. In the region away from the interface, the microstructure of the SDC film is similar to that of the SDC bulk sample, containing nanosized domains embedded in a fluorite matrix. However, in the region near the interface, the diffusion of Ni from the cermet anode to the electrolyte film was observed with a depth of about 1 mu m. Furthermore, the reduction in Ce and a high degree of oxygen vacancy ordering can be noticed in the interfacial region at the electrolyte side. It is suggested that these microstructural features could have negative impacts on the ionic conductivity of the electrolyte films.

Approach for imaging optical super-resolution based on Sb films

Super-resolution technology has been applied to overcome the optical diffraction limit in recent years. In this work, optical super resolution based on Sb films has been studied. Experimental results show that the amorphous Sb–SR will considerably concentrate the energy into the center of the laser beam, while the crystal Sb–SR will not. Considering Sb as a semiconductor with a small energy gap, a three-order nonlinear response of surface plasmons is deduced to explain the phenomenon. Estimation is made and the calculated results are in agreement with the experimental results.