High Performance Low-Temperature Solid Oxide Fuel Cells Based on Nanostructured Ceria-Based Electrolyte

Ceria based electrolyte materials have shown potential application in low temperature solid oxide fuel cells (LT-SOFCs). In this paper, Sm3+ and Nd3+ co-doped CeO2 (SNDC) and pure CeO2 are synthesized via glycine-nitrate process (GNP) and the electro-chemical properties of the nanocrystalline structure electrolyte are investigated using complementary techniques. The result shows that Sm3+ and Nd3+ have been successfully doped into CeO2 lattice, and has the same cubic fluorite structure before, and after, doping. Sm3+ and Nd3+ co-doped causes the lattice distortion of CeO2 and generates more oxygen vacancies, which results in high ionic conductivity. The fuel cells with the nanocrystalline structure SNDC and CeO2 electrolytes have exhibited excellent electrochemical performances. At 450, 500 and 550 °C, the fuel cell for SNDC can achieve an extraordinary peak power densities of 406.25, 634.38, and 1070.31 mW·cm−2, which is, on average, about 1.26 times higher than those (309.38, 562.50 and 804.69 mW·cm−2) for pure CeO2 electrolyte. The outstanding performance of SNDC cell is closely related to the high ionic conductivity of SNDC electrolyte. Moreover, the encouraging findings suggest that the SNDC can be as potential candidate in LT-SOFCs application.

Efficient Separation of Photoexcited Charge at Interface between Pure CeO2 and Y3+-Doped CeO2 with Heterogonous Doping Structure for Photocatalytic Overall Water Splitting

Enhancement of photoexcited charge separation in semiconductor photocatalysts is one of the important subjects to improve the efficiency of energy conversion for photocatalytic overall water splitting into H2 and O2. In this study, we report an efficient separation of photoexcited charge at the interface between non-doped pure CeO2 and Y3+-doped CeO2 phases on particle surfaces with heterogeneous doping structure. Neither non-doped pure CeO2 and homogeneously Y3+-doped CeO2 gave activities for photocatalytic H2 and O2 production under ultraviolet light irradiation, meaning that both single phases showed little activity. On the other hand, Y3+-heterogeneously doped CeO2 of which the surface was composed of non-doped pure CeO2, and Y3+-doped CeO2 phases exhibited remarkable photocatalytic activities, indicating that the interfacial heterostructure between non-doped pure CeO2 and Y3+-doped CeO2 phases plays an important role for the activation process. The role of the interface between two different phases for activated expression was investigated by selective photo-reduction and oxidation deposition techniques of metal ion, resulting that the interface between two phases become an efficient separation site of photoexcited charge. Electronic band structures of both phases were investigated by the spectroscopic method, and then a mechanism of charge separation is discussed.

Synthesis, Crystallography, Microstructure, Crystal Defects, Optical and Optoelectronic Properties of ZnO:CeO2 Mixed Oxide Thin Films

We report the synthesis and characterization of pure ZnO, pure CeO2, and ZnO:CeO2 mixed oxide thin films dip-coated on glass substrates using a sol-gel technique. The structural properties of as-prepared thin film are investigated using the XRD technique. In particular, pure ZnO thin film is found to exhibit a hexagonal structure, while pure CeO2 thin film is found to exhibit a fluorite cubic structure. The diffraction patterns also show the formation of mixed oxide materials containing well-dispersed phases of semi-crystalline nature from both constituent oxides. Furthermore, optical properties of thin films are investigated by performing UV–Vis spectrophotometer measurements. In the visible region, transmittance of all investigated thin films attains values as high as 85%. Moreover, refractive index of pure ZnO film was found to exhibit values ranging between 1.57 and 1.85 while for CeO2 thin film, it exhibits values ranging between 1.73 and 2.25 as the wavelength of incident light decreases from 700 nm to 400 nm. Remarkably, refractive index of ZnO:CeO2 mixed oxide-thin films are tuned by controlling the concentration of CeO2 properly. Mixed oxide-thin films of controllable refractive indices constitute an important class of smart functional materials. We have also investigated the optoelectronic and dispersion properties of ZnO:CeO2 mixed oxide-thin films by employing well-established classical models. The melodramatic boost of optical and optoelectronic properties of ZnO:CeO2 mixed oxide thin films establish a strong ground to modify these properties in a skillful manner enabling their use as key potential candidates for the fabrication of scaled optoelectronic devices and thin film transistors.

Synthesis and characterization of CeLaMO2 (M: Sm, Gd, Dy) compounds for solid ceramic electrolytes

In this study, pure CeO2 and Ce0.85La0.10M0.05O2 (M: Sm3+, Gd3+, Dy3+) solid electrolytes were synthesized using the sol-gel method and sintered at 1350?C for 12 h. X-ray diffraction (XRD) was used for crystal structure characterization of the ceramic solid electrolytes. After sintering, all prepared solid electrolytes were indexed to be cubic crystal lattices. The thermal properties of the prepared samples were investigated by thermogravimetric (TG) and differential thermal analysis (DTA) methods. The surface properties of the grain structure of the ceramic solid electrolytes were evaluated by scanning electron microscopy (FE-SEM) confirming the average grain size of about 1 ?m. The electrochemical impedance spectroscopy technique was used to investigate AC electrical properties of prepared solid electrolytes. The conductivity values at 750?C of the Ce0.85La0.10Sm0.05O2, Ce0.85La0.10Gd0.05O2 and Ce0.85La0.10Dy0.05O2 and pure CeO2 were found to be 1.10 ? 10?3 S/cm, 3.05 ? 10?4 S/cm, 8.85 ? 10?4 S/cm and 8.44 ? 10?10 S/cm, respectively. The characterization results showed that the La-Sm co-doped CeO2 sample can be used as a ceramic electrolyte in intermediate temperature solid oxide fuel cells (IT-SOFC).

On the Relative Stability of Near-Surface Oxygen Vacancies at the CeO2(111) Surface upon Zr Doping

Ceria (CeO2)-based materials are of great importance in numerous technological applications such as three-way catalysts (TWCs) [Catal. Today 62, 35-50 (2000) and Chem. Rev. 116, 5987-6041 (2016)], hydrocarbon reforming [Chem. Rev. 116, 5987-6041 (2016) and Catalysis by Ceria and Related Materials; Trovarelli, A.; Fornasiero, P., Eds.; 2nd Edition; Imperial College Press: London, 2013] and solid oxide fuel cells (SOFC) [Chem. Rev. 116, 5987-6041 (2016) and Catalysis by Ceria and Related Materials; Trovarelli, A.; Fornasiero, P., Eds.; 2nd Edition; Imperial College Press: London, 2013]. These materials possess a property that is key to most of such applications, namely, their capability for easy conversion between the Ce4+ and Ce3+ oxidation states, which is achieved by releasing oxygen atoms from the crystal lattice and forming oxygen vacancies. In particular, the replacement of Ce by Zr to form CeO2-ZrO2 solid solutions was found to facilitate the reducibility of the oxide as well as to increase the oxygen storage capacity and the system thermal stability, compared to pure CeO2. This theoretical work employing DFT+U calculations, is a systematic study of the effects of Zr doping on the stoichiometric and reduced CeO2(111) surfaces to determine the preferred location of the Zr dopants at various concentrations, as well as to pinpoint how Zr doping affects the stability of near-surface oxygen vacancies -including the position of the Ce3+ ions. We found that for a given Zr content, the more stable structures do not correspond to those configurations with Zr located in the topmost O-Ce-O trilayer (TL1), but in inner layers, and the stability decreases with increasing Zr concentration. Regarding the formation of oxygen vacancies, it was found that the most stable configuration corresponds to the Zr atom located in the surface layer (TL1) neighboring a subsurface oxygen vacancy with next-nearest neighbor Ce3+, being the formation energy equal to 1.16 eV. The corresponding surface oxygen vacancy is 0.16 eV less stable. These values are by 0.73 and 0.92 eV, respectively, smaller than the corresponding ones for the pure CeO2(111) surface. The results are explained in terms of Zr- and vacancy-induced lattice relaxation effects. This study provides microscopic insight into the interplay between Zr-doping, vacancy formation, lattice relaxations, and the localization of the excess charge that will be key to understanding surface chemistry and catalysis on Zr-doped ceria surface, as well as conductive ceria-based materials for advanced applications.<br>