Nanocrystalline CeO2 Research Articles

High Surface Proton Conductivity of Epitaxial CeO2- δ Thin Film below Medium Temperature Range

Fluorite-type oxide such as Yttria-stabilized zirconia (YSZ) or doped-CeO2- δ ceramics are good electrolyte candidates for solid oxide fuel cells (SOFC) due to their high oxygen ion conductivity in high temperature range above 700 ºC[1]. Furthermore, porous and nanocrystalline CeO2- δ exhibit proton conduction at the surface below 100 °C[2]. This surface proton conduction is believed to the Grotthuss mechanism caused by the adsorption of water molecules. Since protons are produced by adsorbed water molecules and conduct through the layer of adsorbed water, oxygen vacancies and lattice constant are important parameters to enhance proton conduction. If high surface proton conduction can realize in CeO2- δ thin film, this may be more suitable than porous or nanocrystalline materials for new electrochemical devices and smart fuel cells.Recently, our group reported that the higher ion conductivity depends on the lattice constant and grain size for YSZ and Sm-doped CeO2- δ thin films[3,4]. However, the effect of crystallinity on the ion conductivity is not clarified. In this study, we have prepared the CeO2- δ thin films on YSZ (002) substrates by RF magnetron sputtering and probed their surface proton conduction below 300 °C in terms of electrical conductivity and electronic structure.The CeO2- δ ceramics target was prepared by solid-state reaction method. The CeO2- δ thin films with thicknesses of ~20 and ~120 nm were prepared by RF magnetron sputtering by adjust the deposition time. The sputtering conditions is followed; The base pressure was kept at 5.0×10-8 Torr and the deposition pressure was kept at 3.5 mTorr to control the Ar flow rate of ~2.67 sccm. The RF power was fixed at 30 W. The crystal and electrical structure of CeO2- δ thin films were evaluated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (PES) and X-ray absorption spectroscopy (XAS). The electrical characteristics was evaluated by A.C. impedance method.The prepared CeO2- δ thin films on the YSZ substrates were due to the exhibited 200 and 400 peaks. Figure shows the Arrhenius plot of the conductivity of the as-deposited and wet-annealed CeO2- δ thin films, indicating thermally activated behavior in the medium temperature range but different behavior below 100 °C. The conducting carrier in the medium and room temperature range is considered to be oxide ion and proton, respectively. In this poster, we will show that the surface proton conduction of CeO2- δ thin film is closely related to the lattice distortion and oxygen vacancies concentration at the surface.

(Invited) Structure and Reactivity of Cobalt-Containing Nanocomposites for Electrocatalytic Oxygen Evolution in Acid Medium

Electrochemical water splitting involves two heterogeneous multi-step half-reactions, which are referred to as the cathodic hydrogen evolution reaction (HER) and the anodic oxygen evolution reaction (OER). It should be noted that the OER under acidic conditions has the following two advantages compared to the process in neutral and alkaline solutions. The kinetics of the OER in acidic media could be much faster due to the higher proton transfer rate between anode and cathode. The proton exchange membrane (PEM) is an acidic solid polymer electrolyte membrane characterized by good proton conductivity, excellent electrochemical durability, and high mechanical strength.Polynuclear iron(III) hexacyanoferrate(II), or Prussian blue, and its analogues possess unique open framework structures with the general chemical formula of AxMy[Fe-(CN)6]z·nH2O (where A = alkali metal cation, M = transition metal cation). The possibility to accommodate different transition metal cations within the coordination framework renders them with appealing electrochemical, ion-exchange, sensing, or photomagnetic properties, which have been the subject of intense research for decades. Despite their rigid structure, these mixed-metal coordination polymers are usually nonstoichiometric. This chemical variety makes them a versatile type of molecule-based materials. Prussian Blue type cobalt hexacyanoferrates seem to activate water molecules during photoelectrochemical oxidations. Here we report the water oxidation catalytic activity found in Prussian blue-type cobalt hexacyanoferrate modified electrodes both under conventional electrochermcal and photoelectrochemical conditions (using WO3 n-type semiconductor) in acid medium. It is noteworthy that some of the hybrid cobalt-ruthenium hexacyanoferrate compositions showed remarkable catalytic ability towards the oxygen evolution reaction in acid electrolyte. The enhanced catalytic activities of the as-synthesized electrodes should also be attributed to such features as high population of hydroxyl groups and high Broensted acidity (due to presence of Ru or W oxo sites) and related fast electron transfers coupled to unimpeded proton displacements. The possibility of metal-metal interactions between nanosized metals (Co and Ru or Co and W) cannot be excludedFor comparison, we also show that mixed-metal oxide nanocomposites combining the favorable catalytic properties of Co3O4 and CeO2, nanocomposites (with different phase distribution and Co3O4 loading) can modify the cobalt-oxo-species and enhance its intrinsic oxygen evolution reaction activity. Synthesis of Co3O4-modified CeO2, which was addressed through three different sol-gel based routes, each with 10.4 wt% Co3O4 loading, yielded three different nanocomposite morphologies: CeO2-supported Co3O4 layers, intermixed oxides, and homogeneously dispersed Co. It is reasonable to expect that the local bonding environment of Co3O4 can be modified after the introduction of nanocrystalline CeO2, which allows the CoIII species to be easily oxidized into catalytically active CoIV species, thus avoiding the undesirable surface reconstruction process. Here, ceria is likely to regulate the surface oxygen concentration, due to its oxygen buffer (storage/release) capacity, associated with the fast CeIV/CeIII redox transition. Our research addresses the problems related to the fabrication of efficient earth-abundant catalysts for oxygen evolution reaction, and it provides strategies for designing more active and stable catalytic systems.

New insights into the immobilisation of Ce(IV) in Portland cement: Properties, hydration, microstructure and occurrence status of Ce

The immobilisation mechanism of Pu(IV) by Portland cement-based material is not well understood. This study aims to reveal the immobilisation mechanism and occurrence status of Ce(IV) (chemical analogue of Pu(IV)) in Portland cement paste. The addition of Ce(NO3)4 first slightly retarded then accelerated the early-age hydration of Portland cement, thereby resulting in an increase of compressive strength by 29 %. The main contributor to immobilisation of Ce is Portland cement rather than zeolite. The hydration products were not altered by Ce(NO3)4 addition, whereas the hydration degree and mean chain length of C-(Al/Ce)-S-H increased. Over 99.99 % of Ce was immobilised by synthesised C-S-H. A analysis of the synthesised C-S-H confirmed the formation of C-Ce-S-H, where Ce tetrahedra took the bridging site of silicate chain of C-Ce-S-H. Nano-crystalline CeO2 grains were identified, which intermixed with C-Ce-S-H. Approximately 90 % of Ce were immobilised by C-Ce-S-H, and the rest exist as nano-crystalline CeO2 grains.

Effect of Surface Treatment of Nanocrystalline CeO2 on Its Dephosphorylation Activity and Adsorption of Inorganic Phosphates.

The surface of nanocrystalline cerium oxide (CeO2) was treated with various chemical agents by a simple postmodification method at 25 °C and atmospheric pressure. Hydrogen peroxide, ammonium persulfate, deionized water, ascorbic acid, and ortho-phosphoric acid were used in order to study and evaluate their effect on surface materials, such as surface area, crystallite size, number of surface hydroxyl groups, particle morphology, and Ce3+/Ce4+ ratio. Paraoxon-methyl (PO) decomposition and inorganic phosphate adsorption were used to evaluate the effect of surface treatment on catalytic and adsorption properties. CeO2 surface was studied by Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, and acid-base titration. While the treatment procedure affected the number of surface hydroxyl groups and the amount of bulk surface oxygen vacancies, only negligible changes were observed in the Ce3+/Ce4+ ratio. Interestingly, surface treatment affected the ability to decompose PO, but only a small effect on inorganic phosphate adsorption was observed, indicating the robustness of CeO2 for the latter. A mechanism for possible interaction of the used chemicals with the CeO2 surface was proposed.

In Situ TEM/STEM Investigation of Crystallization in Y3Al5O12:Ce at High Temperatures Inside a Transmission Electron Microscope.

Y3Al5O12:Ce (YAG:Ce) phosphors are extensively used in the field of white light-emitting diodes (LEDs) due to their efficient luminescent properties. To optimize the performance of YAG:Ce phosphors, a comprehensive understanding of their synthesis and structural evolution is essential. This paper presents a direct in situ transmission electron microscopy (TEM) /scanning TEM (STEM) investigation on the transformation process of a precursor comprising nanocrystalline CeO2 dispersed in an amorphous Y-Al oxide matrix into crystalline YAG:Ce particles. The study reveals that nanocrystalline CeO2 particles dissolve completely in the Y-Al oxide matrix at a temperature above 900 °C, while YAlO3 (YAP)-type crystalline particles with Al2O3 phase in grain boundaries are observed above 1000 °C. Finally, YAG:Ce-type crystalline particles are formed above 1180 °C. Atomic-resolution energy-dispersive X-ray spectroscopy (EDS) elemental mapping demonstrates that the doped cerium (Ce) atoms occupy the same atomic sites as yttrium (Y). Photoluminescence measurements validate the efficient luminescent properties of the obtained YAG:Ce phosphor.

Response of ZrC to swift heavy ion irradiation

Zirconium carbide (ZrC) is commonly used for energy sector research, as well as a surrogate for the proposed advanced nuclear fuel candidate uranium carbide. This study investigates structural modifications to nanocrystalline and microcrystalline ZrC resulting from dense electronic excitations induced by swift heavy ion exposure. Samples were irradiated with 946 MeV Au ions to various fluences up to 6 × 1013 ions cm−2 and characterized using synchrotron-based x-ray diffraction. The evolution of the unit-cell parameter and heterogeneous microstrain were evaluated as a function of fluence and compared with those of nanocrystalline and microcrystalline CeO2 (a surrogate for UO2 fuel) irradiated under identical conditions. Distinct differences were observed in the radiation responses of the carbide and oxide across both grain sizes. Most notably, microcrystalline ZrC exhibits swelling characterized by two distinct regimes, which does not result in saturation at the ion fluences achieved. This contrasts with CeO2, which exhibits the well-documented direct-impact defect accumulation mechanism, reaching a steady-state saturation of swelling at higher fluences. Nanocrystalline CeO2 undergoes more pronounced swelling compared with microcrystalline CeO2, in contrast to nanocrystalline ZrC, which exhibits only minimal unit-cell changes. These results demonstrate that swift heavy ion-induced structural changes can be quite different in carbides and oxides, which must be considered when extrapolating fission-fragment type damage in current fuels to advanced fuels.

In situ preparation and determination of CeO2 high-index surface atomic structures

Understanding the properties regarding the high-index surfaces of the oxide nanocrystals is of great importance, but it remains challenging to obtain atomic-level information due to the lack of efficient preparation methods for high-index surfaces. Herein, we presented a work to in situ prepare and determine the intrinsic atomic structures of nanocrystalline CeO2 high-index surfaces via in situ spherical aberration (Cs)-corrected scanning transmission electron microscopy (STEM). By utilizing a reshaping process driven by the Wulff reconstruction, high-index surfaces of CeO2 nanocrystals including {210} {311}, and {533} were successfully prepared. Combined STEM with the density functional theory calculations, these high-index surface structures were determined with atomic precision, and interestingly {533} exhibited a unique atomic pit feature with low-coordinated Ce atoms exposure and unique electrical properties. This work has revealed new information about CeO2 high-index surfaces through experiments, enhancing our understanding of these surfaces, and also providing a new route for preparing high-index surfaces.

Influence of Defect Engineering in Nanocrystalline CeO2 for Therapeutics of Reactive Oxygen Species-mediated Disorders.

Intracellular oxidative stress generation is a root cause of the dysfunctioning of mitochondria that is accountable for neurodegenerative disorders. In nano-CeO2, the intrinsic redox cycle (Ce3+ ⇔ Ce4+) confers them with a distinct oxygen buffering ability. Thus, increasing the Ce3+/Ce4+ ratio by preferentially engineering oxygen vacancies is expected to boost the antioxidant characteristics in CeO2 nanocrystals (NCs) and hold promise in nanotherapeutics of neurodegenerative disorders. Here, a pristine, economic, and scalable synthesis route with rapid nucleation-growth to yield monodispersed CeO2 NCs of 4 nm has been employed. The NCs demonstrated sustained colloidal stability (zeta potential ~ -30.3±7.2 mV). The survival rate (~96.1% for 0.1 mg/mL) of healthy L929 cells and cell apoptosis induced on the SH-SY5Y cells (~ 30.2% for 0.1 mg/mL) indicate nano-CeO2s' prospects in nanomedicine. The formulated sustainable synthesis strategy for the enrichment of defects in these NCs is anticipated to pave the way for nanocrystal-based-treatments in smart healthcare.Clinical Relevance-This investigation signifies the oxygen vacancy-dependent therapeutic efficacy of CeO2 NCs by ensuring ~96.1% survival rate of L929 cells while demonstrating cell apoptosis on SH-SY5Y cells (~ 30.2%) to establish newer insights on treatment of neurodegenerative disorders.

Highly homogeneous multicomponent mesoporous catalysts: Defective amorphous vs. nanocrystalline CeO2 structure towards CO-PROX reaction

Mesoporous multicomponent materials with uniform pore sizes and well-defined network geometries are viewed as highly attractive candidates in the catalysis field. However, their synthesis at a high homogeneity level is considered quite challenging. Herein, alumina based mixed oxides (Al/Ce/Cu or Fe) are produced through a facile evaporation-induced-self-assembly route and tested towards preferential oxidation of CO in H2-rich gas. The effect of several synthetic parameters is investigated, with citric acid addition identified as a key factor in view of obtaining high mesoscopic order and notable homogeneity, particularly at high dopant amounts. Following thermal aging at 900 °C, metal oxides distribution and nanoporous nature are well-preserved with a parallel nucleation of ceria nanoparticles into the semi-crystalline inorganic framework. CO-PROX assessment of the aged samples reveals a drastic enhancement in catalytic activity, especially for the ternary Cu–Ce–Al system, associated with material's structural reconstruction strongly affecting metal–support interaction.

Influence of surface chemical properties of nanocrystalline CeO2 on phosphate adsorption and methyl-paraoxon decomposition

Nanocrystalline cerium oxide (CeO2) was used as an effective catalytic and adsorption material for the safe removal of selected phosphorus compounds. Several CeO2 samples were prepared by a simple coprecipitation method with subsequent annealing at temperatures between 400–600 °C, and their sorption ability for inorganic phosphates was studied together with their ability to decompose the organophosphorus compound - paraoxon methyl (PO) - with the goal to find the relations between the sorption and catalytic activity of the prepared materials. It was found that a complex set of physical and chemical characteristics (surface area, crystallite size, pore volume/size, the number of surface hydroxyl groups) plays a crucial role in the governing of adsorption ability and catalytic activity. From the dependence of some characteristics (i.e., the number of surface hydroxyl groups, BET surface area, crystallite size) on the annealing temperature and their mutual correlations, the model describing the degradation of organophosphate compounds on the surface of cerium oxide was deduced.

Dark and UV-Enhanced Degradation of Dimethyl Methylphosphonate on Mesoporous CeO2 Aerogels

Our development of high surface-area mesoporous expressions of ceria (CeO2) is motivated by recent studies identifying CeO2 as one of the most reactive oxides for adsorbing and degrading toxic organophosphorus compounds, including chemical warfare simulants. We synthesize nanostructured CeO2 aerogels using a facile, scalable, and template-free sol–gel method to amplify the number of available and accessible surface sites for organophosphorus adsorption/degradation and then spectroscopically characterize the degradation of dimethyl methylphosphonate (DMMP) at the aerogel surface. The CeO2 aerogels retain high concentrations of surface-sited residual Cl from the chloride sol–gel precursors, which block DMMP binding sites and hinder the formation of surface hydroxyls (OH). We demonstrate that a simple alkaline soak removes surface-fouling Cl and creates a more OH-rich surface, thus unleashing the hydrolytic activity of the amplified CeO2 aerogel surfaces. Whereas the Cl-fouled CeO2 surface weakly and reversibly binds DMMP, the rinsed, OH-rich surface irreversibly binds DMMP and rapidly generates hydrolysis products. Exciting the CeO2 bandgap with UV light (390–400 nm) accelerates DMMP degradation and generates a higher proportion of mineralized POx products than the dark reaction. Our work marks the first-ever report of photodegradation of a chemical warfare simulant at CeO2 as well as the first report of mineralized POx formation at CeO2 at room temperature. The high surface-area CeO2 aerogels exhibit higher capacity than non-networked, nanoparticulate CeO2, thus highlighting the potential applicability of nanocrystalline CeO2 aerogels for protection against organophosphorus compounds.

Influence of synthesis methods (combustion and precipitation) on the formation of nanocrystalline CeO2, MgO, and NiO phase materials

Attempts were made to prepare CeO2, MgO, and NiO nanomaterials by combustion and precipitation methods using aniline as a fuel and KOH as a precipitating agent (with the aid of PEG as a surfactant). The formation of CeO2, Mg(OH)2, and NiO as combustion products, and CeO2, Mg(OH)2, and Ni(OH)2 as precipitated products were obtained in a single step. In a single-step process, both combustion and precipitation methods yield CeO2 materials with the significant differences in XRD structural features. The annealing (500 °C/4h) treatment enhances the nanocrystalline nature with the formation of pure MgO, NiO, and CeO2 phases. Variation in refined lattice parameters is noted for the present different materials. The color appearance of the as-prepared and annealed materials obtained by these methods is differentiated. The as-prepared Ni(OH)2 phase materials produced via precipitation with PEG and without PEG as surfactant show a quite major difference in the structural (a, c, and D values) and thermal (TG/DTA) features. The phase pure as-prepared combustion product of CeO2 materials shows a relatively minimum weight loss of 1.4%. A maximum weight loss of 33.9% was noted for the precipitated product of Mg(OH)2 phase materials reduced to 28.2% despite the formation of pure MgO phase materials upon annealing at 500 °C/4h at the end temperature, 1000 °C. The UV–Vis diffuse reflectance measurements exhibit a difference in the absorbance peak intensity and the Eg values calculated from the Tauc relation ranging from 1.65 to 5.42 eV for annealed MgO, NiO, and CeO2 phase materials. Significant changes in the NIR reflectance (<10 – 80%) values are seen in the 750–2500 nm regions for these nanomaterials owing to the difference in the color appearance of powder samples. From the NIR reflectance spectral study, we found that the MgO and CeO2 nanomaterials are suitable for NIR reflecting solar and color pigmentation applications owing to their higher (∼80%) NIR reflectance values in the NIR region.

Multicomponent one pot synthesis of Substituted 3,4-Dihydropyrimidin-2-(1H)-ones by Nanocrystalline CeO2

One of the most prominent multicomponent reactions (MCRs), Biginelli reaction has been utilized for the synthesis of 3,4-dihydropyrimidin-2-(1H)-ones catalyzed one-pot condensation of aldehyde, β- ketoester and urea in presence of ethanol. The present study deals with synthesis of biologically active 3, 4- dihydropyrimidin-2(1H)-ones using nano crystalline CeO2.

Effect of indium doping on the structural, optical and electrochemical behaviors of CeO2 nanocrystalline thin films

Undoped and indium (In) doped cerium oxide (CeO2) nanocrystals (NCs) have been successfully synthesized onto glass and glass coated indium-doped tin oxide (ITO) substrates under optimized conditions via spray pyrolysis at 450 °C, with simultaneous insertion of In at different percentages (0, 2, 4, 6, 8 at. %) as a dopant. Several techniques for characterization were utilized to investigate the indium effect on the microstructural, optical, morphological and electrochemical properties of the CeO2 material. The as-prepared samples show well-defined face centered cubic fluorite structure grown along [200]. Raman spectroscopy was used to investigate the imperfections where longitudinal optical mode confirmed the existence of imperfections in the form of oxygen vacancies. Peak asymmetry and width of Raman active mode are ascribed to the presence of Ce3+ ions and oxygen vacancies, which was affected by the insertion of In3+ ions in the CeO2 nanocrystals. Scanning electron microscopy (SEM) images showed that the morphologies of the samples was influenced by indium incorporation. The optical properties result via transmittance and absorbance analysis within the UV–Vis–NIR domain exhibited that the samples are highly transparent (78–83%). The obtained band gap energy (Eg) depends on the percentages of the In dopant. The results of cyclic voltammetry (CV) show that In addition helps to enhance the ion storage capacities (ISC) of CeO2 material. The CeO2 doped thin films remained completely transparent after the insertion/extraction of Li+ ions. These important results widen the field of application of this oxide, particularly for electrochromic devices.

Oxygen vacancies and defects tailored microstructural, optical and electrochemical properties of Gd doped CeO2 nanocrystalline thin films

In this study, the authors present a pure and Gadolinium (Gd) doped CeO2 nanostructures, successfully elaborated onto the glass and Indium Tin Oxide (ITO) coated glass substrates under optimized parameters. A spray pyrolysis method was used at a temperature of 450 °C, with simultaneous incorporation of Gd at various concentrations (0, 2, 4, 6, 8 at. %) as a dopant. Different techniques for characterization were used to study the Gd impact on the microstructural, the morphological, the optical and the electrochemical behaviors of the CeO2 material. The XRD patterns shows that Gd3+ ions are inserted at the Ce4+ ion sites in the cubic fluorite structure network of CeO2 nanocrystals (NCs). Raman spectroscopy and UV–Vis–NIR have been utilized to study the defect structure and optical behaviors in these NCs. Broadening and Peak asymmetry of Raman active mode are attributed to the existence of Ce3+ and oxygen vacancy, which have been changed with addition of Gd3+ ions in CeO2 NCs. The results of UV–Vis–NIR spectroscopy show the variations of the optical gap energy with fluencies of Gd3+ due to the variations of particles sizes of NCs. Cyclic voltammetry results show that the ion storage capacities (ISC) of CeO2 thin films are increased with Gd doping. This research paper reports on the fluencies of Gd doping in CeO2 nanocrystals, to understand the role of oxygen vacancies and the impact they have on the tailoring of the microstructural, optical and electrochemical behaviors of doped CeO2 nanocrystals for multiple applications such as, catalysts, oxygen transportation, ultraviolet fuel cells, and electrochromic devices etc.

Unravelling the synergistic effect on ionic transport and sintering temperature of nanocrystalline CeO2 tri-doped with Li Bi and Gd as dense electrolyte for solid oxide fuel cells

Microstructural and electrochemical investigations of tri-doped (Gd, Li and Bi) cerium oxide, with theoretical formula Ce0.8(1−x-y)Gd0.2(1−x-y)LixBiyO[1.9(1−x-y)+x/2+3y/2] (x = 0.02 or 0.03 and y = 0.03 or 0.02 and x + y = 0.05) were carried out by XRD, BET, SEM, Raman, and EIS analyses. According to the dilatometer analysis, the synergistic combination of lithium and bismuth promotes the reduction of sintering temperature down to 800–900 °C. A densification> 95% was achieved for the electrolytes sintered at 900 °C. Raman analysis, in agreement with XRD, demonstrated that the lithium and bismuth induced changes due to the growth of the topological disorder and a higher defectiveness provoked by doping. The high dopant concentration (5 mol%) is well distributed into the lattice and forms a complex network of defects that traps the oxygen vacancies and hence mobile ions promoting the ionic transport. As compared to a single (CGO) or a bi-doped system (BiCGO and LiCGO) an improvement of total conductivity was achieved at lower sintering temperature, with a maximum value for Ce0.76Gd0.19Li0.03Bi0.02O1.85 of 2.68·10−3-1.66·10−1 S cm−1 in temperature range of 400–800 °C.

A Facile Method of Synthesis and Characterization of Sr Doped CeO2 Nanocrystalline Materials

Strontium doped Cerium oxide (Ce1-0.25Sr0.25O2 and Ce1-0.5Sr0.5O2) nanocrystals were synthesized by combustion technique. The synthesized (Ce1-xSrxO2, x = 0.25, 0.5) nanocrystals were annealed at 500° C for 2hr. The phase formation, surface morphology and elemental composition analysis have been studied using XRD, HRSEM and EDXS. XRD and HRSEM measurements revealed that the synthesized nanocrystals were in single phase with face-centered cubic (fcc) structure and that the nano-grains had different sizes. Chemical composition was confirmed using EDXS. The UV-Vis spectroscopic studies revealed that as the Sr doping level increases, the band gap width increases from Eg = 2.9 eV to 2.95 eV. At the same time, the wavelength of maximum absorbance shifts from λabs = 285 to 300 nm. Further, PL studies were performed with excitation wavelength λ = 350 nm and two main emission peaks were observed at 415 and 437 nm respectively. TGA, DTA and DSC measurements were carried out to check the weight loss and the occurrence of endothermic/exothermic reactions

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.

High Pressure Brillouin Spectroscopy and X-ray Diffraction of Cerium Dioxide

Simultaneous high-pressure Brillouin spectroscopy and powder X-ray diffraction of cerium dioxide powders are presented at room temperature to a pressure of 45 GPa. Micro- and nanocrystalline powders are studied and the density, acoustic velocities and elastic moduli determined. In contrast to recent reports of anomalous compressibility and strength in nanocrystalline cerium dioxide, the acoustic velocities are found to be insensitive to grain size and enhanced strength is not observed in nanocrystalline CeO. Discrepancies in the bulk moduli derived from Brillouin and powder X-ray diffraction studies suggest that the properties of CeO are sensitive to the hydrostaticity of its environment. Our Brillouin data give the shear modulus, = 63 (3) GPa, and adiabatic bulk modulus, = 142 (9) GPa, which is considerably lower than the isothermal bulk modulus, 230 GPa, determined by high-pressure X-ray diffraction experiments.

Promotion effect of rare earth elements (Ce, Nd, Pr) on physicochemical properties of M-Al mixed oxides (M\u2009=\u2009Cu, Ni, Co) and their catalytic activity in N2O decomposition

A series of M-AlOx mixed oxides (M = Cu, Co, Ni) with the addition of high loadings of rare earth elements (REE, R = Ce, Nd, Pr; R0.5M0.8Al0.2, molar ratio) were investigated in N2O decomposition. The precursors were prepared by coprecipitation and subsequent calcination at 600 °C. The obtained mixed metal oxides were characterized by X-ray diffraction with Rietveld analysis, N2 sorption, and H2 temperature-programmed reduction. Depending on the nature of REE and the initial M-Al system, R cations could be separately segregated in oxide form or coordinated with the transition metal cations and form mixed structures. The addition of Ce3+ consistently led to nanocrystalline CeO2 mixed with the divalent oxides, whereas the addition of Nd3+ or Pr3+ resulted in the formation of their respective oxide phases as well as perovskites/Ruddlesden–Popper phases. The presence of REE modified the textural and redox properties of the calcined materials. The rare earth element-induced formation of low-temperature reducible MOx species that systematically improved the N2O decomposition on the modified catalysts compared to the pristine M-Al materials by the order of Co > Ni > Cu. The Ce0.5Co0.8Al0.2 catalyst revealed the highest activity and remained stable (approximately 90% of N2O conversion) for 50 h during time-on-stream in 1000 ppm N2O, 200 ppm NO, 20 000 ppm O2, 2500 ppm H2O/N2 balance at WHSV = 16 L g−1 h−1.