Deposition Of CeO2 Research Articles

Preparation and characterization of cerium-doped multiwalled carbon nanotubes electrode for the electrochemical degradation of low-concentration ceftazidime in aqueous solutions

A modified multiwalled carbon nanotubes (MWCNTs) electrode doped with a rare earth metal, cerium, was prepared by electrodeposition. Scanning electron microscopy showed that cerium doping altered the microstructure and crystal orientation of the electrode surface, and the resulting electrode displayed a uniform and compact morphology. X-ray diffraction and X-ray photoelectron spectroscopy confirmed the successful deposition of CeO2 on the MWCNTs substrate. Cyclic voltammetry indicated that ceftazidime degradation on the modified MWCNTs electrode was irreversible. The Tafel curve showed that the modified electrode had a relatively high positive corrosion potential and a relatively low corrosion current density, indicating that the modified electrode could sustain a certain degree of corrosion. The degradation effects of the modified MWCNTs electrode on ceftazidime were evaluated systematically under different current densities, initial pH, supporting electrolyte concentration, electrode spacing, and initial ceftazidime concentration. The results suggested that the removal efficiency of ceftazidime with an initial concentration of 1mgL−1 was approximately 100% after 60min electrolysis in a 1gL−1 Na2SO4 supporting electrolyte solution with a current density of 3mAcm−2 and an electrode spacing of 1cm. The possible mechanism of ceftazidime degradation was monitored by liquid chromatography-mass spectrometry.

The use of CeO2-Co3O4oxides as a catalyst for the reduction of N2O emission

The morphological characterization of a series of cobalt-cerium oxide composites prepared by the deposition of CeO2 onto Co3 O4 powder with a molar ratio of cerium oxide to Co3O4 in the range of 0 to 1 was performed. The powders were also impregnated with a solution of K2 CO3 to obtain the theoretical content of potassium atoms 2at·nm−2 . To investigate the effect of adding specific amount of CeO2 on the catalytic activity, the X-ray diffraction, SEM-EDX, laser particle size distribution and BET surface area measurements were used. The catalysts were tested through the low-temperature decomposition of nitrous oxide in the temperature range of 50°C to 700°C. The addition of CeO2 and K always moved the temperature of a complete N2O conversion towards lower temperatures (480°C-540°C to 340°C-420°C). The best catalytic properties were shown by the samples in which the ratio of cerium oxide to cobalt oxide ranged from 0.4 to 0.7.

Mechanism of Self-Epitaxy in Buffer Layer for Coated Conductors

To elucidate the self-epitaxy mechanism of pulsed-laser deposition-CeO2, a hypothetical relationship with the substrate was derived based on the ion-beam-assisted deposition layer-processing method: the smaller the misorientation angle, the larger the crystallite size. In-plane misorientation angle dependences of crystallite sizes of ion-beam-assisted deposition-MgO and LaMnO3 as substrates for CeO2 deposition, obtained using X-ray diffraction and transmission electron microscopy, indicated that the hypothesis is plausible. This relationship is regarded as a prerequisite for self-epitaxy because large crystallites with small strains would be energetically favorable when CeO2 particles crystallize on them. Eventually, they will grow to dominant grains, which is a possible self-epitaxy mechanism.

Anodic Electro Deposition of CeO2 and Co-Doped CeO2 Thin Films

CeO2 and Co containing CeO2 thin films were deposited on indium tin oxide and stainless steel by anodic electrodeposition. Scanning electron microscopy showed that the films are flat and show globular morphology and cracks resulting from volume shrinking. According to XRD and Raman Spectroscopy pure ceria layers are crystalline, while the presence of Co induces the formation of amorphous films. The good adhesion and the compactness allowed the photoelectrochemical characterization of the films. A band gap value of 2.9 eV was estimated for CeO2, while slightly higher values (∼3.0 eV) were estimated for Co containing films. A mechanism for ceria anodic electrodeposition is proposed and discussed.

Lean NOx reduction on LNT-SCR dual-layer catalysts by H2 and CO

Lean reduction of NOx (NO & NO2) by H2 and CO was conducted over monolithic catalysts consisting of a selective catalytic reduction (SCR) catalyst layer deposited on top of a lean NOx trap (LNT) catalyst. An increase in the CO/H2 ratio decreased the cycle-averaged NOx conversion for the ceria-free LNT catalyst. CO poisoning was especially significant below 250°C. The low-temperature NOx reduction was increased either by use of an LNT-SCR dual-layer catalyst or deposition of CeO2 on the LNT catalyst. However, the ceria decreased the high-temperature reductive conversion of NOx due to promotion of the undesired NH3 oxidation. Ceria zoning enhanced the monolith NOx conversion. Downstream loading of ceria led to the highest NOx reduction at both low- and high- temperatures due to the beneficial interaction of the ceria and H2. The low-temperature NOx conversion of an aged dual-layer catalyst could be increased by a higher SCR catalyst loading. However, at high temperatures NOx reduction was independent of the SCR loading. The ratio of the lean to rich feed duration and the total cycle time were optimized to improve the NOx conversion in a temperature range from 150 to 400°C. The highest cycle-averaged NOx conversion was obtained with a 30s:5s lean-rich cycle containing 1.25% total reductant for all CO/H2 ratios for a lean feed containing 500ppm NO and 5% O2.

Nanostructured Spark Plasma Sintered Ce‐TZP Ceramics

In this work, spark plasma sintering (SPS) of 10 mol% CeO2‐doped ZrO2 nanocrystalline powders, obtained by a two‐step synthesis procedure, allows the preparation of fully densified nanostructured ceramics. The CeO2–ZrO2 powders with particle size below 100 nm are obtained after CeO2 deposition on hydrothermally synthesized ZrO2 particles by the impregnation method.Tetragonal CeO2–ZrO2 ceramics are obtained when sintering at 1200°C without holding time. A graded material containing tetragonal, monoclinic, and pyrochlore phases are obtained when sintering at 1200°C and for 5 min holding time. This is explained in terms of the gradual reduction of Ce4+ to Ce3+ species by carbon in the graphite environment during SPS. With the successful combination of the stabilizer coating technique and SPS, we achieve not only the stabilization of the tetragonal phase in the ceramics, but also good control of the grain size, by producing nanostructured ceramics with 40–70 nm grain sizes.

Preparation and Characterization of Nanocrystalline CeO2−Tb2O3 Films Obtained by Electrochemical Deposition Method

Nanocrystalline CeO2−Tb2O3 composite oxides films with various morphologies were prepared by electrodeposition under different conditions. These samples were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy (RS), and X-ray photoelectron spectroscopy (XPS). The magnetic properties of the samples were also studied. By increasing the concentration of Tb(NO3)3 or current density, the CeO2−Tb2O3 films with nanobelt structure changed into a blossom-shaped structure with lots of wrinkles and large surface area. XRD and Raman spectroscopy showed the crystal sizes of the samples to be 4−7 nm. XPS analysis indicated that higher current density was favorable to the deposition of CeO2 and inhibited the formation of Tb2O3. The morphology and magnetic property of the samples were determined by the composition. Only the sample mainly composed of Tb2O3 showed ferromagnetism.

Distribution of oxygen vacancies and gadolinium dopants in ZrO 2–CeO 2 multi-layer films grown on α-Al 2O 3

Gdolinia doped ZrO 2 and CeO 2 multi-layer films were deposited on α-Al 2O 3 (0001) using oxygen-plasma-assisted molecular-beam epitaxy. Oxygen vacancies and Gd dopant distributions were investigated in these multi-layer films using X-ray diffraction (XRD), conventional and high-resolution transmission electron microscopy (HRTEM), annular dark-field imaging in scanning transmission electron microscopy (STEM), X-ray energy dispersive spectroscopy (EDS) elemental mapping and X-ray photoelectron spectroscopy (XPS) depth profiling. EDS and XPS depth profiling reveal that the Gd concentration in the ZrO 2 layer is lower than that in the CeO 2 layer. As a result, a higher oxygen vacancy concentration exists in the CeO 2 layers compared to that in the ZrO 2 layers. In addition, Gd is found to segregate only at the interfaces formed during the deposition of CeO 2 layers on ZrO 2 layers. On the other hand, the interfaces formed during the deposition of ZrO 2 layers on CeO 2 layers did not show any Gd segregation. The Gd segregation behavior at every other interface is believed to be associated with the low solubility of Gd in ZrO 2.

Efforts for high throughput of IBAD-GZO-based substrate process for YBCO coated conductors

Efforts to improve a throughput of the IBAD-based biaxial substrate process are reported. IBAD-based biaxially textured substrates are now being typically fabricated at 1.2m/h for an IBAD-GZO layer and 6m/h for a CeO2 layer, respectively, in our laboratory. Since mass production is essential for commercialization, the production rate of IBAD process around 1m/h should be increased. In this work, we report a higher production rate of 1.5m/h with a 30m-piece sample by means of optimizing process conditions of multi-layered structure of IBAD and CeO2 layers. An in-plane alignment degree, Δϕ, of the substrate after CeO2 deposition obtained by X-ray ϕ-scan measurement was 4.6–5.8°. This level of texture can realize a high performance coated conductor with Ic×L=245A×212.6m as demonstrated by our group.

Multi-chamber deposition system for continuous production of YBCO coated conductors by thermal co-evaporation

We recently reported on a simple thermal co-evaporation route based on a reel-toreel system, that enables the production of 2 m-long superconducting tapes with Ic values up to 120 A/cm-width (Jc = 2 MA/cm2) and Tc = 88 K. This work describes the development of a new multi-chamber system designed for the continuous production of these tapes suitable for an industrial process. The system consists in three distinct vacuum chambers connected one with another by two specially designed 50 cm long slits. The length and cross-section of these slits have been calibrated in order to achieve a pressure difference up to 5 orders on magnitude across adjacent chamber. The system is originally conceived for the continuous production of CeO2 buffered RABiTS Ni-based tapes that require a pre-treatment of the bare metallic tapes in forming gas, followed by CeO2 deposition and a post-treatment in oxygen. To improve the robustness of the whole tape production process, we have designed and built a novel device based on a supersonic oxygen gas expansion for the continuous in situ oxygenation of YBCO during deposition. Here, we present preliminary results demonstrating the effectiveness of this device. Specifically, thanks to the enhancement of the number of collisions of the O2 molecules with the substrate due to the focused supersonic beam, we find that the oxygen pressure in the vicinity of the substrate can be up to 3 orders of magnitude higher than the background pressure in the chamber. The main advantage of this supersonic device is the insensitivity of the effective pressure to the substrate-nozzle distance, in the 2-5 mm range, which can be easily controlled during a continuous production process.

Catalytic steam reforming of ethanol over high surface area CeO2: The role of CeO2 as an internal pre-reforming catalyst

In the present work, it was found that high surface area ceria (CeO2 (HSA)), synthesized by a surfactant-assisted approach, have useful ethanol steam reforming activity under solid oxide fuel cells (SOFCs) temperatures. The catalyst provides good reforming reactivity and high resistance toward carbon deposition compared to Ni/Al2O3 and conventional low surface area ceria (CeO2 (LSA)). Although the hydrogen selectivity at steady state from the ethanol steam reforming over CeO2 (HSA) was lower than Rh/Al2O3, the resistance toward carbon deposition of CeO2 (HSA) was considerably higher.At temperature 900°C, the main products from the steam reforming of ethanol over CeO2 (HSA) (with inlet C2H5OH/H2O molar ratio of 1.0/3.0) were H2 (with the selectivity of 67.5%), CH4, CO, and CO2. In contrast, the formations of C2H4 and C2H6 were also observed from the steam reforming of ethanol over Ni/Al2O3 and CeO2 (LSA). The combination use of CeO2 and Ni/Al2O3 was studied in an annular ceramic reactor by applying CeO2 as an internal pre-reforming catalyst. The main purpose of CeO2 is to convert all ethanol and other high hydrocarbon compounds (e.g. C2H4 and C2H6) forming CH4, CO, CO2, and H2, while Ni/Al2O3 is applied to reform all CH4 left from the pre-reforming section and maximize the yield of hydrogen production. After operated at 900°C for 100h, this combination pattern offers high hydrogen selectivity (87.0–91.4%) and good resistance toward carbon deposition. This successful development eliminates the requirement of expensive noble metal catalysts or the installation of an external pre-reformer in order to reform ethanol internally (IIR-SOFC).

Processing Dependence of Texture, and Critical Properties of YBa2Cu3O7−δ Films on RABiTS Substrates by a Non‐Fluorine MOD Method

YBa2Cu3O7−δ (YBCO or Y123) films on rolling‐assisted biaxially textured substrates (RABiTS) were prepared via a fluorine‐free metallorganic deposition (MOD) through spin coating, burnout, and high temperature anneal. The effects of substrate texture and surface energy of the CeO2 cap layer were investigated. Except for the commonly accepted key factors, such as the textures of substrate and buffer layers, we found some other factors, for example, the deposition temperature of the cap layer, are also critical to the epitaxial growth of Y123 phase. With the CeO2 cap layer deposited at relative high temperature of 700°C, a critical current density, Jc, over 1 MA/cm2 has been demonstrated for the first time on Ni‐RABiTS by a fluorine‐free MOD method. Whereas for samples with CeO2 cap layers deposited at a lower temperature of 600°C, even though XRD data showed a better texture on these buffer layers, texture degradations of YBCO grains under the optimized processing conditions were observed and a lower oxygen partial pressure around 40 ppm was necessary for the epitaxial growth of Y123 phase. As a result, Jc fell to 0.45 MA/cm2 at 77 K. The observed phenomena points to the change of surface energy and reactivity of the CeO2 cap layer with respect to the CeO2 deposition temperature. In this paper, the YBCO phase diagram was also summarized.

Deposition of CeO2 Films on Si(100) Substrates by Electron Beam Evaporation

AbstractSummary: Thin films of cerium dioxide were deposited on silicon (100) substrates using e‐beam evaporation. The influence of different technological parameters, such as the substrate temperature, the oxygen pressure and the beam power on the crystallographic orientation of the films was explored. By optimizing these parameters, CeO2 thin films with a strongly preferred (200) orientation could be deposited on Si(100) substrates.XRD patterns of the CeO2 thin films deposited at various temperatures.imageXRD patterns of the CeO2 thin films deposited at various temperatures.

Hydrogen sorption properties for surface treated MgH 2 and Mg 2Ni alloys

In our group, strong enhancement of the hydrogen sorption capacities and kinetics of Mg and intermetallic alloys was recently achieved by surface treatments using physical and chemical means separately or in convert. In the latter, our approach consists in the preparation of tailor-made composites by ball-milling the alloy with preground graphite using specific milling conditions, followed by the deposition of Pd nanoparticles on the alloys surface using the polyol process. The benefit of graphite was ascribed to the carbon coating leading to the protection of the reactive metallic particles toward oxidation and the reduction character of carbon cleaning the alloy surface of NiO. Finally, the fine Pd particles deposited at the metallic surface probably act as hydrogen pumps during the desorption process. By combining both techniques, a hydrogen desorption as high as 3 wt.% in 60 min at 150 ° C and 6.2 wt.% in 30 min at 300 ° C are obtained for surface treated Mg 2Ni alloy and MgH 2, respectively. The latter treatment for MgH 2 is compared with the deposition of CeO 2 doped 6 at.% of Pt.

Electrochemical deposition of CeO2 on ZrO2 and Al2O3 thin films formed on stainless steel

Electrochemical deposition of CeO2 on ZrO2 and Al2O3 thin films formed on stainless steel

Deposition of CeO 2 and NiO buffer layers for YBCO coated conductors on biaxially textured Ni substrates by a MOCVD technique

CeO 2 and NiO buffers for YBCO coated conductors were deposited on biaxially textured Ni substrates by a metal-organic chemical vapor deposition method. The degree of texture and surface roughness of the oxide films were analyzed by X-ray pole figure, atomic force microscope (AFM) and scanning electron microscopy. The texture of deposited CeO 2 films was a function of deposition temperature and oxygen partial pressure ( P O 2 ). The (2 0 0) texture of CeO 2 was fully developed at T=500–520 °C and P O 2 =3.33 Torr. The growth rate of the CeO 2 films was 200 nm/min at T=520 °C and P O 2 =2.30 Torr, which is much faster than those prepared by other physical deposition methods. The (2 0 0) texture of NiO was formed at T=450 °C and P O 2 =1.67 Torr. The full width half maximum of the both films was in the range of 8–10°. The AFM surface roughness of the films was between 3.0–10 nm, depending on the deposition temperature.

Fabrication of SrRuO3 Epitaxial Thin Films on YBa2Cu3Ox / CeO2 / YSZ - Buffered Si Substrates by Pulsed Laser Deposition

ABSTRACTPseudocubic SrRuO3 (100) epitaxial thin films were fabricated on Si (100) with a YBa2Cu3Ox / CeO2 / YSZ (yttria-stabilized-zirconia) triple buffer layer ∼ 14 nm thick by pulsed laser deposition (PLD). Reflection high-energy electron diffraction (RHEED) and X-ray diffraction (XRD) revealed that the first buffer layer of YSZ (100) was epitaxially grown on naturally oxidized Si (100) substrates with the process condition of PB (base pressure) = 1×10-Torr, PO2 (oxygen partial pressure) = 5×10- Torr, and Ts (substrate temperature) = 700 °C. Higher deposition rate of YSZ in the range of 0 ∼ 0.6 nm/min brought about better crystallinity with a smaller value of a full-width at half maximum (FWHM) in the YSZ (200) rocking curve. Subsequent deposition of CeO2, YBa2Cu3Ox, and SrRuO3 resulted in an SrRuO3 (100) epitaxial thin film exhibiting good crystallinity with FWHM = 1.7° in the SrRuO3 (200) rocking curve.

Metal−Organic Chemical Vapor Deposition of CeO2 〈100〉 Oriented Films on No-Rolled Hastelloy C276

MOCVD has been applied to the first successful deposition of CeO2 〈100〉 oriented films on no-rolled Hastelloy C276. The presently found columnar grain morphologies have been related to the zone model proposed by Mochvan and Demchishin for physical vapor deposition processes. The fiber texture strongly depends on the deposition temperature.

Growth of Si Thin Films on CeO2/Si(111) Substrate Using Electron-Beam Evaporation

The growth mechanism of Si film on a CeO2(111)/Si(111) substrate has been investigated using X-ray diffraction (XRD), double crystal XRD (DCXRD), transmission electron microscopy (TEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). We have epitaxially grown a CeO2 film on the Si(111) surface by deposition of CeO2 at 640°C. When Si was deposited at 620°C on the CeO2(111)/Si(111) substrate using a high-vacuum e-beam evaporator, it was observed from XRD analysis that the Si film grew along the [111] direction. The TEM and AFM images showed that the top Si layer consists of large mountains and deep valleys. The XPS data showed no segregation of Ce on the Si layer surface. However, there was slight diffusion of Ce along the top layer Si grain boundary. These analysis results reveal that at the early stage of deposition, Si crystal nuclei are formed on a domain of the CeO2 film on Si(111) and grow three-dimensionally along the [111] direction, and eventually these merge into large mountains.

Homo-epitaxial deposition of CeO2 film by chemical vapour depositionon a CeO2/Ni substrate prepared by electron beam evaporation

Crack-free CeO2 films have been grown by chemical vapourdeposition (CVD) on a Ni substrate where a thin CeO2 film was pre-depositedby electron beam (e-beam) evaporation. Homo-epitaxial growth of CeO2 filmby CVD led to the development of a sharp cube texture inherited from a CeO2film pre-deposited by e-beam evaporation. The CeO2 film grown by CVD wasdeposited at 470 °C for 10 min and the film growth rate was measuredas 40 nm min-1. The extra XRD peaks having a relationship with a cubeorientation of 25-28° rotation around the ⟨001⟩ axis,i.e. the surface normal of the Ni substrate, were developed at the Ni/CeO2interface during film deposition. The present results show that thecombination of CVD and e-beam evaporation is useful for the fast deposition ofCeO2 film with a sharp cube texture.