Co-doped CeO2 Research Articles

Thermochemical reactivity of 5–15 mol% Fe, Co, Ni, Mn-doped cerium oxides in two-step water-splitting cycle for solar hydrogen production

The thermochemical two-step water-splitting cycle using transition element-doped cerium oxide (M–CeO2−δ; M=Fe, Co, Ni, Mn) powders was studied for hydrogen production from water. The oxygen/hydrogen productivity and repeatability of M–CeO2−δ materials with M doping contents in the 5–15mol% range were examined using a thermal reduction (TR) temperature of 1500°C and water decomposition (WD) temperatures in the 800–1150°C range. The temperature, steam partial pressure, and steam flow rate in the WD step had an impact on the hydrogen productivity and production rate. 5mol% Fe- and Co-doped CeO2−δ enhances hydrogen productivity by up to 25% on average compared to undoped CeO2, and shows stable repeatability of stoichiometric oxygen and hydrogen production for the cyclic thermochemical two-step water-splitting reaction. In addition, 5mol% Mn-doped CeO2−δ, 10 and 15mol% Fe- and Mn-doped CeO2−δ show near stoichiometric reactivities.

Structural, magnetic and optical properties of a dilute magnetic semiconductor based on Ce1−xCoxO2 thin film grown on LaAlO3

The enhancement of the room temperature ferromagnetism and optical properties of the dilute magnetic metal oxides is a crucial clue to construct spin-based optoelectronic devices. In this work, Ce1−xCoxO2 (0.01≤x≤0.15) thin films were prepared via ethylene glycol modified sol–gel spin coating technique on the LaAlO3 (001) substrate to enhance their room temperature ferromagnetism and optical properties. The structures, magnetic and optical properties of the prepared films were characterized by X-ray diffraction, atomic force microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, SQUID magnetometer, X-ray photoelectron spectroscopy and UV–vis spectrophotometer. The results demonstrated that a single phase cubic structure was formed, implying the substitution of Co ions into the Ce ions sites. The prepared films showed room temperature ferromagnetism with saturation magnetic moment of 1.09μB/Co was achieved for 5at.% Co-doped CeO2. This film exhibited high optical transparency of 85% and low optical band energy gap of 3.39eV. The improved magnetic and optical properties are argued to the increase of the density of the oxygen vacancies into the cerium oxide crystal structure due to the incorporation of Co ions.

Densification and grain growth behavior study of trivalent MO1.5 (M = Gd, Bi) doped ceria systems

Densification and microstructure for Ce0.9Gd0.1O1.95−δ and trivalent co-doped CeO2 (Ce0.9Gd0.06Bi0.04O1.95−δ) were investigated. The sinterability of co-doped nano-crystalline CeO2 was heightened compared to Gd-doped CeO2 according to the dilatometer measurements. The activation energy for densification was 745 and 419kJmol−1 for Gd-doped CeO2 and co-doped CeO2, respectively. The improved sintering behavior was attributed to the lower activation energy of co-doped CeO2. Investigations on the grain growth in the ceramics showed the suppressing effects of co-doped CeO2. The grain growth kinetics study indicated that the grain growth exponent, m, was 3 for Gd-doped CeO2, and 4 for co-doped CeO2, respectively.

Sr2+-Gd3+ co-doped CeO2: A cost-effective variant for IT-SOFC electrolytes

Cost effective Ce1−x−ySrxGdyO2−δ ceramics are developed and compared with Ce0.85Gd0.15O2−δ, in terms of their electrical properties. The amount of expensive Gd3+ is aimed to reduce by co-doping of low cost 2.5-5mol% Sr2+. Powder x-ray diffraction confirmed the single fluorite structure (space group Fm-3m) in all the prepared samples. The vital essence of the present study is that a slight Sr2+ co-doping allowed us to reduce a significant Gd3+ doping amount, with a gain in ionic conductivity, compared to Ce0.85Gd0.15O2−δ. For instance, Ce0.875Sr0.025Gd0.10O2−δ solid solution displayed the ionic conductivity, higher than Ce0.85Gd0.15O2−δ with 5mol% low Gd3+amount. The total electrical conductivities were found to be almost 1 000-10 000 times higher than electronic conductivity at air p(O2) i.e. 0.21bar, confirming the dominating ionic conduction. However, at extremely low p(O2), the samples show a mixed-ionic electronic conduction (MIEC) behaviour due to Ce4+ to Ce3+ reduction.

Densification Behavior and Space Charge Blocking Effect of Bi2O3 and Gd2O3 Co-doped CeO2 as Electrolyte for Solid Oxide Fuel Cells

Bi2O3 and Gd2O3 co-doped CeO2 is a promising electrolyte for its high electrical conductivity and low sintering temperature, but its densification behavior and the reason for the high conductivity are unclear. In this study, Ce0.9Gd0.1−xBixO1.95−δ (x=0−0.05) oxide has been synthesized by a co-precipitation method and its densification behavior and electrical conductivity are systematically investigated as the electrolyte material for solid oxide fuel cells. With the increase of Bi doping content, the sinterability of Ce0.9Gd0.1−xBixO1.95−δ is promoted. Based on the master sintering curve (MSC), the activation energy for densification process is calculated. Compared with Ce0.9Gd0.1O1.95 without Bi2O3 doping, the activation energy for the sample with Bi doping content x=0.04 is reduced from 725kJmol−1 to 450kJmol−1. The bulk conductivity increases gradually with Bi2O3 doping, which can be attributed to the increase of the free volume induced by Bi3+ with larger ionic radius than that of Gd3+. However, the grain boundary conductivity changes inconspicuously with different Bi doping content, which may be associated with the similar oxygen vacancy concentration in the space charge layer. For all the samples, the grain boundary conductivity is lower than the bulk conductivity at 300°C, which, according to the space charge blocking effect, can be attributed to the lower oxygen vacancy concentration in the space charge layers than that in the bulk.

One step synthesis and conductivity of alkaline and rare earth co-doped nanocrystalline CeO2 electrolytes

Gadolinia doped ceria (GDC) was co-doped with SrO (Sr–GDC), Pr2O3 (Pr–GDC) and doubly co-doped with SrO and Pr2O3 (Sr–Pr–GDC) and their effects on the electrical conductivity were studied. 20mol% gadolinia doped ceria and the co-doped compositions were processed in one step by solution combustion synthesis. X-ray diffraction (XRD) analysis confirmed the presence of a single cubic phase in the processed powders. The powders were found to be nanocrystalline in nature by transmission electron microscopy (TEM). A high relative density (≥94%) was obtained in the sintered pellets at lower sintering temperatures compared to microcrystalline ceria powders. SrO co-doping helped achieving a higher sintered density owing to low melting point of Sr. The relative density of GDC, Pr–GDC, Sr–GDC and Sr–Pr–GDC was 94.2%, 94%, 96.6% and 96.1% respectively. Ionic conductivity of the sintered pellets was measured using AC two-probe impedance spectroscopy. Both Sr and Pr co-doping resulted in considerable improvement in the conductivity of GDC. The doubly co-doped composition (Sr–Pr–GDC) exhibited higher conductivity compared to GDC, Pr–GDC and Sr–GDC.

Color tunability in green, red and infra-red upconversion emission in Tm3+/Yb3+/Ho3+ co-doped CeO2 with potential application for improvement of efficiency in solar cells

The preparation of Tm3+/Yb3+/Ho3+ co-doped CeO2 prepared by the precipitation method using ammonium hydroxide as a precursor is presented. By X-ray diffraction the materials show the phase-type of fluorite structure and the crystallite sizes were calculated by the Scherrer׳s equation. No other phase was observed evincing that the rare earth ions were inserted into the fluorite phase as substitutional or interstitial dopants. The microstrain calculated by the Williamson–Hall method do not show significant changes in their values, indicating that the inclusion of rare earths does not causes structural changes in the CeO2 used as a host matrix. All material showed intense upconversion emission at red and green region under excitation with diode laser at 980nm. The color of emission changes from green to red with increasing excitation power pump. The materials showed suitable photoluminescent properties for applications as a laser source, solar cells, and great emitter at 800nm.

Enhanced Room-Temperature Ferromagnetism on Co-Doped CeO2 Nanoparticles: Mechanism and Electronic and Optical Properties

The present study reports the effect of Co doping on the structural, optical, magnetic, and electronic properties of CeO2 nanoparticles (NPs) synthesized by a simple low-temperature co-precipitation method. Co doping was introduced by adding CoCl3 with different mole percentages (0%, 2%, 4%, and 6%) to cerium nitrate, which resulted in room-temperature ferromagnetism (RTFM). TEM and XRD analysis showed that the Co-doped CeO2 NPs are monodispersed with face centered cubic structure. The 6% Co-doped CeO2 NPs showed a coercivity value of 155 Oe and saturation magnetization of 0.028 emu/g at room temperature. The electronic structures of the as-prepared CeO2 and Co-doped CeO2 NPs were investigated by X-ray absorption near-edge structure (XANES) spectroscopy. The XANES spectra at Ce M- and L-edges clearly indicated a decrease in the valency state of Ce ions from Ce4+ to Ce3+ upon Co doping. This causes redistribution of oxygen ions and Co–Co bonding. The XANES study revealed that Co doping plays a prominent ro...

The effect of CO-doped on the room-temperature ferromagnetism of CeO2 nanorods

Abstract Co-doped CeO2 nanorods of 10–20 nm in diameter and 200–600 nm or more in length have been synthesized by a simple co-precipitation method. The results of XRD and SADE analysis indicate that the as-synthesized CeO2 samples have the fluorite structure. X-ray photoelectron spectroscopy and Raman spectra show that Ce4+ and Ce3+ ions coexist at the surface of non-doped CeO2 nanorods. The magnetic measurements indicated that Co-doped CeO2 nanorods exhibit stronger ferromagnetism at room temperature, and while increasing the amount of Co ions, the ferromagnetism increase more, which can be associated with the presence of Ce3+ and Co2+.

Cobalt-doped cerium oxide nanoparticles: Enhanced photocatalytic activity under UV and visible light irradiation

CeO2 nanoparticles (NPs) were synthesized by coprecipitation using cerium(III) nitrate hexahydrate as the precursor and ethanol as the solvent. Different concentration of cobalt-doped cerium oxide NPs (3mol % and 6mol %) were prepared by adding various concentrations of cobalt chloride to cerium nitrate. The as-synthesized NPs were characterized through X-ray diffraction (XRD) measurements, ultraviolet (UV)–visible spectroscopy, Photoluminescence (PL) spectroscopy, and transmission electron microscopy (TEM). XRD results reveal that the as-prepared CeO2 NPs had a face-centered cubic structure with crystallite size in the range of 5–8nm. TEM analyses showed that the CeO2 NPs and Co-doped CeO2 NPs had a homogenous size distribution (sizes were within 5–12nm). Band-edge absorption of CeO2 NPs redshifted upon increasing the Co concentration as compared to undoped CeO2 NPs. PL spectra reveal a peak shift of CeO2 emission upon cobalt doping, which were due to an increase in oxygen defects localized between the Ce4f and O2p energy levels (i.e., via formation of Ce3+ states). Photocatalytic degradation of methylene blue in aqueous solution under UV and visible (sunlight) irradiation in the presence of pure CeO2 NPs and of Co-doped CeO2 NPs was investigated. The efficiency of photocatalytic degradation of CeO2 NPs increased with the Co concentration both under UV irradiation and under visible light. Co-doped CeO2 NPs (6mol%) showed degradation efficiencies of 98% and 89% at 420min of exposure to UV irradiation and to visible light, respectively.

Surface treatment effects on CO oxidation reactions over Co, Cu, and Ni-doped and codoped CeO2 catalysts

We doped (M) and codoped (MM’) Co, Cu, and Ni into CeO2 support, and tested their gas-phase CO oxidation performance by temperature-programmed reaction mass spectrometry for the as-prepared, thermal H2- and N2-treated samples. Additionally, fundamental characteristics of doped CeO2 were revealed by transmission electron microscopy, optical microscopy, X-ray diffraction crystallography, UV–visible absorption, Brunauer–Emmett–Teller (BET) surface area measurements, and temperature-programmed reduction experiments. The CO oxidation performance was greatly improved upon metal-doping and thermal pre-treatment in H2 and N2 condition. It was found that Cu-contained samples showed higher CO performance while Ni, Co and CoNi-doped samples showed poor performances. The T10% (the temperature at 10% CO conversion) was lowered by 140 °C upon Cu-doping. Upon N2 (or H2-thermal treatment), the T10% was lowered by 80 and 110 °C for Cu-doped and undoped CeO2 catalyst, respectively. Overall, this study provides deeper information of surface treatment effects useful to development of efficient catalysts.

Optical and magneto-optical properties of Co-doped CeO2−δ films in the 0.5 to 4 eV range

Magnetically doped Ce1−xCoxO2−δ (nominal x = 0.05 and 0.10) films were systematically studied by spectroscopic ellipsometry and magneto-optical spectroscopy. The samples were prepared by pulsed laser deposition on MgO(100) substrates and grew as textured polycrystalline films with thickness between 200 and 750 nm. They exhibited room temperature ferromagnetism and an out-of-plane easy axis attributed to magnetoelastic effects from the in-plane compressive strain. The dispersion of dielectric function of Ce1−xCoxO2−δ films was parametrized by the sum of Tauc-Lorentz and damped Lorentz oscillators and adjusted numerically. Deduced optical band gaps were similar to those of pure CeO2, but the Co doping increased the optical absorption. The magneto-optical spectroscopy was carried out in both Faraday and Kerr configurations in the photon energy range from 0.5 to 4 eV, showing a strong dependence of the magneto-optical effect on the Co content near the optical band edge.

Solvothermal synthesis of nano-CeO<SUB align="right">2 and degradation of dye in indoor lighting

Azo dyes are an abundant class of synthetic, organic compounds containing one or more azo bonds (-N=N-). A large amount of these dyes are produced for using in different applications. However, their complex structure makes them difficult to biologically degrade. We sought to degrade acid orange 7 (AO7) using nitrogen-doped (N-doped) and carbon-nitrogen (C-N) co-doped nano-CeO 2 . N-doped monocrystalline CeO 2 nanoparticles was synthesised by solvothermal method using triethanolamine as a nitrogen source at 120°C for 24 h. C-N co-doped monocrystalline CeO 2 nanoparticles were synthesised by solvothermal method using hexamethylenetetramine as both nitrogen and carbon source at 140°C for 24 h. For purposes of comparison, a sample of undoped CeO 2 was synthesised using the dopant of neither triethanolamine nor hexamethylenetetramine. The doped and undoped CeO 2 monocrystals were all less than 10 nm in diameter. Nitrogen and carbon-nitrogen were shown to be incorporated into CeO 2 lattice from the results of both XRD and X-ray photoelectron spectroscopy analyses. The degradation of AO7 in water was investigated using a domestic 10 W compact fluorescent lamp. The results showed the degradation ratios of AO7 in the presence of nano-CeO 2 in the sequence of: C-N co-doped CeO 2 ≯ N-doped CeO 2 ≯≯ undoped CeO 2 , corresponding to magnitudes of 98.8%, 97.6%, and 48.2%, respectively.

Stochastic memristive nature in Co-doped CeO2 nanorod arrays

In this Letter, bipolar resistive switching characteristics of electrochemically deposited pure and Cobalt doped CeO2 nanorods architectures were reported. A conducting filament based model to address resistive switching process in these devices was proposed. Furthermore, the randomness in individual switching events and the prediction of switching probabilities were studied by imposing weak programming conditions. The present study offers insights into scrutinize the inherent stochastic nature in resistive switching characteristics within these devices rather than stressfully achieve high switching probabilities using excess voltage or time.

Intense up-conversion luminescence in Er3+/Yb3+ co-doped CeO2 powders

The Er3+ and Er3+/Yb3+ co-doped CeO2 powders have been prepared by a urea combustion route. The structural, morphological, compositional and vibrational analysis of the Er3+:CeO2 and Er3+/Yb3+:CeO2 powders have been studied by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray and Fourier transform infrared spectroscopy. The optical and luminescence properties of Er3+:CeO2 and Er3+/Yb3+:CeO2 powders have been studied by using laser excited spectroscopy. The effects of Yb3+ doping on up-conversion luminescence of Er3+ co-doped CeO2 powders were studied. The ratio of red to green intensity is decreased in Er3+:CeO2 whereas the ratio is increased in Er3+/Yb3+:CeO2 powders with increase of power. The effect of co-doping with the Yb3+ ions on the visible luminescence of Er3+ and the energy transfer mechanism responsible for the variation in the green and red intensity are discussed. The results indicate that these materials may be suitable for display and light emitting devices.

Upconversion luminescence properties of three-dimensional ordered macroporous CeO2: Er3+, Yb3+

• Three-dimensional ordered macroporous CeO 2 : Er 3+ , Yb 3+ was prepared. • UC emission in the 3DOM sample was obtained. • Relative intensity of the red to green emission increased in the 3DOM sample. Three-dimensional ordered macroporous (3DOM) Er 3+ , Yb 3+ co-doped CeO 2 and powder samples were prepared. The phase of the 3DOM sample was confirmed by XRD, and upconversion (UC) luminescence property was investigated. The results showed that green (527 nm, 548 nm) and red (659 nm) emission bands were observed in the 3DOM and powder samples under a 980 nm excitation at room temperature. It is interesting that the relative intensity of the red to green emission in the 3DOM sample increased in comparison with that of powder sample due to the increased non-radiative relaxation from 4 I 11/2 to 4 I 13/2 state in the 3DOM materials.

Magnetic characteristics of phase-separated CeO2:Co thin films

Herewith, we are reporting the magnetic properties of phase-separated Co-doped CeO2 films (with a Ce:Co atomic-ratio of 0.97:0.03) grown on single-crystal SrTiO3 (001) substrates. A comparison of the magnetic characteristics of these films with those of homogenously doped CeO2:Co films of the same composition illustrates the significant differences in their magnetic behavior. These behavioral characteristics provide a model for determining if the magnetic behavior observed in this, as well as in other diluted magnetic dielectric systems, is due to homogeneous doping, a mixture of doping and transition metal cluster formation, or exists purely as a result of transition metal clustering.

Infrared to visible upconversion luminescence in Er3+/Yb3+ co-doped CeO2 inverse opal

Infrared to visible upconversion luminescence has been investigated in Er3+/Yb3+ co-doped CeO2 inverse opal. Under the excitation of 980 nm diode lasers, visible emissions centered at 525, 547, 561, 660 and 680 nm are observed, which are assigned to the Er3+ transitions of 2H11/2 → 4I15/2 (525 nm), 4S3/2 → 4I15/2 (547, 561 nm), 4F9/2 → 4I15/2 (660 and 680 nm), respectively. The effect of photonic band gap on the upconversion luminescence intensity was also obtained. Additionally, the upconversion luminescence mechanism was studied. The dependence of Er3+ upconversion emission intensity on pump power reveals that it is a two-photon excitation process.

Electrodeposition of CeO2 and Co-Doped CeO2 Nanotubes by Cyclic Anodization in Porous Alumina Membranes

Electrodeposition of CeO2 and Co-Doped CeO2 Nanotubes by Cyclic Anodization in Porous Alumina Membranes

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.