CeO2 Layer Research Articles

Protective film on cerium metal through in-situ formation of a dense CeO2 oxide layer using air plasma

The rapid spontaneous oxidation of cerium in the atmospheric environment is reported to be attributed to its porous oxide structure, and there is a scarcity of strategies for enhancing its corrosion resistance. In this study, a dense ceria layer was fabricated in situ on the surface of cerium using a simple plasma process method, which significantly improved its resistance to drastic oxidation in air. By subjecting the cerium sample to plasma treatment in air for 400 s, a dense surface CeO2 layer with a thickness of approximately 1 μm was formed. Compared with untreated cerium metal samples, no significant changes were observed in terms of surface morphology and composition characteristics even after exposure to atmospheric conditions for up to 60 days. Theoretical calculations have demonstrated that the presence of a relatively stable CeO2 layer serves as an effective barrier against water adsorption/dissociation and particularly inward diffusion of hydrogen, thereby preventing their penetration into bulk cerium. The utilization of plasma method for generating a homogeneous surface oxide layer without introducing additional metal elements presents a novel strategy for protecting active metals exhibiting poor air corrosion resistance

Transformation of Arsenic from Poison into Active Site by Construction of Unique AsOx/CeO2 Interface for Stable NOx Removal.

Arsenic in the flue gas has been widely reported as a common poison for SCR catalysts; however, an appropriate coping strategy is still lacking to improve the arsenic resistance performance. Herein, a unique AsOx/CeO2 interface is constructed to transform arsenic from poison into active site with balanced acid-redox property, successfully achieving efficient NOx removal. The optimized AsOx/CeO2 exhibits high NOx removal efficiency, four times that of the As-poisoned V2O5/TiO2 catalyst, and even comparable to the state-of-the-art SCR catalysts. It was found that the As-O-Ce interfacial sites in oxygen-bridged As dimers on CeO2 can provide both Lewis acid sites and active lattice oxygen species, enhancing the adsorption and activation of NH3 to form key -NH2 intermediates, thereby facilitating the NH3-SCR reaction. More surprisingly, a thin CeO2 layer on the top of V2O5/TiO2 can capture arsenic to protect catalysts from arsenic attacking, which improves the catalytic activity to 2.8 × 10-7 mol g-1 s-1, even higher than that of fresh V2O5/TiO2 (2.0 × 10-7 mol g-1 s-1). Therefore, this strategy provides new ideas not only for designing antipoisoning SCR catalysts but also a feasible solution for the stable operation of commercial SCR catalysts in arsenic-containing flue gas.

Tribological Performance of Nano-CeO2/BNH2 Compound Lubricant Additive

To improve lubricant performance and extend the service life of machinery, the friction reduction and anti-wear performance of nano-cerium oxide (nano-CeO2) and nitrogen-containing heterocyclic borate (BNH2) composite additives were studied in this work, with the goal of obtaining better lubrication effects than a single additive. The results showed that the nano-CeO2 modified with Span80 had good dispersion stability in the base oil. The optimal addition mass fractions of single nano-CeO2 and BNH2 were 0.6 wt% and 1.0 wt%, respectively. Compared with the base oil, 0.6 wt% nano-CeO2 reduced the coefficient of friction by 44.9% and the wear spot diameter by 27.8%, while 1.0 wt% BNH2 reduced the coefficient of friction by 49.1% and the wear spot diameter by 32.8%. Compared with the single additions of nano-CeO2 and BNH2, the compound nano-CeO2/BNH2 further improved the friction reduction and anti-wear performance of the lubricating oil. Compared with the base oil, the 0.8 wt% nano-CeO2/1.0 wt% BNH2 composite additive reduced the coefficient of friction by 55.9% and the diameter of the abrasive spot by 48%. Physicochemical analysis of the wear surface revealed that the combination of nano-CeO2 and BNH2 had excellent synergistic effects. The generated lubricant films of nano-CeO2/BNH2 contained a chemical reactive layer of organic nitride (C–N), Fe2O3, FeO, and B2O3 and a physical adsorbent layer of CeO2 that provided great friction reduction and anti-wear effects during friction.

Investigating the Role of Grain Boundaries in Enhancing Bifunctional Memory Properties of CeO2 Thin Films

The rapid expansion of artificial intelligence (AI) has highlighted challenges for traditional von Neumann computing architectures, such as the memory and power limitations posed by complementary metal oxide semiconductor (CMOS) devices. Resistive random-access memory (RRAM) is considered to be an emerging technology for the next generation of non-volatile memory devices due to its simple metal/insulator/metal (MIM) structure, faster write/read speed, and longer retention time. CeO2 with defects is compatible with electrochemical metallization mechanisms make it ideal for use as an active material in memristors.We conducted the study with CeO2 thin film as the active layer. PVD-CeO2, containing numerous oxygen vacancies, facilitates gradual setting/resetting under low voltage conditions, which enables analog-type switching for applications such as artificial neural synapses. While, after annealing process, grain boundaries within the CeO2 layer serve as migration paths for rapid ion diffusion. When bias is applied to the Ag/CeO2/TiN memristor, electrochemical metallization (ECM) occurs within the CeO2 switching layer, leading to the migration of Ag ions and the formation of stable Ag conductive filaments in the CeO2 layer. Resistive switching allows the realization of typical RRAM devices with stable set/reset switching and an on/off ratio of up to 105. Overall, by varying annealing temperatures and operating voltages, the Ag/CeO2/TiN system can achieve bifunctional functionality. Figure 1

The Structure Dissection of Compacted CeO2/La2O3 Laminates by Spatially Offset Raman Spectroscopy

ABSTRACTTo tackle the challenge of non‐destructively analyzing complex oxide layers formed by atmospheric corrosion on active metals, we investigate the potential of inverse spatially offset Raman spectroscopy (inverse‐SORS) to detect corrosion products and elucidate how the spectroscopic features of SORS vary. This study explores the utilization of inverse‐SORS technology for longitudinal structural analysis of opaque CeO2/La2O3 laminates, which serve as a proxy for corrosion products. Through a combination of experimental measurements and Monte Carlo simulation, it demonstrates the feasibility of inverse‐SORS in non‐destructively elucidating the layered structure of these laminates. With increasing the spatial offset of this technology, the Raman intensity ratio of La2O3‐to‐CeO2 increases from 0.23 to 3.2 and then decreases to 0.27 for the CeO2/La2O3 sample with a 34‐μm‐thick CeO2 layer under 532‐nm excitation, whereas the bottom La2O3 layer is hardly detected when the thickness of the upper La2O3 layer increases to 225 μm. The results reveal that a thinner CeO2 layer facilitates the escape and detection of Raman signals originating from the bottom La2O3 layer, leading to an enhanced La2O3‐to‐CeO2 signal ratio and a reduced offset at the characteristic peak. The research also sheds light on the intricate interplay among multiple variables, such as spatial offset, laser wavelength, the corresponding absorption factor, the thickness of the oxide layer, and the compactness. These insights suggest that SORS is a valuable and non‐destructive approach for dissecting the structures of highly turbid composites of metallic compounds and semi‐quantitatively deducing their thickness.

Improvement in adhesion and corrosion resistance of Ce-based coating on micro-arc oxidized AZ31B Mg alloy via employing graphene oxide as an effective interlayer

Ce-based coatings are often used as protective coatings on Mg alloy because of their excellent self-healing and anticorrosion properties. However, poor adhesion of Ce coating can easily cause it peel off and thus lose its protective effect. In this work, for the first time, the graphene oxide (GO) was employed as an interlayer between micro-arc oxidation (MAO) and Ce-based coatings to improve their adhesion strength. The results show that the addition of GO layer can effectively improve the adhesion strength and hardness of the composite coating. The MAO/GO/Ce composite coating not only significantly enhance the corrosion resistance of the substrate, but also has self-healing ability. According to the molecular dynamics calculations, the GO interlayer can form a good bond with the inner MgO layer and the outer CeO2 layer. The MAO/GO/Ce composite coating with high adhesion and self-healing property may extend the practical application of Mg alloys.

Catalytic Ozonation of Pharmaceuticals Using CeO2-CeTiOx-Doped Crossflow Ultrafiltration Ceramic Membranes.

The removal of persistent organic micropollutants (OMPs) from secondary effluent in wastewater treatment plants is critical for meeting water reuse standards. Traditional treatment methods often fail to adequately degrade these contaminants. This study explored the efficacy of a hybrid ozonation membrane filtration (HOMF) process using CeO2 and CeTiOx-doped ceramic crossflow ultrafiltration ceramic membranes for the degradation of OMPs. Hollow ceramic membranes (CM) with a 300 kDa molecular weight cut-off (MWCO) were modified to serve as substrates for catalytic nanosized metal oxides in a crossflow and inside-out operational configuration. Three types of depositions were tested: a single layer of CeO2, a single layer of CeTiOx, and a combined layer of CeO2 + CeTiOx. These catalytic nanoparticles were distributed uniformly using a solution-based method supported by vacuum infiltration to ensure high-throughput deposition. The results demonstrated successful infiltration of the metal oxides, although the yield permeability and transmembrane flow varied, following this order: pristine > CeTiOx > CeO2 > CeO2 + CeTiOx. Four OMPs were examined: two easily degraded by ozone (carbamazepine and diclofenac) and two recalcitrant (ibuprofen and pCBA). The highest OMP degradation was observed in demineralized water, particularly with the CeO2 + CeTiOx modification, suggesting O3 decomposition to hydroxyl radicals. The increased resistance in the modified membranes contributed to the adsorption phenomena. The degradation efficiency decreased in secondary effluent due to competition with the organic and inorganic load, highlighting the challenges in complex water matrices.

Tuning of interface quality of Al/CeO2/Si device by post-annealing of sol-gel grown high-k CeO2 layers

A comprehensive study has been done on the influence of post-deposition annealing temperature on high-k cerium oxide (CeO2) layer grown on n-type silicon (Si) substrate and its resultant interface states have been studied for Al/CeO2/Si metal-oxide-semiconductor (MOS) devices. The high-k CeO2 thin films were deposited by spin-coating and sintered at different annealing temperatures (Ta) in the range of 400–900 °C. The parameters such as fixed charge density (Qeff), dielectric constant (k) of the layers, flat-band voltage (VFB), interface defect density (Dit), etc., of the MOS device were evaluated from CV and I-V measurements. A minimum value of flat band shift (∼0.05 V) with lower Qeff (−4.81 × 1011 C/cm2) have been achieved for the Ta of 600 °C. The k and Dit were evaluated to be 22 and 1.29 × 1012 cm−2, respectively at the Ta of 600 °C. In addition, the CV measurements showed a very small hysteresis and very low frequency dispersion for the Ta of 600 °C sample. Energy distribution of defect states was evaluated and it was maximum towards the bottom of the conduction band. This shows that the 600 °C is the optimum annealing temperature, which results in high quality interface, and the electron affinity of the corresponding CeO2 layers was found to be 3.29 eV as evaluated from ultraviolet photoelectron spectroscopy (UPS). Further, a maximum value of minority carrier lifetime (147 μs) has been achieved for the samples annealed at Ta of 400 °C, indicating that the post-annealing temperature plays a significant role on the properties of CeO2 films deposited by sol-gel process. Thus, the present study demonstrates the possibility of sol-gel grown high k-CeO2 layers suitable for MOS like devices.

Inverted loading strategy regulates the Mn–OV–Ce sites for efficient fenton-like catalysis

Regulating interfacial active sites to improve peroxymonosulfate (PMS) activation efficiency is a hot topic in the heterogeneous catalysis field. In this study, we develop an inverted loading strategy to engineer asymmetric Mn–OV–Ce sites for PMS activation. Mn3O4@CeO2 prepared by loading CeO2 nanoparticles onto Mn3O4 nanorods exhibits the highest catalytic activity and stability, which is due to the formation of more oxygen vacancies (OV) at the Mn–OV–Ce sites, and the surface CeO2 layer effectively inhibits corrosion by preventing the loss of manganese ion active species into the solution. In situ characterizations and density functional theory (DFT) studies have revealed effective bimetallic redox cycles at asymmetric Mn–OV–Ce active sites, which promote surface charge transfer, enhance the adsorption reaction activity of active species toward pollutants, and favor PMS activation to generate (•OH, SO4•−, O2•− and 1O2) active species. This study provides a brand-new perspective for engineering the interfacial behavior of PMS activation.

Corrosion resistance of hybrid plasma electrolytic oxidation coatings on AZ31B magnesium alloy in simulated body fluid

This study examines the effects of a hydroxyapatite/anatase TiO2/CeO2 coating on the corrosion of AZ31B magnesium alloy in a simulated body fluid. Plasma electrolytic oxidation (PEO) is used to create the coating, and the surface properties are analysed using X-ray diffraction (XRD), atomic force microscopy (AFM) and field-emission scanning electron microscopy (FE-SEM). Contact angle measurements adapted to compare the uncoated substrate (144.74 ± 2.08°) with the coated substrates, which exhibit contact angles of (107.92 ± 2.16°), (95.88 ± 2.06°) and (66.05 ± 2.09°) for the respective coating durations. Increasing the thickness of the coating improves its corrosion resistance. Specifically, a 6-minute PEO coating significantly increases the thickness and provides better protection against corrosion for the AZ31B magnesium alloy. Cross-sectional scans of the coated samples revealed an increase in specimen thickness from 32.92 μm to77.17 μm. Potentiodynamic polarisation tests in a simulated body fluid reveal that the 6-minute coated sample shows the highest corrosion resistance, with the lowest corrosion current density (1.9037 × 10-06) compared to other coatings, indicating strong protection against corrosion. This research proposes a novel method to enhance the corrosion resistance of PEO coatings on magnesium alloys by depositing a thicker layer of hydroxyapatite, anatase TiO2 and CeO2. This approach results in a stronger and more effective protective system against corrosion.

Ab initio study of quantized conduction mechanism in trilayered heterostructure for scaled down memory device applications

Interface of the layered heterostructure revealing the quantized conductance phenomena which cannot be achieved with either semiconducting layer alone in absence of externally applied electric field has wide range of applications in electronic industry of RRAM devices. A comprehensive analysis of electronic properties of CeO2/Ta2O5/CeO2 trilayered heterostructure has been carried out using first principle calculation employing VASP to explore the state of art of RRAM including barrier height, barrier width, conducting filament width and shape. For better understanding of conduction mechanism involved in RS, the influence of crystalline and amorphous phase of Ta2O5 sandwiched between CeO2 layers is analyzed by potential energy lineups, DOS, isosurface and integrated charge density plots. Origin of quantized states formed near the Fermi level in DOS is provided physically by growth of charge conducting filaments in isosurface charge density plots, and charge redistribution from Bader charge analysis. Outcomes of this study confirmed that with more quantized charge, crystalline Ta2O5 is better for interfacial RRAM devices. Apart from previously available findings, results of this study will provide new route to the potential application of this layered material in electronics especially storage devices.

Achieving a balance of rapid Zn2+ desolvation and hydrogen evolution reaction inertia at the interface of the Zn anode.

It is difficult to achieve fast kinetics of Zn2+(H2O)6 desolvation as well as HER inertia at the same electrolyte/Zn interface during long-term cycling of Zn plating/stripping in aqueous Zn-ion batteries. Herein, an effective interface construction strategy with hydrophilic transition metal oxides was proposed to achieve that balance using a CeO2 layer coating. The hydrophilic CeO2 layer can bring a balance between improving the access to the anode surface for Zn2+(H2O)6 electrolyte ions, providing uniform Zn2+ nucleation sites and HER inertia. What's more, Zn corrosion can be significantly inhibited benefiting from this coating layer. The efficiency of aqueous Zn-ion batteries showed a great enhancement. Ultra-long plating/stripping stability up to 1600 h and excellent recovery (returning to 0.5 from 20 mA cm-2) for the symmetric CeO2@Zn system were observed. A full cell with the MnO2 cathode (CeO2@Zn//MnO2) with good reversibility and stability (∼600 cycles) was fabricated for practical application. Our work provides a fundamental understanding and an essential solution to deal with the balance between rapid desolvation and inhibition of the hydrogen evolution reaction, which is important for promoting the practical application of rechargeable Zn batteries.

Phase textures of metal-oxide nanocomposites self-orchestrated by atomic diffusions through precursor alloys.

Metal-oxide nanocomposites (MONs) are of pivotal importance as electrode materials, yet lack a guiding principle to tune their phase texture. Here we report that the phase texture of MONs can be tuned at the nanoscale by controlling the nanophase separation of precursor alloys. In situ transmission electron microscopy (in situ TEM) has demonstrated that a MON material of platinum (Pt) and cerium oxide (CeO2) is obtained through promoted nanophase separation of a Pt5Ce precursor alloy in an atmosphere containing oxygen (O2) and carbon monoxide (CO). The Pt-CeO2 MON material comprised an alternating stack of nanometre-thick layers of Pt and CeO2 in different phase textures ranging from lamellae to mazes, depending on the O2 fraction in the atmosphere. Mathematical simulations have demonstrated that the phase texture of MONs originates from a balance in the atomic diffusions across the alloy precursor, which is controllable by the O2 fraction, temperature, and composition of the precursor alloys.

Edge cracking behavior of Y2O3 films based on the stress intensity factor

Hastelloy C-276 alloy is the preferred substrate for YBa2Cu3O7-δ (YBCO) coated conductors prepared by Ion-beam-assisted deposition (IBAD) route, but its surface is too rough to meet application requirements. Y(CH3COO)3·4H2O precursor solution has a low flattening efficiency, and its film edges are prone to crack formations. In this paper, a model for the stress intensity factor was established to study the effect of the presence of cracks on film stress. The simulation results showed that increasing the coating thickness reduced the overall stress, but increased the stress concentration at the crack. The larger bottom layer defects also made it easier for cracks to be generated. Then, 10-m long Hastelloy C-276/Y2O3 strips were prepared by colloidal-solution deposition planarization (CSDP), with an average surface roughness Rq of 0.427 and only 10 coating layers. This improved the flattening efficiency by 40 %, and a CeO2 layer with a good biaxial texture was finally prepared.

Machine Learning Designed and Experimentally Confirmed Enhanced Reflectance in Aperiodic Multilayer Structures

AbstractMachine learning (ML) methods have gained widespread attention in optimizing nanostructures for target transport properties and discovering unexpected physics. Here, an ML method is developed to discover and experimentally confirm binary CeO2‐MgO aperiodic multilayers (AMLs) for thermal barrier coatings with significantly enhanced reflectance. The effect of varying AML design parameters like total thickness, average period, and randomness in layer thicknesses, on the spectral and total reflectance is demonstrated. Introducing aperiodicity in layer thicknesses is shown to lead to a broadband increase in spectral reflectance due to photon localization. Since the number of possible AML structures increases exponentially with total thickness, a Genetic Algorithm optimizer is developed to efficiently discover AMLs with enhanced reflectance, for total thicknesses of 5–50 µm. Surprisingly, all the optimized structures show an odd number of layers with a CeO2 layer at both ends, deviating from the traditional way of designing binary superlattices with paired layers. The optimized AML and a reference periodic superlattice of 5 µm thickness are fabricated by Pulsed Laser Deposition and characterized by optical reflectance measurements. The fabricated AML, despite considerable fabrication uncertainty, still enhances the reflectance to 48% from 40% of the reference superlattice, validating the effectiveness of our ML‐based optimization process.

Support effects on Ru-based catalysts for Fischer-Tropsch synthesis to olefins

The effects of supports (CeO2, ZrO2, MnO2, SiO2 and active carbon) on the structure and catalytic performance of Ru-based catalysts for Fischer-Tropsch synthesis to olefins (FTO) were investigated. It was found that the intrinsic characteristics of supports and the metal-support interaction (MSI) would greatly influence the catalytic performance. The catalytic activity followed the order: Ru/SiO2 > Ru/ZrO2 > Ru/MnO2 > Ru/AC > Ru/CeO2. As far as olefins selectivity was concerned, both Ru/SiO2 and Ru/MnO2 possessed high selectivity to olefins (>70%), while olefins selectivity for Ru/ZrO2 was the lowest (29.9%). Ru/SiO2 exhibited the appropriate Ru nanoparticles size (~ 5 nm) with highest activity due to the relatively low MSI between Ru and SiO2. Both Ru/AC and Ru/MnO2 presented low CO conversion with Ru nanoparticles size of 1–3 nm. Stronger olefins secondary hydrogenation capacity led to the significantly decreased olefins selectivity for Ru/AC and Ru/ZrO2. In addition, partial Ru species might be encapsulated by reducible CeO2 layer for Ru/CeO2 due to strong MSI effects, leading to the lowest activity.

Tri-phase photonic crystal emitter for thermophotovoltaic systems

Thermophotovoltaics (TPVs) are devices that convert thermal radiation into electricity using a low-bandgap photovoltaic (PV) cell. While the theoretical efficiency can approach the Carnot limit, designing a TPV selective emitter that is spectrally matched with the PV cell's bandgap and is stable at high temperatures is critical for achieving high-efficiency systems. Photonic crystal (PhC) emitters can provide excellent spectral control, but prior experimental designs lack the thermal stability required for high-performance TPVs. In this study, a tri-phase PhC emitter design is proposed and optimized. The tri-phase design introduces an additional material in one of the alternating layers of an existing 1D PhC emitter, potentially stabilizing it at high temperatures. BaZrO3 is introduced in the CeO2 layers of a CeO2/MgO PhC emitter. Stanford Stratified Structure Solver (S4) is used to model the emittance of multiple tri-phase PhC variations. The parameter for optimization is the spectral efficiency of the emitter. The structure with the highest spectral efficiency is only 0.02% less efficient than the original design. The structure with the lowest spectral efficiency is only 0.28% less efficient. Therefore, any tri-phase variation can be applied to existing PhC emitters without compromising on their spectral efficiency. Without the need for manufacturing specific parameters, the tri-phase PhC can be an inexpensive emitter for real world applications that may improve thermal stability without compromising on the spectral efficiency, making the practical applications of TPVs feasible.

Mesoporous and dual-shelled hollow CeO2@CoNC nanospheres as efficient and stable oxygen reduction reaction electrocatalysts

The electrocatalytic oxygen reduction reaction (ORR) is the key bottleneck of fuel cells and rechargeable metal-air batteries, and recently, metalnitrogen complex carbon (MNC) demonstrates great potential in these fields. However, the complex and easily degraded MNC structure often results in inferior activity and poor durability in electrolysis. Herein, we fabricate a catalyst of h-CeO2@CoNC through the extended Stöber method and subsequent pyrolysis, involving the hollow CeO2 as the core and CoNC as the shell. The h-CeO2@CoNC catalyst exhibits notable ORR catalytic performances in 0.1 M KOH with a half-wave potential of 0.82 V and excellent durability, attributed to the synergistic interaction between CeO2 and CoNC matrix. Specifically, the inner layer of CeO2 is principally responsible for enhancing the chemical stability and the outer one of CoNC matrix is beneficial to boosting the ORR catalytic activity. This work provides an efficient preparation approach and further insight of rational design of the unique MNC catalysts for energy storage.

Defining optimal thickness for maximal self-field in YBCO/CeO2 multilayers grown on buffered metal

The effect of multilayering YBa2Cu3O (YBCO) thin films with sequentially deposited CeO2 layers between YBCO layers grown on buffered metallic template is investigated to optimize the self-field critical current density . We have obtained that the improvement in clearly depends on the YBCO layer thickness and temperature, where at high temperature can be increased even 50% when compared with the single layer YBCO films. Based on our experimental results and theoretical approach to the growth mechanism during multilayer deposition, we have defined a critical thickness for the YBCO layer, where the maximal self-field is strongly related to the competing issues between the uniform and nonuniform strain relaxation and the formation of dislocations and other defects during the film growth. Our results can be directly utilized in the future coated conductor technology, when maximizing the overall in-field by combining both the optimal crystalline quality and flux pinning properties typically in bilayer film structures.

Low-Temperature-Aged Synthesis of CeO2-Coated Li-Rich Oxide as Cathode for Low-Cost High-Energy Density Li-Ion Batteries

Co-free Li-rich oxide shows promise as a cathode for low-cost high-energy density Li-ion batteries but presents poor cyclic stability. To address this issue, a novel CeO2-coated Li-rich oxide composite is developed by applying a layer of CeO2 onto Co-free Li-rich oxide through a low-temperature-aged process. With this uniform coating, the resulting composite presents improved cyclic stability as well as rate capability as the cathode of a Li-ion battery. The capacity retention of the resulting composite is increased from 67% to 85% after 100 cycles, and its capacity retention of 5 C/0.05 C is enhanced from 10% to 23% compared with the uncoated sample. Such significant improvements indicate that this low-temperature-aged process is promising for preparing Co-free Li-rich oxides as cathodes of low-cost high-energy density Li-ion batteries.