Ceria Nanocubes Research Articles

Shape tailored nano-ceria as high performance supercapacitor electrode material

Electrochemical energy storage devices herald a brighter future, offering efficient and sustainable solutions to meet the escalating global energy demands. The current work investigates the development and characterization of different ceria nanostructures (nanorod, nanocube, and nanopolyhedra) as effective electrode materials for supercapacitor applications. The electrode materials are systematically characterized using various spectroscopic and non-spectroscopic techniques. Galvanostatic charge-discharge, electrochemical impedance spectroscopy, and cyclic voltammetry techniques are used to evaluate the electrochemical performance of the electrode materials. The optimum material for the said application is cerium nanorod which has the maximum specific capacitance of 437.27 F/g in acid electrolytes. The current-voltage (I-V) characteristics of the ceria nanostructures exhibit hysteresis behavior; ceria nanorod showing coexistence of memristive and memcapacitive nature. The loop area of the hysteresis curve, derived from the ratio of OFF resistance to ON resistance (ROFF/RON) at 4 V, yields approximate values of 1.08, 1.33, and 1.57 for ceria nanocubes, ceria nanopolyhedra, and ceria nanorods, respectively. Impedance vs. frequency analysis of the samples was also carried out to study their electrical and transport properties. The results obtained from electrochemical analyses are complimented by electrical studies.

Probing the structure of divalent impurity cations doped ceria nanocubes for photocatalytic activity

Ceria has attracted a lot of interest in scientific community due to its several technological uses. During this study, composite hydroxide-mediated method was used to prepare nanocubes of undoped and doped ceria. The prepared materials were characterized using a number of analytical techniques including room temperature powder X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) theory, and UV–Visible spectroscopy to investigate the structural, morphological, optical and photocatalytic properties. No impurity phases were observed from the XRD revealing face centred cubic (FCC) crystal symmetry of the undoped and doped ceria. The formation of nanocubes was confirmed by SEM. Pore sizes in the range of 24.9–29 mm were revealed by BET analysis. A gradual increase in photodegradation efficiency with an increase in irradiation time was seen for the doped samples compared to undoped ceria, showing suitability for photocatalytic applications. An increase in defect concentrations especially for Sr2+ doped samples indicated by the quantitative analysis of Raman spectra reveals potential for electrolytic applications in fuel cells provided necessary conductivity and long-term performance testing would need to be done.

Evolution of Ce4+ Lewis acidity during dehydroxylation of ceria nanoparticles with different morphology: An integrated FTIR, DFT and HRTEM study

Ceria is an important redox catalyst and its activity depends on the open Ce4+/Ce3+ sites, anion vacancies, surface OH groups and the ratio between them. We investigated the effect of dehydroxylation on the evolution of Ce4+ Lewis acidity of oxidized ceria nanocubes, nanopolyhedra, and nanorods. The {111} face is not hydroxylated and the exposed Ce4+ sites, after dehydration, adsorb CO weakly, forming linear carbonyls. The hydroxyl coverage of the {110} face consists of terminal and bridging hydroxyls, and dehydroxylation occurs between 423 and to 573 K by interaction between these groups. The produced Ce4+ sites form stronger linear carbonyls. The {100} face is covered by bridging OH groups, which are progressively removed even at 773 K. The created Ce4+ sites coordinate CO in a bridging mode and, at higher coverage, connect two bridging CO molecules. Ce4+ sites on edges and defects appear at high evacuation temperature and form mono- and dicarbonyls.

Interaction of O2 with Reduced Ceria Nanoparticles at 100–400 K: Fast Oxidation of Ce3+ Ions and Dissolved H2

The interaction between O2 and reduced ceria nanocubes was mainly investigated using FTIR spectroscopy. Nanorods and nanoparticles were also studied for comparison. Adsorption of O2 at 100 K on unreduced ceria produces only O2 molecularly adsorbed on Ce4+ sites. The Ce3+ cations on ceria reduced by H2 at 773 K were monitored using the 2F5/2 → 2F7/2 electronic transition band at 2133–2095 cm−1. This band possesses a fine structure well resolved at 100 K. The positions of the individual components depend on the Ce3+ environment, including the presence of nearby species such as OH groups. Even at 100 K, adsorption of O2 on reduced ceria leads to fast oxidation of about half of the Ce3+ cations, including all Ce3+ sites bound to OH groups and carbonates, and the simultaneous formation of superoxo (O2−) and peroxo (O22−) species. The remaining Ce3+ sites disappear upon heating up to 348 K. At higher temperatures, the peroxo species decompose directly, yielding lattice oxygen. Superoxides are converted to hydroperoxides, which then decompose into terminal OH groups. Reduced samples evacuated at T < 773 K contain sorbed H2. Part of this hydrogen is also fast oxidized even at 100 K.

Using Ex Situ and In Situ HERFD-XANES to Reveal the Superior Oxidation and Reduction Cycling of Ceria Nanocubes Dispersed in Silica Aerogel.

The oxygen storage capacity of ceria-based catalytic materials is influenced by their size, morphology, and surface structure, which can be tuned using surfactant-mediated synthesis. In particular, the cuboidal morphology exposes the most reactive surfaces; however, when the capping agent is removed, the nanocubes can agglomerate and limit the available reactive surface. Here, we study ceria nanocubes, lanthanum-doped ceria nanocubes, and ceria nanocubes embedded inside a highly porous silica aerogel by high-energy resolution fluorescence detection-X-ray absorption near edge spectroscopy at the Ce L3 edge. In situ measurements showed an increased reversibility of redox cycles in ceria nanocubes when embedded in the aerogel, demonstrating enhanced reactivity due to the retention of reactive surfaces. These aerogel nanocomposites show greater improvement in the redox capacity and increased thermal stability of this catalytic material compared to the surfactant-capped nanocubes. Ex situ measurements were also performed to study the effect of lanthanum doping on the cerium oxidation state in the nanocubes, indicating a higher proportion of Ce4+ compared to that of the undoped ceria nanocubes.

Spectroscopic Observation and Modeling of Photonic Modes in CeO2 Nanostructures.

Photonic modes in dielectric nanostructures, e.g., wide gap semiconductor like CeO2 (ceria), have the potential for various applications such as information transmission and sensing technology. To fully understand the properties of such phenomenon at the nanoscale, electron energy-loss spectroscopy (EELS) in a scanning transmission electron microscope was employed to detect and explore photonic modes in well-defined ceria nanocubes. To facilitate the interpretation of the observations, EELS simulations were performed with finite-element methods. The simulations allow the electric and magnetic field distributions associated with different modes to be determined. A simple analytical eigenfunction model was also used to estimate the energy of the photonic modes. In addition, by comparing various spectra taken at different location relative to the cube, the effect of the surrounding environment on the modes could be sensed. This work gives a high-resolution description of the photonic modes' properties in nanostructures, while demonstrating the advantage of EELS in characterizing optical phenomena locally.

Aging mechanisms of nanoceria and pathways for preserving optimum morphology

Thermal aging can modify the unique properties of a nanomaterial via structural change. Mechanistic understanding of the aging process, including accelerated aging under high-temperature operating conditions, is a first step towards property preservation via controlling, limiting, or suppressing aging-related processes. Here, we use molecular dynamics to simulate thermal aging of ceria nanocubes and nanorods, which transform into nanopolyhedra; comparisons with experimental TEM images are presented alongside. We find that morphology changes proceed via the turbulent mobility of CexOy surface clusters from one part of the nanoceria to another. For nanorods and nanocubes, catalytically important {100} and {110} surfaces are eroded, whereas the relative area of {111} surfaces increase. Detailed analysis of the simulations reveals that atoms in the CexOy clusters do not all move simultaneously. Rather, (-O-Ce-O-Ce-O-)n ‘chains’ (subsets of the larger CexOy clusters) move with collective motion, while the atoms inside the chains move in a ‘worm-like’ fashion. This reduces the activation energy barrier associated with all the atoms in the chain simultaneously moving into an activated (saddle point) configuration. We predict gadolinium-doped ceria nanocubes, charge-compensated by oxygen vacancies, age faster than undoped and fully oxidised ceria nanocubes. In particular, dopants that increase catalytic activity, may also accelerate aging by introducing oxygen vacancies that break the (-O-Ce-O-Ce-O-)n chains into smaller chains with reduced activation energies. Accordingly, we advocate that when doping is used to confer catalytic activity, experiment should also target the collective motion of surface (-O-Ce-O-Ce-O-)n chains to maximise thermal stability.

Plastic deformations of ceria nanocubes under compression: An atomistic simulations study

The mechanical properties and elementary deformation processes of ceria nanoparticles are investigated under uniaxial compression using quasi-static atomistic simulations and a fixed charge empirical potential. Results show a strong size-dependence of both the stress response and the plastic deformation phenomena that are characterized by amorphization and recrystallization processes that initiate from the surfaces in smaller-size samples, while the propagation of {111} nanotwins is observed in larger nanoparticles. In particular, we point out that the recrystallized phase is made of reoriented fluorite that behaves as a structural seed for the nucleation of 16<112>{111} partial dislocations at the origin of the nanotwins. Similarities with plastic deformation processes of FCC metals at the nanoscale are outlined and discussed.

Synergistic effect of acid-base and redox properties of nano Au/CeO2-cube on selective hydrogenation of nitrobenzene to aniline

Catalysts with 1 wt% gold doped on various morphologies of ceria (nano-cubes, nano-rods and nano-polyhedra), were prepared by the deposition precipitation method. The samples are characterized and used to catalyze the hydrogenation of nitrobenzene in ethanol. The highest nitrobenzene conversion (92%) and aniline selectivity (90%) are achieved from the catalyst supported by nano-cube CeO2 (1 wt% Au/CeO2-cube). The calcination temperatures of both the support and catalyst can influence the acid-base properties, the morphology and the valance of Au and Ce, which are key factors in the adsorption of nitrobenzene, the desorption of aniline and the formation of active H− species, respectively. We find that small-size Au nanoparticles (2.1 nm) with appropriate ratio of Au0 to Auδ+, acid/base sites with sufficient density and appropriate strength, and oxygen vacancy of ceria on the interface of Au and ceria are favorable to the formation of aniline on 1 wt% Au/CeO2-cube.

Combining Deep Learning and Compressed Sensing Methods for the 3D Characterization of Ultra‐Thin Epitaxial Layers Grown on Controlled‐Shape Nano‐Oxides

Using a nanostructured platform (a controlled‐shape nano‐oxide) and conventional wet impregnation techniques, powder‐type materials have been prepared in which atomically thin surface layers are deposited under very mild conditions. More importantly, an advanced methodology, combining energy dispersive X‐ray spectroscopy‐scanning transmission electron tomography (STEM‐EDX ET) and deep learning denoising techniques, has been developed for the 3D compositional characterization of these unique nanosystems. The complex case of LaOx‐coated CeO2 nanocubes is illustrated. For these, aberration corrected 2D STEM‐EDX evidence that ceria nanocubes become covered with a 2–4 atom‐thick layer of a La, Ce‐mixed oxide with spatially varying composition. However, STEM‐EDX ET reveals that this layer distributes unevenly, patching most of the available nanocube surface. The large flexibility and spread availability of the involved synthetic techniques enables, using the tools here developed, a wide exploration of the wealth of questions and applications of these intriguing, atomically thin, surface oxide phases.

Revealing Photonic Properties with High Spatial Resolution: An EELS Study on Ceria Nanocubes

Revealing Photonic Properties with High Spatial Resolution: An EELS Study on Ceria Nanocubes

Chlorine-Decorated Ceria Nanocubes for Facilitating Low-Temperature Cyclohexane Oxidative Dehydrogenation: Unveiling the Decisive Role of Surface Species and Acid Properties

Chlorine-Decorated Ceria Nanocubes for Facilitating Low-Temperature Cyclohexane Oxidative Dehydrogenation: Unveiling the Decisive Role of Surface Species and Acid Properties

Investigations of the Effect of H2 in CO Oxidation over Ceria Catalysts

The preferential CO oxidation (so-called CO-PROX) is the selective CO oxidation amid H2-rich atmospheres, a process where ceria-based materials are consolidated catalysts. This article aims to disentangle the potential CO–H2 synergism under CO-PROX conditions on the low-index ceria surfaces (111), (110) and (100). Polycrystalline ceria, nanorods and ceria nanocubes were prepared to assess the physicochemical features of the targeted surfaces. Diffuse reflectance infrared Fourier-transformed spectroscopy (DRIFTS) shows that ceria surfaces are strongly carbonated even at room temperature by the effect of CO, with their depletion related to the CO oxidation onset. Conversely, formate species formed upon OH + CO interaction appear at temperatures around 60 °C and remain adsorbed regardless the reaction degree, indicating that these species do not take part in the CO oxidation. Density functional theory calculations (DFT) reveal that ceria facets exhibit high OH coverages all along the CO-PROX reaction, whilst CO is only chemisorbed on the (110) termination. A CO oxidation mechanism that explains the early formation of carbonates on ceria and the effect of the OH coverage in the overall catalytic cycle is proposed. In short, hydroxyl groups induce surface defects on ceria that increase the COx–catalyst interaction, revealed by the CO adsorption energies and the stabilization of intermediates and readsorbed products. In addition, high OH coverages are shown to facilitate the hydrogen transfer to form less stable HCOx products, which, in the case of the (110) and (100), is key to prevent surface poisoning. Altogether, this work sheds light on the yet unclear CO–H2 interactions on ceria surfaces during CO-PROX reaction, providing valuable insights to guide the design of more efficient reactors and catalysts for this process.

Enhanced Artificial Enzyme Activities on the Reconstructed Sawtoothlike Nanofacets of Pure and Pr-Doped Ceria Nanocubes.

In this work, a simple one-step thermal oxidation process was established to achieve a significant surface increase in {110} and {111} nanofacets on well-defined, pure and Pr-doped, ceria nanocubes. More importantly, without changing most of the bulk properties, this treatment leads to a remarkable boost of their enzymatic activities: from the oxidant (oxidase-like) to antioxidant (hydroxyl radical scavenging) as well as the paraoxon degradation (phosphatase-like) activities. Such performance improvement might be due to the thermally generated sawtoothlike {111} nanofacets and defects, which facilitate the oxygen mobility and the formation of oxygen vacancies on the surface. Finally, possible mechanisms of nanoceria as artificial enzymes have been proposed in this manuscript. Considering the potential application of ceria as artificial enzymes, this thermal treatment may enable the future design of highly efficient nanozymes without changing the bulk composition.

Tailoring CO2 adsorption and activation properties of ceria nanocubes by coating with nanometre-thick yttria layers

Ceria (CeO2) is a ubiquitous component in catalysts for environmental protection processes, especially those devoted to CO2 valorisation. Aimed at preparing ceria-based nanomaterials with enhanced CO2 adsorption and activation properties, both the surface acid-base and redox features of ceria nanocubes were modulated by a novel, simple, wet chemistry synthetic strategy consisting of their coating with yttria (Y2O3) layers of variable thickness in the nanometre scale. The as-synthesised samples were characterised with special attention to their surface basicity and reducibility. Characterisation results revealed that the surface doping with yttria not only improved both the reducibility at low temperature and CO2 adsorption capacity of ceria nanocubes, but also introduced a variety of basic sites with different strength. Finally, the careful control of the yttria layer thickness allowed to modulate these effects and thereby the ability of nanostructured ceria to adsorb and activate the CO2 molecule.

Shape Effects of Ceria Nanoparticles on the Water‒Gas Shift Performance of CuOx/CeO2 Catalysts

The copper–ceria (CuOx/CeO2) system has been extensively investigated in several catalytic processes, given its distinctive properties and considerable low cost compared to noble metal-based catalysts. The fine-tuning of key parameters, e.g., the particle size and shape of individual counterparts, can significantly affect the physicochemical properties and subsequently the catalytic performance of the binary oxide. To this end, the present work focuses on the morphology effects of ceria nanoparticles, i.e., nanopolyhedra (P), nanocubes (C), and nanorods (R), on the water–gas shift (WGS) performance of CuOx/CeO2 catalysts. Various characterization techniques were employed to unveil the effect of shape on the structural, redox and surface properties. According to the acquired results, the support morphology affects to a different extent the reducibility and mobility of oxygen species, following the trend: R &gt; P &gt; C. This consequently influences copper–ceria interactions and the stabilization of partially reduced copper species (Cu+) through the Cu2+/Cu+ and Ce4+/Ce3+ redox cycles. Regarding the WGS performance, bare ceria supports exhibit no activity, while the addition of copper to the different ceria nanostructures alters significantly this behaviour. The CuOx/CeO2 sample of rod-like morphology demonstrates the best catalytic activity and stability, approaching the thermodynamic equilibrium conversion at 350 °C. The greater abundance in loosely bound oxygen species, oxygen vacancies and highly dispersed Cu+ species can be mainly accounted for its superior catalytic performance.

New Insights into the Bulk and Surface Defect Structures of Ceria Nanocrystals from Neutron Scattering Study

Neutron diffraction and pair distribution function studies coupled with Raman spectroscopy have successfully unraveled the detailed oxygen defect structures of ceria nanocubes and nanorods. Two types of defect sites are revealed for the ceria nanocrystals: surface and bulk defects. It is proposed that the surface oxygen defects in both types of CeO2 nanocrystals are predominantly the partially reduced Ce3O5+x, with the bulk defect structures dominated by interstitial Frenkel-type oxygen vacancies. Ceria nanorods possess much higher concentration of surface oxygen defects relative to the nanocubes, albeit with only slightly higher concentration of bulk Frenkel-type oxygen vacancies. Upon annealing the nanorod sample at 600 °C under vacuum (∼10–4 to 10–5 mbar), a partially reduced ceria phase with long-range oxygen vacancy ordering (Ce3O5+x) has been observed experimentally for the first time. This intriguing observation that surface defect phases can take on ordered defect sublattices under certain conditions is of great value in understanding the temperature-dependent catalytic performance of ceria nanocrystals. Furthermore, a drastic decrease of the surface vacancies in the ceria nanocrystals is observed upon exposure to SO2, especially for the nanorods, a likely origin for the sulfur poisoning effect on ceria-based materials. This study suggests that tailoring surface morphology is a promising strategy to control defect properties of ceria nanomaterials. It also provides fundamental insights to stabilize surface oxygen defects in CeO2 nanocrystals to achieve high redox performance under corrosive environments such as under SO2/SOx exposure.

Non-enzymatic free bilirubin electrochemical sensor based on ceria nanocube

Free bilirubin level is a significant indicator for the diagnosis of jaundice related diseases. Herein, ceria nanocubes are synthesized as catalyst for the direct electrochemical sensor of free bilirubin. The sensor is fabricated by simply modifying screen-printed electrodes with ceria nanocubes and carbon blacks. Owing to the catalytical activity of ceria nanocubes and conductivity of carbon blacks, this sensor can detect free bilirubin with high sensitivity and selectivity in a short response time. Under the optimized condition, the current of DPV peak is proportional to the bilirubin concentration up to 100 μM, with a LOD of 0.1 μM in phosphate buffer and 1 μM in human serum sample. The non-enzymatic sensor also shows good reproducibility and stability at room temperature. Moreover, only 5 μL test sample is required, the small sample consumption may facilitate the blood collection procedure. The sensor could be a potential candidate device for the point of care testing on free bilirubin in clinic.

Thermally stable surfactant-free ceria nanocubes in silica aerogel

Surfactant-mediated chemical routes allow one to synthesize highly engineered shape- and size-controlled nanocrystals. However, the occurrence of capping agents on the surface of the nanocrystals is undesirable for selected applications. Here, a novel approach to the production of shape-controlled nanocrystals which exhibit high thermal stability is demonstrated. Ceria nanocubes obtained by surfactant-mediated synthesis are embedded inside a highly porous silica aerogel and thermally treated to remove the capping agent. Powder X-ray Diffraction and Scanning Transmission Electron Microscopy show the homogeneous dispersion of the nanocubes within the aerogel matrix. Remarkably, both the size and the shape of the ceria nanocubes are retained not only throughout the aerogel syntheses but also upon thermal treatments up to 900 °C, while avoiding their agglomeration. The reactivity of ceria is measured by in situ High-Energy Resolution Fluorescence Detected - X-ray Absorption Near Edge Spectroscopy at the Ce L3 edge, and shows the reversibility of redox cycles of ceria nanocubes when they are embedded in the aerogel. This demonstrates that the enhanced reactivity due to their prominent {100} crystal facets is preserved. In contrast, unsupported ceria nanocubes begin to agglomerate as soon as the capping agent decomposes, leading to a degradation of their reactivity already at 275 °C.

The Sintering of Au Nanoparticles on Flat {100}, {111} and Zigzagged {111}-Nanofacetted Structures of Ceria and Its Influence on Catalytic Activity in CO Oxidation and CO PROX

The thermal stability of Au nanoparticles on ceria support of various morphology (nanocubes, nanooctahedra, and {111}-nanofacetted nanocubes) in oxidizing and reducing atmospheres was investigated by electron microscopy. A beneficial effect of the reconstruction of edges of ceria nanocubes into zigzagged {111}-nanofacetted structures on the inhibition of sintering of Au nanoparticles was shown. The influence of different morphology of Au particles on various ceria supports on the reducibility and catalytic activity in CO oxidation, and CO PROX of Au/ceria catalysts was also investigated and discussed. It was shown, that ceria nanocubes with flat {110} terminated edges are more suitable as a support for Au nanoparticles, used to catalyze CO oxidation, than zigzagged {111}- nanofacetted structures.Graphic