Ceria Films Research Articles

The effect of gadolinium-doped ceria interlayer on the oxygen reduction reaction in a LSCF cathode-ScSZ electrolyte supported IT-SOFCs

Solid oxide fuel cells (SOFCs) are rapidly emerging as a technology, offering the potential for carbon neutral or carbon negative generation of electricity and heat (combined heat and power) using synthetic carbohydrate fuels and hydrogen. A significant challenge associated with SOFCs is the high polarization resistance experienced at the cathode during the oxygen reduction reaction (ORR), which diminishes the cell efficiency. The kinetics of the ORR are influenced by factors such as the cathode material type, its microstructure, and the quality of the interface between the cathode and electrolyte. In our research, we have addressed this issue by modifying the interface between the state-of-the-art cathode material, Lanthanum Strontium Cobalt Ferrite—La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF), and the Scandia stabilized Zirconia (ScSZ) electrolyte. This modification involved the deposition of a micron-sized film of ion-conducting gadolinium-doped ceria (Gd0.1Ce0.9O2-δ) – (GDC) as an interface layer. Our analysis involved systematic studies, including variations in cell operating temperatures and applied potentials, as well as measurements of cell performance over an extended period. We observed a significant enhancement in cell performance with the introduction of the GDC interfacial layer between the LSCF cathode and ScSZ electrolyte. Specifically, we recorded a cathode polarization resistance as low as 0.40 Ωcm2 for the modified interface, which is substantially lower compared to bare LSCF cathodes (3.04 Ωcm2) at 600 °C. This reduction in cathode resistance can primarily be attributed to the improved conditions for the oxygen reduction reaction (ORR), resulting from enhanced interfacial contact between the electrode and the electrolyte and mitigation of any zirconium interdiffusion as seen from detailed scanning electron microscopic studies.

Hybridization-mediated quasiparticle and phonon dynamics in single crystal cerium films

Hybridization-mediated quasiparticle and phonon dynamics in single crystal cerium films

Characterization of Ceria Films in SBA-15

Characterization of Ceria Films in SBA-15

Proliferation in the photo-response characteristics of MDC thin films for optoelectronic applications through NSP technique

Nebulizer spray pyrolysis (NSP), a simple thin-film deposition method, was used to fabricate p-Si/n-manganese-doped cerium oxide (MDC)/Al photodiodes. The structure, morphology, optics, composition, electrical and rectifying properties of the prepared materials were analyzed. UV-Vis analysis demonstrates a prominent and acute absorption edge at 425 nm in the visible region. As more Mn impurities are incorporated into CeO2 crystallites, the band gap decreases as the doping level increases, leading to the formation of new recombination sites with low energy emissions. Electrons in outer orbits operate in energy bands, moving to higher energy levels. At higher Mn doping, some NBE emissions and green emission peaks disappear. The emission spectrum confirmed that strong and broad blue emission peak occurred for the diode containing the 15% Manganese Diode Cerium film. XRD peak shows the mono-phase polycrystalline cubic fluorite structure with the main orientation in the 200 directions. The broad lines (CeO) symmetry at 695,659,538 and 517 cm−1 observed in the Fourier Transform -Infrared spectrum are due to the phonons of the cerium oxide (Ce-O) network caused by asymmetric tip stretching and fastening vibration. Satellite peaks arise due to the transition from ligand (O 2p) to metal (Ce 4f) achieved during the primary and main photo-ionization process. This suggests that the valence states of Ce3+ and Ce4+ provide access to the CeO2 lattice sites. The I-V properties of p-Si/n-MDC/Al devices show behavior limited by the properties of the inorganic semiconductor substrate and the size of the hetero-interface energy barrier. The switching voltage of the hetero-junction was found to be approximately 2.4 V.

Hydrogen diffusion in cerium oxide thin films fabricated by pulsed laser deposition

Cerium oxide (CeO2) is well known to be reducible by hydrogen (H2), yet the diffusion and solution properties of hydrogen in ceria at elevated temperatures have remained challenging to evaluate. We therefore fabricated nanometer-thin (∼100 nm) cerium oxide films on Si(111) substrates by pulsed laser deposition (PLD) and quantitatively investigated the H depth distributions therein by means of resonant 1H(15N,αγ)12C nuclear reaction analysis (NRA) before and after annealing in H2 gas at 773–973 K. X-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS) and scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS) reveal that the as-deposited films exhibit single phase CeO2 structure and partially reduced stoichiometry (CeO1.69). H2 annealing does not largely change the H content of the as-deposited films; in all conditions several atomic percent of hydroxyl (OH) are found to exist in a thin (∼4 nm) surface layer, whereas stably bound hydrogen in the bulk of the films is almost uniformly distributed and of much smaller quantity (∼0.2 at.%) than the oxygen vacancy concentration in the partially reduced ceria. Its low concentration and high thermal stability identify this bulk H species as likely being strongly bound to defects in the polycrystalline films rather than as a hydride species that interacts weakly with O-vacancies. The H diffusion coefficient and activation energy in the ceria films are determined as > 10−18 m2 s−1 at 773–973 K and <1.69 eV, respectively. The observed diffusion activation energy is somewhat larger than theoretical predictions for thermal diffusion of H in stoichiometric bulk CeO2, suggesting that defects and oxygen vacancies in the PLD-fabricated ceria thin films possibly have an impact on the H mobility.

Interaction of Water with Ceria Thin Film

AbstractWater interaction with ceria is a fundamental process underpinning catalytic reactions such as water‐gas‐shift and water electrolysis. This review summarizes the investigations of water interactions with the ceria low‐index surfaces [(111), (100), and (110)]. The first part introduces: (a) The atomic structures of the stoichiometric CeO2 and reduced CeOx (x=1.5∼2) thin films, including the characteristics of oxygen vacancies; (b) The anisotropic migration mechanisms of oxygen vacancies and the locations of the entangled polarons in the reduced ceria. The second part reviews water‘s adsorption, desorption, dissociation, and redox properties on the ceria low‐index surfaces studied by DFT, TPD, XPS, RPES, TEM, and SPM methods. The impacts of water coverage, ceria film thickness, strain effect, dopant effect, face stability, and solid‐liquid interface on the interaction between water and ceria are also discussed. At last, this review sheds some light on the future directions and challenges in this topic.

Fabrication of praseodymium-doped ceria (PDC) films by slurry spin-coating technique and its structural, morphological and optical properties

The current study is on the fabrication of PDC films prepared by slurry spin-coating technique for photoluminescence activity. At lower spin rates (1000 rpm), thicker and uniform PDC films were obtained. The structural evolution of the sintered PDC films on a dense alumina substrate was studied using Grazing Incidence X-ray diffraction (GIXRD) and Raman Spectroscopy. Crystallite size, microstrain, and dislocation density values remain almost the same with the increase in the coating cycles. The A568/A463 ratio for 3, 5, and 10 coating cycles are 0.52, 0.49, and 0.61, respectively. Surface roughness studies of PDC films using a 3D Noncontact Profilometer. The mean surface roughness values are 12.55, 13.74, and 22.25 μm for the 3rd,5th, and 10th coating cycles, respectively. Microstructure observation by Field Emission Scanning Electron Microscope (FE-SEM). The average thickness of the films for the 3rd, 5th, and 10th coating cycles are 50.93, 41.64, and 109.95 μm, respectively. The PDC films obtained on a dense alumina substrate were porous. FE-SEM micrographs showed a particle aggregation of several irregular and smaller grains, indicating the sintering activity of PDC films. Optical properties were studied using ultraviolet-visible (UV–Vis) absorption spectra and photoluminescence spectra (PLS). The band gap values slightly increased with the increase in the coating cycles. A decrease in PL intensity with an increase in the coating cycle is related to higher oxygen vacancy concentration. PDC films fabricated by the slurry spin-coating technique can be successfully used for optoelectronic applications.

Chemical expansion of CeO2−δ and Ce0.8Zr0.2O2−δ thin films determined by laser Doppler vibrometry at high temperatures and different oxygen partial pressures

The chemical expansion of ceria (CeO2−δ) and ceria-zirconia (Ce0.8Zr0.2O2−δ, CZO80) thin films is investigated by high-temperature laser Doppler vibrometry (LDV) at temperatures from 600 to 950 °C. The films are deposited on single-crystalline 8 mol-% yttria-stabilized zirconia substrates, which act as pumping cells to adjust oxygen non-stoichiometry in the thin films. Oxygen deficiency causes film expansion, leading to mechanical strain that bends the sample. The total displacement, i.e., the sum of bending and film-thickness change, is determined contact-less by LDV. A differential laser Doppler vibrometer (D-LDV) is realized to enable measurements on a very long time scale, which is necessary due to the long equilibrium times of the ceramic films. These displacements are compared to those acquired with a commercial single-point laser Doppler vibrometer (SP-LDV) for motions above 1 Hz. Here, both devices yield similar results. CZO80 films are found to bend a substrate much more than ceria films under similar experimental conditions. A model describing the displacement of the sample is derived from the Stoney model and applied to calculate deflections using literature data. The displacements at the center of the CZO80 sample measured with the SP-LDV increase from 0.18 nm at 10 Hz and 600 °C to 32.7 nm at 0.1 Hz and 800 °C. For ceria, the displacements range from 1.6 nm (10 Hz, 800 °C) to 79.4 nm (0.1 Hz, 900 °C). The D-LDV enables the detection of quasi-static displacements at very low frequencies. The ceria sample exhibits 218 nm at 0.001 Hz and 800 °C.

Synthesis of ceria nanosheets on the surface of Ce(NO3)3 solution by interaction with gaseous ammonia

The surfactant-free synthesis of a solid film of ceria was carried out at the air–water interface from an aqueous solution of Ce(NO3)3 and gaseous NH3 as reactants. The synthesized CeO2−x • n H2O film consists of 2D nanocrystals with a fluorite structure. The film can form a planar coating on the surface of a solid substrate or transform into curved fragments upon drying, depending on the synthesis conditions.

Polaronic defects in monolayer CeO2: Quantum confinement effect and strain engineering.

We uncover the structure, stability, and electronic properties of polaronic defects in monolayer (ML) CeO2 by means of first-principles calculations, with special attention paid to the quantum confinement effect induced by dimensionality reduction. Results show that the polaron can be more stabilized in ML CeO2 than in the bulk, while formation of oxygen vacancy (Vo2+) and polaron-vacancy complexes [(Vo2+-1polaron)1+, (Vo2+-2polaron)0] tends to be more difficult. The polaronic defect states sit deeper in energy within the bandgap of ML CeO2 compared to the bulk case. We further demonstrate that the epitaxial strain in ceria film, as normally exists when grown on metal substrate, plays a crucial role in regulating the defect energetics and electronic structures. In particular, the formation energies of polarons, Vo2+, (Vo2+-1polaron)1+, and (Vo2+-2polaron)0, generally decrease with tensile strain, leading to controllable defect concentration with strain and temperature. This study not only provides physical insights into the polaronic defects in ultrathin oxide films, but also sheds light on their potential technological applications in nanoelectronics, fuel cells, and catalysts.

Ink formulation and printing of electrolyte for a doped ceria solid oxide fuel cell

• Synthesis of highly printable ceria-based electrolyte for a solid oxide fuel cell. • Polymeric 20 mol% gadolinium-doped ceria nanoparticle ink formulated. • Printed gadolinium-doped ceria films of thickness 130 nm obtained. • Proper adjustment of ink rheology and particle size ensures successful printing. We propose a simple ink formulation and a rapid preparation technique to deposit a 20 mol% gadolinium-doped ceria electrolyte utilizing nanopowders and a polymeric dispersant. The ink was assessed for printability and was successfully printed using a piezoelectric inkjet materials printer. The ejected drops were investigated using built-in stroboscopic imaging during ejection, and the deposited thin films were characterised using optical microscopy and surface profilometry. Inkjet material deposition provides a highly repeatable process for the fabrication of solid oxide fuel cells (SOFCs) that can be up-scaled to industrial levels.

Oxygen vacancy concentration in nanoobjects of CeO2−δ: Effects of characteristic size, morphology, and temperature

A theoretical model has been developed that adequately describes the formation of oxygen vacancies in ceria at the nanoscale. The intrinsic regime of vacancy formation under equilibrium conditions is considered. An analytical relation describing the dependence of the enthalpy of oxygen vacancy formation on the characteristic size and morphology of nanoobjects is derived. This made it possible to perform quantitative calculations of the concentration of oxygen vacancies in cerium oxide nanoobjects for a wide range of their characteristic sizes, morphology and temperature. It is shown that the size effect becomes noticeable for the concentration of surface and bulk oxygen vacancies, approximately, at the characteristic sizes of nanoobjects less than 20 nm and 30 nm, respectively. The effect of morphology on the concentration of oxygen vacancies increases with a decrease in the characteristic size of nanoobjects. This effect is more significant for the concentration of bulk oxygen vacancies than for the concentration of surface oxygen vacancies. In addition, the morphological effect and the size-effect decrease with increasing temperature. In thin films of ceria, the concentration of bulk oxygen vacancies at 300 K is 1011 and 103 times lower than that of spherical ceria nanoparticles, with their characteristic size of 4 nm and 40 nm, respectively. At 1000 K, this ratio is 3∙103 and 7, respectively. Thus, the oxygen storage capacity is higher for spherical nanoparticles and increases with a decrease in their characteristic size.

Al2O3 Toughening ScSZ Electrolyte Fabricated by Water-Based Tape Casting Technique for Solid Oxide Fuel Cells

Abstract A water-based tape-casting slurry is reported to prepare the ceria and scandia co-doped zirconia (ScSZ) electrolyte films. The slurry is characterized and optimized through Zeta potential and rheological property measurements. Smooth and flat ScSZ electrolyte films are obtained by improving the sintering process. The microstructure, electrical performance, and mechanical property of ScSZ with adding different contents of Al2O3 are also investigated. The results show that a proper amount of Al2O3 has a beneficial effect on the densification of ScSZ. A significant decrease in the grain boundary resistance of ScSZ is observed by adding 0.5 wt% Al2O3. The bending strength of the sample with 0.5 wt% Al2O3 (ScSZ-0.5A) is about 400 MPa, which is 20% higher than pure ScSZ. The ScSZ-0.5A electrolyte film fabricated by the water-based tape-casting method shows appropriate electrical conductivity and high mechanical strength, which is promising for practical application in solid oxide fuel cells (SOFCs).

High-throughput and versatile design for multi-layer coating deposition using lab automation through Arduino-controlled devices.

Laboratory and experimental scale manufacturing processes are limited by human error (e.g., poor control over motion and personal subjectivity), especially under fatiguing conditions involving precise, repetitive operations, incurring compounding errors. Commercial layer-by-layer (LbL) automation devices are prohibitively high-priced (especially for academic institutions) with limited flexibility in form factor and potentially software-associated constraints/limitations. In this work, a novel automated multi-beaker dip coater was fabricated to facilitate nano cerium oxide/polymer coatings via an LbL dip coating process and the synthesis of nano ceria films via a novel successive ionic layer adsorption and reaction method on a glass substrate. Automation of tasks, such as those mediating the detailed procedures, is essential in producing highly reproducible, consistent products/materials as well as in reducing the time commitments for laboratory researchers. Herein, we detail the construction of a relatively large, yet inexpensive, LbL coating instrument that can operate over 90cm in the horizontal axis, allowing, for example, up to eight 200 ml beakers with accompanying stir plates. The instrument is operated by simple "off-the-shelf" electronics to control the path and timing of the samples with open-source software while providing precision at ±0.01mm. Furthermore, 3D-printed components were used to maximize the number of substrates that could be coated simultaneously, further improving the sample production rate and reducing waste. Further possibilities for automation beyond the detailed device are provided and discussed, including software interfaces, physical control methods, and sensors for data collection/analysis or for triggers of automated tasks.

Nanostructured Mn-doped CeO2 thin films with enhanced electrochemical properties for pseudocapacitive applications

Cerium oxides with variable oxidation states, high interfacial charge transfer rate have demonstrated to be a potential pseudocapacitive material. In this paper, we present the structural and electrochemical properties of undoped and Mn-doped CeO2synthesized using successive ionic layer adsorption and reaction(SILAR) method. The structural results as obtained from x-ray diffraction (XRD) confirmed the cubic fluorite structure of CeO2 which was unaltered despite the doping concentration. However, a tensile strain of ~2.3% was observed due to ionic radii difference. The topography showed a porous network of nanograins, accounting for strong redox interfacial charge transfer. A specific capacitance of 690 Fg−1 was obtained for 5 wt% Mn-doped CeO2, from cyclic voltammetry curve at a scan rate of 10 mV/s. This value is considerably higher than what was obtained for the undoped ceria, indicating that doping with Mn improved the electrochemical performance of the ceria films.

Synergistic inhibition of cerium and alkyl phosphate composite adlayer on pitting corrosion of Al–Mg–Si aluminium alloy

ABSTRACT The nucleation, propagation, and rehabilitation of pitting corrosion of Al–Mg–Si Aluminium alloy (AA6063) are studied in 3%NaCl solution by using electrochemical noise measurement. It shows that the composite film composed of sequent precipitation of ceria and 1-tetradecylphosphonic acid (DPA) presents the best pitting corrosion resistance compared with the independent ceria conversion film or self-assembling DPA film. XPS and microscopic Raman spectra confirmed that Ceria film is an excellent interlayer for the self-assembling of alkyl phosphate on the intermetallic particles in Al alloy. The anti-corrosion performance of Cerium oxides and DPA composite film is totally dependent on the deposition sequence. Prior deposition of ceria and then DPA film can increase the hydrophilicity of Al matrix and AlFeSi intermetallic particles, further promoting the self-assembling of upper DPA molecules, thus dramatically improving the overall and pitting corrosion resistance of AA6063. This could be attributed to the synergistic effects between the upper DPA film and underlying Ce conversion film. On the contrary, Prior assembly of DPA and then deposition of ceria, may significantly degrade their inhibition efficiency.

Electronic structure of reduced CeO2(111) surfaces interacting with hydrogen as revealed through electron energy loss spectroscopy in comparison with theoretical investigations

Based on both, ab-initio cluster calculations as well as periodic density functional based loss function calculations, we have assigned the origins of the valence electron excitation regime in electron energy loss spectra of well-ordered ceria films in (111) orientation at various states of reduction as well as after exposing the reduced films to hydrogen from the gas phase (Li et al, Angew. Chem. Int. Ed., 58 (2019) 14686–14693). The explicit calculation of intensity distributions using the dipole approximation allow us to draw conclusions about the nature of oxygen vacancies, which occur upon reduction and how those interact with hydrogen to form hydride species.The present study also reports a brief discussion of vibrational excitations of hydrogen loaded ceria and corroborates previous interpretations, based on inelastic neutron scattering.

High Pressure X-ray Diffraction as a Tool for Designing Doped Ceria Thin Films Electrolytes

Rare earth-doped ceria thin films are currently thoroughly studied to be used in miniaturized solid oxide cells, memristive devices and gas sensors. The employment in such different application fields derives from the most remarkable property of this material, namely ionic conductivity, occurring through the mobility of oxygen ions above a certain threshold temperature. This feature is in turn limited by the association of defects, which hinders the movement of ions through the lattice. In addition to these issues, ionic conductivity in thin films is dominated by the presence of the film/substrate interface, where a strain can arise as a consequence of lattice mismatch. A tensile strain, in particular, when not released through the occurrence of dislocations, enhances ionic conduction through the reduction of activation energy. Within this complex framework, high pressure X-ray diffraction investigations performed on the bulk material are of great help in estimating the bulk modulus of the material, and hence its compressibility, namely its tolerance toward the application of a compressive/tensile stress. In this review, an overview is given about the correlation between structure and transport properties in rare earth-doped ceria films, and the role of high pressure X-ray diffraction studies in the selection of the most proper compositions for the design of thin films.

20-nm-Nanogap oxygen gas sensor with solution-processed cerium oxide

Pt-based nanogap electrodes with a gap separation of 20 nm were prepared by electron-beam lithography (EBL). These electrodes were employed to fabricate nanogap gas sensors by combining solution-processed cerium oxide (ceria, CeO2) as the sensing material. Two types (bottom- and top-contact) of nanogap gas sensors were prepared by alternating the EBL and the solution process. Oxygen gas responses were investigated as functions of the gap separation, ceria film thicknesses, and operating temperatures. The sensor response strongly depended on the gap separation and the nanostructure of the cerium oxide film. In the cases of the small gap separation below 35 nm, the nanogap gas sensor exhibits a fast response time of 10 s at a relatively low operating temperature of 573 K; this response time is approximately three orders of magnitude shorter than that exhibited by a microgap sensor under the same measurement conditions. The nanogap gas sensor could also be in use at 1 atm. The improved sensor performance is attributed to the extremely small gap separation of the nanogap electrodes; the reduced gap separation facilitates electron hopping conduction in the ceria film. The proposed approach for fabricating robust and ultrafine nanogap electrodes together with a facile coating method for forming the sensing layer opens up possibilities to develop various nanogap gas sensors with a fast response time.

Oxide-water interaction and wetting property of ceria surfaces tuned by high-temperature thermal aging

The high transmittance, environmentally robust, and unique interaction with water make lanthanide series rare-earth oxides promising for various applications such as next-generation self-cleaning coatings. However, the underlying mechanism of the anomalous hydrophobicity in lanthanide oxides remains controversial due to the lack of molecular-level studies in a well-controlled environment, which greatly limits the possibility to engineer their wettability for broader technical applications. Here, we systematically studied the mechanism that governs the wetting behaviors of ceria films by in-situ X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, and water contact angle measurements under the environmentally controlled conditions. It was found that the hydrophobicity of ceria was mainly contributed by the adsorbed hydrocarbon, and the wettability could be enhanced on cleaner ceria surfaces with more degree of hydroxylation. Based on the significant dependence of wetting property on surface contamination, we further developed an in-situ annealing method to significantly improve the water-splitting performance of ceria powders by removing hydrocarbon contamination. These results suggest that the removal of surface contamination by high-grade oxidation is the key factor to facilitate the water dissociation of ceria films, providing new insights into the control of their wetting property and design of high-performance devices based on ceria films.