High-surface-area ceria prepared by ALD on Al2O3 support

Onn, Tzia Ming; Zhang, Shuyi; Arroyo‐Ramírez, Lisandra; Xia, Ye; Wang, Cong; Pan, Xiaoqing; Graham, George W.; Gorte, Raymond J.

doi:10.1016/j.apcatb.2016.08.054

Cited by 59 publications

(58 citation statements)

References 43 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Figure 4b shows differential rates for the same materials after the supports had been calcined to 1073 K. The only catalyst affected by this treatment was the Pd/CeO2 sample. The loss of activity in this sample is likely due to loss of the CeO2 surface area, as reported previously for a similar Pd/CeO2 catalyst used for the WGS reaction [23]. The Pd/ZrO2 and Pd/20ZrO2/ZrO2 catalysts were not affected because the reaction only occurs on the Pd phase.…”

Section: Resultssupporting

confidence: 49%

Stabilization of ZrO2 Powders via ALD of CeO2 and ZrO2

et al. 2017

View full text Add to dashboard Cite

ZrO 2 powders were modified by atomic layer deposition (ALD) with CeO 2 and ZrO 2 , using Ce(TMHD) 4 and Zr(TMHD) 4 as the precursors, in order to determine the effect of ALD films on the structure, surface area, and catalytic properties of the ZrO 2 . Growth rates were measured gravimetrically and found to be 0.017 nm/cycle for CeO 2 and 0.031 nm/cycle for ZrO 2 . The addition of 20 ALD cycles of either CeO 2 or ZrO 2 was found to stabilize the surface area of the ZrO 2 powder following calcination to 1073 K and to suppress the tetragonal-to-monoclinic transition. Shrinkage of ZrO 2 wafers was also suppressed by the ALD films. When used as a support for Pd in CO oxidation, the CeO 2 -modified materials significantly enhanced rates due to interactions between the Pd and the CeO 2 . Potential applications for modifying catalyst supports using ALD are discussed.

show abstract

Section: Resultssupporting

confidence: 49%

Stabilization of ZrO2 Powders via ALD of CeO2 and ZrO2

et al. 2017

View full text Add to dashboard Cite

show abstract

“…Previously published microscopy results on γ-Al 2 O 3 suggest that the deposited films uniformly cover the surface of the γ-Al 2 O 3 and have a thickness close to that calculated by the weight changes. 15,16 Based on these measurements, the growth rates were determined to be 0.024 nm ZrO 2 /cycle, 0.019 nm La 2 O 3 /cycle, and 0.018 nm Fe 2 O 3 /cycle. To demonstrate that these growth rates are not strongly dependent on the substrate, measurements were also performed for Fe 2 O 3 deposition on a 0.5-g sample of LSF powder with a surface area of 6 m 2 /g.…”

Section: Methodsmentioning

confidence: 99%

“…12,[15][16][17] The system is essentially an adsorption apparatus that can be evacuated with a mechanical pump to approximately 10 −3 torr. The system consists of separate chambers for the substrate and two precursors, separated by high-temperature valves.…”

Section: Methodsmentioning

confidence: 99%

Modification of LSF-YSZ Composite Cathodes by Atomic Layer Deposition

Rahmanipour

Cheng

Onn

et al. 2017

J. Electrochem. Soc.

View full text Add to dashboard Cite

Composite, Solid-Oxide-Fuel-Cell (SOFC) electrodes of La 0.8 Sr 0.2 FeO 3 (LSF) and yttria-stabilized zirconia (YSZ) were prepared by infiltration methods and then modified by Atomic Layer Deposition (ALD) of ZrO 2 , La 2 O 3 , Fe 2 O 3 , or La 2 O 3 -Fe 2 O 3 codeposited films of different thicknesses to determine the effect of surface composition on cathode performance. Film growth rates for ALD performed using vacuum procedures at 573 K for Fe 2 O 3 and 523 K for ZrO 2 and La 2 O 3 were determined to be 0.024 nm ZrO 2 /cycle, 0.019 nm La 2 O 3 /cycle, and 0.018 nm Fe 2 O 3 /cycle. For ZrO 2 and Fe 2 O 3 , impedance spectra on symmetric cells at 873 K indicated that polarization resistances increased with coverage in a manner suggesting simple blocking of O 2 adsorption sites. With La 2 O 3 , the polarization resistance decreased with small numbers of ALD cycles before again increasing at higher coverages. When La 2 O 3 and Fe 2 O 3 were co-deposited, the polarization resistances remained low at high film coverages, implying that O 2 adsorption sites were formed on the co-deposited films. The implications of these results for future SOFC electrode development are discussed. Atomic Layer Deposition (ALD) is attracting an increasing level of attention as a method for modifying SOFC electrodes because the surface composition can be modified with unparalleled precision. 1-11Uniform, atomic-scale films are formed in ALD by repeated cycles in which the surface is first allowed to react with an organometallic precursor, followed by a subsequent oxidation step. Since the reaction of the precursor with the surface is performed under conditions which limit the extent of reaction to one monolayer at most, the thickness of the final oxide film can be precisely controlled by the number of cycles.In the case of SOFC cathodes, ALD has been used to improve both electrode stability and decrease impedance.1-4 For example, Gong et al. reported that degradation rates for cathodes based on La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ (LSCF) decreased significantly after depositing a 5-nm ZrO 2 film.3,4 While they reported a slight increase in the initial electrode impedance, the performance of the ALD-modified electrode surpassed that of the unmodified electrode after less than 100 h and exhibited a much lower impedance after 900 h of operation at 1073 K. In another example of cathodes modified by ZrO 2 ALD films, the initial impedance of composite cathodes of Sr-doped LaMnO 3 (LSM) and yttria-stabilized zirconia (YSZ) actually decreased following deposition of films as thick as 60 nm. 6 This latter study is particularly revealing because it had been previously reported that infiltration of CoO x nanoparticles could be used to decrease cathode polarization.13 Choi et al. suggested that addition of CoO x by ALD differs from infiltration because infiltration produces inhomogeneous layers that affect surface area and because the infiltration process may induce changes in the cathode morphology. 6 In principle, ALD allows catalytic materials to ...

show abstract

“…However, since only a few ALD cycles are required to reach substantial weight loadings (see Section 1.4), long exposure and purge times (on the order of 10's of minutes or perhaps even hours) may be acceptable, as demonstrated by the fixed bed static reactor design developed by researchers at BASF [56]. It should be noted that exposure times can be shortened by using agitated or rotating bed reactors [44,66,67], using thin pelletized samples (Figure 3) [70][71][72][73], and increasing precursor partial pressures [56,57].…”

Section: Ald Reactor Designs For Catalysts and Sofc Electrodesmentioning

confidence: 99%

“…The term "static" is used here to refer to the sample inside the reactor being exposed to non-flowing (i.e., static) precursors. The reactor itself can be rotating, or the particles inside the reactor can be agitated in various other ways [44,66,67], although simple static reactors without any moving parts have successfully been used to coat catalysts and SOFC electrodes [68][69][70][71][72][73][74][75]. In a static reactor, the sample is held in a sealed vessel that can be evacuated.…”

Section: Ald Reactor Designs For Catalysts and Sofc Electrodesmentioning

confidence: 99%

Atomic Layer Deposition on Porous Materials: Problems with Conventional Approaches to Catalyst and Fuel Cell Electrode Preparation

et al. 2018

View full text Add to dashboard Cite

Atomic layer deposition (ALD) offers exciting possibilities for controlling the structure and composition of surfaces on the atomic scale in heterogeneous catalysts and solid oxide fuel cell (SOFC) electrodes. However, while ALD procedures and equipment are well developed for applications involving flat surfaces, the conditions required for ALD in porous materials with a large surface area need to be very different. The materials (e.g., rare earths and other functional oxides) that are of interest for catalytic applications will also be different. For flat surfaces, rapid cycling, enabled by high carrier-gas flow rates, is necessary in order to rapidly grow thicker films. By contrast, ALD films in porous materials rarely need to be more than 1 nm thick. The elimination of diffusion gradients, efficient use of precursors, and ligand removal with less reactive precursors are the major factors that need to be controlled. In this review, criteria will be outlined for the successful use of ALD in porous materials. Examples of opportunities for using ALD to modify heterogeneous catalysts and SOFC electrodes will be given.

show abstract

High-surface-area ceria prepared by ALD on Al2O3 support

Cited by 59 publications

References 43 publications

Stabilization of ZrO2 Powders via ALD of CeO2 and ZrO2

Stabilization of ZrO2 Powders via ALD of CeO2 and ZrO2

Modification of LSF-YSZ Composite Cathodes by Atomic Layer Deposition

Atomic Layer Deposition on Porous Materials: Problems with Conventional Approaches to Catalyst and Fuel Cell Electrode Preparation

Contact Info

Product

Resources

About