Highly Enhanced Concentration and Stability of Reactive Ce<sup>3+</sup> on Doped CeO<sub>2</sub> Surface Revealed In Operando

Chueh, William C.; McDaniel, Anthony H.; Graß, Michael; Hao, Yong; Jabeen, Naila; Liu, Zhi; Haile, Sossina M.; McCarty, K. F.; Bluhm, Hendrik; Gabaly, Farid El

doi:10.1021/cm300574v

Cited by 178 publications

(226 citation statements)

References 71 publications

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“…The strong oxygen-ion gradient is understood as nonequilibrium defect segregation, whereby lowered formation energy at the surface relative to that in the bulk leads to enrichment 24 . During incorporation reaction, the persistent segregation of reactive oxygen vacancy from the bulk to the surface arises from the rapid transport of oxygen vacancies under both WSR and HOR conditions.…”

Section: Resultsmentioning

confidence: 99%

“…Figure 4a,b shows the spectra of valence band and Ce 4d core level normalized to the total Ce 4d intensity (arising from all Ce species). Using two quantification approaches reported previously 24,31 , we determined the surface polaron concentration using the Ce 4f intensity as well as the Ce 4d multiplet splitting. Excellent linear correlation was obtained between the two methods ( Supplementary Fig.…”

Section: Resultsmentioning

confidence: 99%

“…The majority of these work considered the surface and intermediate species at equilibrium. For example, density functional calculations predicted reduced defect formation energy on the low-index surfaces of ceria from that of the bulk [20][21][22][23] , which has been validated experimentally 24 . In operando techniques such as in-situ X-ray photoelectron spectroscopy (XPS) [25][26][27][28][29] have also been applied to ceria 16,[30][31][32] .…”

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confidence: 77%

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Fast vacancy-mediated oxygen ion incorporation across the ceria–gas electrochemical interface

et al. 2014

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Electrochemical incorporation reactions are ubiquitous in energy storage and conversion devices based on mixed ionic and electronic conductors, such as lithium-ion batteries, solidoxide fuel cells and water-splitting membranes. The two-way traffic of ions and electrons across the electrochemical interface, coupled with the bulk transport of mass and charge, has been challenging to understand. Here we report an investigation of the oxygen-ion incorporation pathway in CeO 2-d (ceria), one of the most recognized oxygen-deficient compounds, during hydrogen oxidation and water splitting. We probe the response of surface oxygen vacancies, electrons and adsorbates to the electrochemical polarization at the ceria-gas interface. We show that surface oxygen-ion transfer, mediated by oxygen vacancies, is fast. Furthermore, we infer that the electron transfer between cerium cations and hydroxyl ions is the rate-determining step. Our in operando observations reveal the precise roles of surface oxygen vacancy and electron defects in determining the rate of surface incorporation reactions.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

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confidence: 77%

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Fast vacancy-mediated oxygen ion incorporation across the ceria–gas electrochemical interface

et al. 2014

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“…Recent investigations revealed a high concentration and a high stability of reactive surface Ce 3+ ions over a wide range of temperature and of oxygen partial pressure on ceria surfaces [58], and Ce 3+ and oxygen vacancies are generally believed to be the active sites on ceria surfaces and therefore refer to the Sad adsorption sites [59][60][61]. It is generally assumed that one of the different reaction steps will be rate determining, with the charge transfer step leading to dissociation being the most likely rate determining step [56,62].…”

Section: Oxygen Exchange From Co2 Atmospheresmentioning

confidence: 99%

Ceria: Recent Results on Dopant-Induced Surface Phenomena

et al. 2017

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Abstract:Redox studies on dense zirconia-doped ceria pellets were carried out by thermogravimetric investigations and dilatometry. Up to 1600 K reduction parameters determined by both methods correspond to each other. At higher temperatures, however, thermogravimetry overestimates the degree of reduction since mass loss is not only due to oxygen exsolution but also to selective evaporation of CeO 2 whose vapour pressure is considerably higher than that of ZrO 2 . As a consequence surface segregation of zirconia occurs in (Ce,Zr)O 2−δ pellets leading to a porous surface zone of Ce 2 Zr 2 O 7 pyrochlore which gradually grows in thickness. Surface enrichment of zirconia is detrimental for splitting CO 2 or H 2 O since re-oxidation temperatures of (Ce,Zr)O 2−δ are known to be shifted towards lower temperatures with increasing ZrO 2 content. Thus, very harsh reduction conditions should be avoided for the (Ce,Zr)O 2−δ redox system. The kinetics investigations comprised the high temperature reduction step (T ∼ = 1600 K) and the "low" temperature oxidation reaction with a carbon dioxide atmosphere (T ∼ = 1000 K). The reduction kinetics (at around 1600 K and an oxygen activity of 7 × 10 −4 in the gas phase) directly yield the (reduction) equilibrium exchange rate of oxygen in the order of 10 −7 mol·O/(cm 3 ·s) as the kinetics are surface controlled. The oxidation step at around 1000 K, however, occurs in the mixed control or in the diffusion control regime, respectively. From oxygen isotope exchange in combination with SIMS depth profiling oxygen exchange coefficients, K, and oxygen diffusivities, D, were determined for so-called equilibrium experiments as well as for non-equilibrium measurements. From the obtained values for K and D the (oxidation) equilibrium exchange rates for differently doped ceria samples were determined. Their dependency on the oxygen activity and the nature and the concentrations of a tetravalent dopant (Zr) and trivalent dopants (La, Y, Sm) could be semi-quantitatively rationalised on the basis of a master equation for the equilibrium surface exchange rate.

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“…The catalytic activity of ceria stems from two important aspects: (1) the redox reactions between the two oxidation states of cerium (Ce 3+ vs. Ce 4+ ) accompanied by the formation of oxygen vacancies and (2) the uncommon ability of ceria to retain the cubic crystal structure even when ~ 15% of the lattice oxygen anions are missing [7] [8]. It was shown that the concentration of the reduced cerium cations and oxygen vacancies could be even higher on ceria surfaces [9] than in the bulk. Our recent spectroscopic analysis leads to the speculation that the surface reaction could be the rate-limiting step of hydrogen evolution reaction (HER) on the ceria surface [10].…”

Section: Introductionmentioning

confidence: 99%

Surface structure of coherently strained ceria ultrathin films

et al. 2016

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Cerium oxide, or ceria, is an important material for solid oxide fuel cell and water splitting devices. Although the ceria surface is active in catalytic and electrochemical reactions, how its catalytic properties are affected by the surface structure under operating conditions is far from understood. We investigate the structure of the coherently strained CeO 2 ultrathin films on yttriastabilized zirconia (001) single crystals by specular synchrotron X-ray diffraction (XRD) under oxidizing conditions as a first step to study the surface structure in situ. An excellent agreement between the experiment data and the model is achieved by using a "stacks and islands" model that has a two-component roughness. One component is due to the tiny clusters of nm scale in lateral dimensions on each terrace, while the other component is due to slightly different CeO 2 thickness that span over hundreds of nm on neighboring terraces. We attribute the non-uniform thickness to step de-pairing during the thin film deposition which is supported by the surface morphology results on the microscopic level. Importantly, our model also shows that the polarity of the ceria surface is removed by a half monolayer surface coverage of oxygen. The successful resolution of the ceria surface structure using in situ specular synchrotron XRD paves the way to study the structural evolution of ceria as a fuel cell electrode under catalytically relevant temperatures and gas pressures.

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Highly Enhanced Concentration and Stability of Reactive Ce³⁺ on Doped CeO₂ Surface Revealed In Operando

Cited by 178 publications

References 71 publications

Fast vacancy-mediated oxygen ion incorporation across the ceria–gas electrochemical interface

Fast vacancy-mediated oxygen ion incorporation across the ceria–gas electrochemical interface

Ceria: Recent Results on Dopant-Induced Surface Phenomena

Surface structure of coherently strained ceria ultrathin films

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Highly Enhanced Concentration and Stability of Reactive Ce3+ on Doped CeO2 Surface Revealed In Operando

Cited by 178 publications

References 71 publications

Fast vacancy-mediated oxygen ion incorporation across the ceria–gas electrochemical interface

Fast vacancy-mediated oxygen ion incorporation across the ceria–gas electrochemical interface

Ceria: Recent Results on Dopant-Induced Surface Phenomena

Surface structure of coherently strained ceria ultrathin films

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Highly Enhanced Concentration and Stability of Reactive Ce³⁺ on Doped CeO₂ Surface Revealed In Operando