Oxygen exchange kinetics on systematically doped ceria: a pulsed isotope exchange study

Schaube, Maximilian; Merkle, Rotraut; Maier, Joachim

doi:10.1039/c9ta05908c

Cited by 24 publications

(38 citation statements)

References 87 publications

(140 reference statements)

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“…Our conclusion is consistent with a recent study by Schaube et al The authors investigated the RDS of PCO using a pulsed isotope exchange method, and found molecular oxygen species are involved in the RDS (in addition to oxygen vacancies). 49 We note that in MIECs such as SrTi 1-x Fe x O 3-δ , it has been proposed that minority electronic species, rather than majority, participates in RDS. 34…”

Section: Combinations 262mentioning

confidence: 78%

Constructing a pathway for mixed ion and electron transfer reactions for O2 incorporation in Pr0.1Ce0.9O2−x

et al. 2020

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In interfacial charge-transfer reactions, the complexity of the reaction pathway increases with the number of charges transferred, and becomes even greater when the reaction involves both electrons (charge) and ions (mass). These so-called mixed ion electron transfer (MIET) reactions are crucial in intercalation/insertion electrochemistry, such as those occurring in oxygen reduction/evolution electrocatalysts and lithium-ion battery electrodes. Understanding MIET reaction pathways, particularly identifying the rate-determining step (RDS), is crucial for engineering interfaces at the molecular, electronic, and point defect levels. Here we develop a generalizable experimental and analysis framework for constructing the O 2 (g) incorporation reaction pathway in Pr 0.1 Ce 0.9 O 2-x. We converge on four candidate RDS (dissociation of neutral 31 oxygen adsorbate) out of more than 100 possibilities by measuring the current density-32 overpotential curves while controlling both oxygen activity in the solid and the oxygen gas 33 partial pressure, and quantifying the chemical and electrostatic driving forces using operando 34 ambient pressure X-ray photoelectron spectroscopy. 35 36 3 Mixed ion and electron transfer (MIET) reactions involve the transfer of both ionic and electronic charges across interfaces. They are substantially more complex than electron transfer and proton-coupled electron transfer reactions because the ionic charge also crosses the electrochemical double layer. 1 The net reactions are usually chemical in nature (i.e., no net charge transfer). Examples include H + intercalation in layered hydroxides and Li + insertion in 41 metal oxides (Fig. 1a,b). 2 Another ubiquitous example is the oxygen incorporation reaction (OIR) 42 occurring at the solid/gas interface (Fig. 1c). It is rate-determining for many energy-and 43 environment-related technologies, including oxygen storage materials for emission control, 3 44 solid oxide fuel cells (SOFCs), 4 electrolysis cells, 5 thermochemical water splitting cycles, 6 and oxygen permeation membranes. 7 The OIR is expressed as − − + → 2 2 O 4e 2O. (1) 47 Understanding the OIR reaction pathway is crucial for engineering and discovering catalysts, 48 typically oxides, with high activity and stability. 8,9 Mixed ionic-electronic conductors (MIECs) 49 have received widespread interests because they expand the effective OIR site to the gas/solid 50 double-phase boundary beyond the traditional triple phase boundary between gas, ionic and 51 electronic conductors. 10,11 There, oxygen ions and electrons react with oxygen adsorbates at the same active site, resulting in a reaction that involves the transfer of two oxygen ions and four electrons. The number of charges transferred during OIR has made it challenging to isolate the ratedetermining step (RDS). Most experimental work has focused on measuring the exchange coefficients 12 using tracer diffusion, 13 conductivity and mass relaxation, 14 and impedance spectroscopy, 15 as well as their reaction order with respect to oxyge...

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Section: Combinations 262mentioning

confidence: 78%

Constructing a pathway for mixed ion and electron transfer reactions for O2 incorporation in Pr0.1Ce0.9O2−x

et al. 2020

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“…In this case, the conductivity follows the (pO 2 ) −1/4 dependence [18,59,60]. Impurities with higher valence (donors D, e.g., Nb 5+ ) lead to the suppression of V [60].…”

Section: Defect Interactions In Ceo 2−δ and Ce 1−x Zr X O 2−δmentioning

confidence: 98%

“…At relatively low temperatures and low non-stoichiometry, it is considered to be constant, but is substantially larger than that of intrinsic vacancies or electrons generated by the reduction of cerium. In this case, the conductivity follows the ( p O 2 ) −1/4 dependence [ 18 , 59 , 60 ]. Impurities with higher valence (donors D, e.g., Nb 5+ ) lead to the suppression of

and formation of interstitial negatively charged oxygen ions

.…”

Section: Theoretical Background Samples Preparation and Experimenmentioning

confidence: 99%

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Linking the Electrical Conductivity and Non-Stoichiometry of Thin Film Ce1−xZrxO2−δ by a Resonant Nanobalance Approach

et al. 2021

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Bulk ceria-zirconia solid solutions (Ce1−xZrxO2−δ, CZO) are highly suited for application as oxygen storage materials in automotive three-way catalytic converters (TWC) due to the high levels of achievable oxygen non-stoichiometry δ. In thin film CZO, the oxygen storage properties are expected to be further enhanced. The present study addresses this aspect. CZO thin films with 0 ≤ x ≤ 1 were investigated. A unique nano-thermogravimetric method for thin films that is based on the resonant nanobalance approach for high-temperature characterization of oxygen non-stoichiometry in CZO was implemented. The high-temperature electrical conductivity and the non-stoichiometry δ of CZO were measured under oxygen partial pressures pO2 in the range of 10−24–0.2 bar. Markedly enhanced reducibility and electronic conductivity of CeO2-ZrO2 as compared to CeO2−δ and ZrO2 were observed. A comparison of temperature- and pO2-dependences of the non-stoichiometry of thin films with literature data for bulk Ce1−xZrxO2−δ shows enhanced reducibility in the former. The maximum conductivity was found for Ce0.8Zr0.2O2−δ, whereas Ce0.5Zr0.5O2-δ showed the highest non-stoichiometry, yielding δ = 0.16 at 900 °C and pO2 of 10−14 bar. The defect interactions in Ce1−xZrxO2−δ are analyzed in the framework of defect models for ceria and zirconia.

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“…They represent chemically excited states (high energy sites) and substantially increased acid-base or redox activity and, as such, should be naturally considered as the catalytically active centers (see, e.g., refs − ). The importance of point defects and their concentrations for heterogeneous reaction rates has been demonstrated, for example, for the oxygen exchange reaction on Sr(Ti 1– x Fe x )O 3‑δ perovskites ,− or on doped ceria …”

Section: Introductionmentioning

confidence: 99%

Interdependence of Point Defects and Reaction Kinetics: CO and CH₄ Oxidation on Ceria and Zirconia

2020

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The rate of CO and CH4 oxidation is measured on systematically Pr-, Gd-, or Nb-doped ceria, and Y- or Pr-doped zirconia to investigate the impact of point defects on heterogeneously catalyzed oxidation kinetics. The oxidation reactions proceed via the Mars–Van Krevelen mechanism. The CO oxidation rate is found to be independent of dopant content for Pr- and Gd-doped ceria, while it increases with [Pr]tot for Pr-doped zirconia. Under certain conditions (low dopant concentrations and/or low temperatures) the competition between the lattice oxygen consumption by CO and the oxygen replenishment by gaseous O2 decreases the effective oxygen activity (p(O2)eff) inside the catalyst particles by up to 8 orders of magnitude. The increased point defect concentrations in the catalyst accelerate the oxygen incorporation until steady state is reached. Owing to the lower reactivity of CH4, no decreased p(O2)eff was observed for CH4 oxidation. We demonstrate that the contributions of point defect concentrations, which themselves depend on the (effective) oxygen partial pressure, must properly be included in the reaction rate expression to obtain correct apparent reaction orders for CO and O2.

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Oxygen exchange kinetics on systematically doped ceria: a pulsed isotope exchange study

Abstract: 20 systematically doped ceria samples: strong dependence of oxygen exchange rate on dopant concentration, even steeper for redox-active dopants (Pr).

Cited by 24 publications

References 87 publications

Constructing a pathway for mixed ion and electron transfer reactions for O2 incorporation in Pr0.1Ce0.9O2−x

Constructing a pathway for mixed ion and electron transfer reactions for O2 incorporation in Pr0.1Ce0.9O2−x

Linking the Electrical Conductivity and Non-Stoichiometry of Thin Film Ce1−xZrxO2−δ by a Resonant Nanobalance Approach

Interdependence of Point Defects and Reaction Kinetics: CO and CH₄ Oxidation on Ceria and Zirconia

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Oxygen exchange kinetics on systematically doped ceria: a pulsed isotope exchange study

Abstract: 20 systematically doped ceria samples: strong dependence of oxygen exchange rate on dopant concentration, even steeper for redox-active dopants (Pr).

Cited by 24 publications

References 87 publications

Constructing a pathway for mixed ion and electron transfer reactions for O2 incorporation in Pr0.1Ce0.9O2−x

Constructing a pathway for mixed ion and electron transfer reactions for O2 incorporation in Pr0.1Ce0.9O2−x

Linking the Electrical Conductivity and Non-Stoichiometry of Thin Film Ce1−xZrxO2−δ by a Resonant Nanobalance Approach

Interdependence of Point Defects and Reaction Kinetics: CO and CH4 Oxidation on Ceria and Zirconia

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Interdependence of Point Defects and Reaction Kinetics: CO and CH₄ Oxidation on Ceria and Zirconia