Hydration, oxidation, and reduction of GdBaCo<sub>2</sub>O<sub>5.5</sub>from first-principles

Coulaud, Esther; Dezanneau, G.; Geneste, Grégory

doi:10.1039/c5ta05388a

Cited by 20 publications

(9 citation statements)

References 69 publications

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“…As discussed in more detail below, this might be related to a higher covalency of CoO bonds compared with FeO, and a respective decrease of oxide‐ion basicity. The observation of unfavorable hydration thermodynamics for cobalt‐rich perovskites is in good agreement with the fact that for the closely related GdBaCo 2 O 5.5 layered double perovskite, positive hydration enthalpies were found in ab initio calculations …”

Section: Resultssupporting

confidence: 86%

Mixed‐Conducting Perovskites as Cathode Materials for Protonic Ceramic Fuel Cells: Understanding the Trends in Proton Uptake

Zohourian

Merkle

Raimondi

et al. 2018

Adv Funct Materials

243

227

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The proton uptake of 18 compositions in the perovskite family (Ba,Sr,La)(Fe,Co,Zn,Y)O 3-δ , perovskites, which are potential cathode materials for protonic ceramic fuel cells (PCFCs), is investigated by thermogravimetry. Hydration enthalpies and entropies are derived, and the doping trends are explored. The uptake is found to be largely determined by the basicity of the oxide ions. Partial substitution of Zn on the B-site strongly enhances proton uptake, while Co substitution has the opposite effect. The proton concentration in Ba 0.95 La 0.05 Fe 0.8 Zn 0.2 O 3-δ is found to be 10% per formula unit at 250 °C, 5.5% at 400 °C, and 2.3% at 500 °C, which are the highest values reported so far for a mixed-conducting perovskite exhibiting hole, proton, and oxygen vacancy transport. A comprehensive set of thermodynamic data for proton uptake in (Ba,Sr,La)(Fe,Co,Zn,Y)O 3-δ is determined. Defect interactions between protons and holes partially delocalized from the B-site transition metal to the adjacent oxide ions decrease the proton uptake. From these results, guidelines for the optimization of PCFC cathode materials are derived.

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Section: Resultssupporting

confidence: 86%

Mixed‐Conducting Perovskites as Cathode Materials for Protonic Ceramic Fuel Cells: Understanding the Trends in Proton Uptake

Zohourian

Merkle

Raimondi

et al. 2018

Adv Funct Materials

243

227

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“…The concurrent increase in the concentration of O OH and O surface (Figure 7 and Figure S15) and in particular the decrease in the concentration of O defect imply that defects are involved in water dissociation, resulting in filling the vacancies and forming OH groups. 70 Finally, the peak at 533.2 eV is attributed to adsorbed molecular water. The weak tail in the range observed at room temperature between 534 and 535 eV is assigned to very small amounts of adsorbed oxygen-containing surface species, respectively.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…The contribution exhibits the most distinct increase in a wet feed, which further supports the assignment (Figure and Figure S15). The concurrent increase in the concentration of O OH and O surface (Figure and Figure S15) and in particular the decrease in the concentration of O defect imply that defects are involved in water dissociation, resulting in filling the vacancies and forming OH groups …”

Section: Resultsmentioning

confidence: 99%

Surface Conditions That Constrain Alkane Oxidation on Perovskites

et al. 2020

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The crystal structure of perovskites can incorporate a wide variety of cations, which makes this class of materials so interesting for studies of links between solid-state chemistry and catalysis. Perovskites are known as typical total combustion catalysts in hydrocarbon oxidation reactions. The fundamental question that we investigate here is whether surface modifications of perovskites can lead to the formation of valuable reaction products in alkane oxidation. We studied the effect of segregated two-dimensional surface nanostructures on selectivity to propene in the oxidative dehydrogenation of propane. Manganese-based perovskites AMnO 3 (A = La, Sm) were prepared by combustion and hydrothermal synthesis. Bulk and surface structures were investigated by X-ray diffraction, temperature-programmed reduction, aberration-corrected scanning transmission electron microscopy (STEM), multiwavelength Raman, and ambient-pressure X-ray photoelectron spectroscopy (AP-XPS) in combination with near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. Surface oxygen species responsible for C−H activation were distinguished by AP-XPS on the basis of a rigorous in situ analysis of the O 1s spectra recorded under a broad range of reaction conditions. Signals at 529.2, 530.1, 530.9, 531.2, and 531.8 eV were attributed to lattice O, defect-affected O, surface O, oxygen in carbonates, and hydroxyl groups, respectively. Operando AP-XPS revealed critical surface features, which occur under catalyst operation. The catalyst performance depends on the synthesis technique and the reaction conditions. In presence of a two-dimensional MnO x surface phase, addition of steam to the feed resulted in an increase in selectivity to the partial oxidation product propene to practically relevant values. The selectivity increase is related to the presence of Mn in a low oxidation state (2+/3+), an increased concentration of hydroxyl groups, and a higher abundance of adsorbed activated oxygen species on the catalyst surface. The surface analysis of a working catalyst highlights the importance of the termination layer of polycrystalline perovskites as a genuine property implemented by catalyst preparation. Such a termination layer controls the chemical properties and reactivity of perovskites. The information provides input for the development of realistic models that can be used by theory to predict functional properties.

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“…In addition to this overall trend, the degree of hydration varies strongly with the cation composition of the perovskite host . So far, only a few theoretical studies have dealt with proton incorporation into PCFC cathode perovskites and related materials. ,− In particular, the dependence of hydration thermodynamics on the concentration of electron holes, which clearly shows up in experimental data, has not yet been investigated by ab initio calculations. This is in contrast to unprotonated Fe and Co perovskites, for which the variation of V O •• formation energies with hole concentration has been reported, e.g., in refs − .…”

Section: Introductionmentioning

confidence: 99%

Interdependence of Oxygenation and Hydration in Mixed-Conducting (Ba,Sr)FeO_3−δ Perovskites Studied by Density Functional Theory

et al. 2020

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Protonic–electronic mixed-conducting perovskites are relevant as cathode materials for protonic ceramic fuel cells (PCFCs). In the present study, the relation between the electronic structure and the thermodynamics of oxygen nonstoichiometry and hydration is investigated for BaFeO3−δ and Ba0.5Sr0.5FeO3−δ by means of density functional theory. The calculations are performed at the PBE + U level and yield ground-state electronic structures dominated by an oxygen-to-metal charge transfer with electron holes in the O 2p valence bands. Oxygen nonstoichiometry is modeled for 0 ≤ δ ≤ 0.5 with oxygen vacancies in doubly positive charge states. The energy to form an oxygen vacancy is found to increase upon reduction, i.e., decreasing concentration of ligand holes. The higher vacancy formation energy in reduced (Ba,Sr)FeO3−δ is attributed to a higher Fermi level at which electrons remaining in the lattice from the removed oxide ions have to be accommodated. The energy for dissociative H2O absorption into oxygen vacancies is found to vary considerably with δ, ranging from ≈−0.2 to ≈−1.0 eV in BaFeO3−δ and from ≈0.2 to ≈−0.6 eV in Ba0.5Sr0.5FeO3−δ. This dependence is assigned to the annihilation of ligand holes during oxygen release, which leads to an increase in the ionic charge of the remaining lattice oxide ions. The present study provides sound evidence that p-type electronic conductivity and the susceptibility for H2O absorption are antagonistic properties since both depend in opposite directions on the concentration of ligand holes. The reported trends regarding oxygenation and hydration energies are in line with the experimental observations.

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Hydration, oxidation, and reduction of GdBaCo₂O_5.5from first-principles

Abstract: Structural, magnetic and chemical properties of GdBaCo2O5.5 regarding hydration, oxidation and reduction are studied by density-functional calculations in the DFT + U formalism.

Cited by 20 publications

References 69 publications

Mixed‐Conducting Perovskites as Cathode Materials for Protonic Ceramic Fuel Cells: Understanding the Trends in Proton Uptake

Mixed‐Conducting Perovskites as Cathode Materials for Protonic Ceramic Fuel Cells: Understanding the Trends in Proton Uptake

Surface Conditions That Constrain Alkane Oxidation on Perovskites

Interdependence of Oxygenation and Hydration in Mixed-Conducting (Ba,Sr)FeO_3−δ Perovskites Studied by Density Functional Theory

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Hydration, oxidation, and reduction of GdBaCo2O5.5from first-principles

Abstract: Structural, magnetic and chemical properties of GdBaCo2O5.5 regarding hydration, oxidation and reduction are studied by density-functional calculations in the DFT + U formalism.

Cited by 20 publications

References 69 publications

Mixed‐Conducting Perovskites as Cathode Materials for Protonic Ceramic Fuel Cells: Understanding the Trends in Proton Uptake

Mixed‐Conducting Perovskites as Cathode Materials for Protonic Ceramic Fuel Cells: Understanding the Trends in Proton Uptake

Surface Conditions That Constrain Alkane Oxidation on Perovskites

Interdependence of Oxygenation and Hydration in Mixed-Conducting (Ba,Sr)FeO3−δ Perovskites Studied by Density Functional Theory

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Hydration, oxidation, and reduction of GdBaCo₂O_5.5from first-principles

Interdependence of Oxygenation and Hydration in Mixed-Conducting (Ba,Sr)FeO_3−δ Perovskites Studied by Density Functional Theory