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One major challenge for the further development of solid oxide fuel cells is obtaining high-performance cathode materials with sufficient stability against reactions with CO2present in the ambient atmosphere. However, the enhanced stability is often achieved by using material systems exhibiting decreased performance metrics. The phenomena underlying the performance and stability trade-off has not been well understood. This paper uses antimony-doped SrFeO3−δas a model material to shed light on the relationship between the structure, stability, and performance of perovskite-structured oxides which are commonly used as cathode materials. X-ray absorption revealed that partial substitution of Fe by Sb leads to a series of changes in the local environment of the iron atom, such as a decrease in the iron oxidation state and increase in the oxygen coordination number. Theoretical calculations show that the structural changes are associated with an increase in both the oxygen vacancy formation energy and metal–oxygen bond energy. The area-specific resistance (ASR) of the perovskite oxide increases with Sb doping, indicating a deterioration of the oxygen reduction activity. Exposure of the materials to CO2leads to depressed oxygen desorption and an increased ASR, which becomes less pronounced at higher Sb doping levels. Origin of the stability-performance trade-off is discussed based on the structural parameters.

Membranes only:A hybrid organic–inorganic membrane for CO2separation is prepared by sol–gel deposition of a microporous ethylene‐bridged silsesquioxane layer onto a multilayer support. Low CO2permeance is imparted by doping acidic niobium centers into the hybrid silica network. The membrane exhibits superior hydrothermal stability with He/CO2selectivities as high as 3700.

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The space charge density at the surface of yttria-stabilised zirconia (YSZ) containing 2–10 mol% yttria was determined from differential capacity measurements of YSZ/gold interfaces at 750–850 K. The oxygen vacancy concentration in the sub-surface layer was determined as a function of temperature and bias potential by fitting the experimental data at positive bias potentials to predictions based on a Boltzmann-type expression. The vacancy concentration at the interface increases with decreasing bias potential, and reaches a temperature-dependent maximum value at negative bias potentials. The thermal activation parameter for this process is 0.27–0.46 eV. A thermodynamic model for the near-surface defect structure of YSZ is proposed, in which oxygen vacancies are assumed to be distributed randomly over a fraction of the total number of oxygen sub-lattice sites. The fraction of sites that is available for oxygen vacancy distribution increases with yttria content and temperature.

The first part of this article concerns the thermodynamics of point defects. In the traditional analysis of reactions in which point defects are involved, point defects are assumed to be ideally diluted, which leads to familiar mass‐action‐type equations. In this article, situations in which deviations from ideal mass‐action‐type behavior occur are investigated by evaluating the influence of defect interactions on the chemical potentials of point defects. Expressions for chemical potentials are derived for the case of weak interactions between neighboring defects. Strong repelling interactions between neighboring defects are discussed using the concept of excluded configurations, and strong attractive interactions are analyzed by introducing clusters. The chemical potential of electrons occupying energy states in an electron band also is analyzed as a function of bandwidth and electron occupation number. An expression for the chemical potential of electrons in partially filled bands is derived, which incorporates the average density of states at the Fermi level. Also discussed is the relationship between formation energies and entropies of defects in oxides and the measurable energy and entropy part of the oxygen chemical potential. The second part of this article concerns the transport of ionic and electronic defects in oxides. Within the framework of irreversible thermodynamics, a formalism is presented that allows the description of the general case in which ambipolar diffusion of ions and electrons in oxides is governed by contributions of several ionic and electronic point defects. The formalism allows the handling of defect association, defect interactions, and coupling of the overall ionic and electronic fluxes. The origin of the coupling and its influence on the net oxygen transport and electric current density is investigated.

The chemical composition of dense ceramics of erbia-stabilized d-Bi2O3 was analyzed by Auger electron spectroscopy (AES) depth profiling using Ar+ ion sputtering. The relative sensitivity factors (rsf) and sputter rates of bismuth and erbium in this material have been determined by electron probe microanalysis (EPMA) and chemical analysis. These results, supplemented by data from angle resolved X-ray photoelectron spectroscopy (ARXPS), shows a bismuth enrichment at the surface. Evidence has been found for reduction of the bismuth-oxide at the outermost part of the surface layer.

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Appreciable oxygen permeabilityat elevated temperatures (650–850°C) allows the well‐known high‐temperature superconductor YBa2Cu3O6+δto be used as an oxygen separation membrane. Permeation of air through a YBa2Cu3O6+δdisk 1.2 mm thick gave an O2stream in which N2was barely detectable by gas chromatography. This technology may have potential applications in high‐temperature oxygen‐based industrial processes.

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The stabilizing and destabilizing mechanism in the action of acetylacetone on zirconium propoxide precursors is revealed; the nature of heteroleptic intermediates provides an explanation.

The stabilizing and destabilizing mechanism in the action of acetylacetone on zirconium propoxide precursors is revealed; the nature of heteroleptic intermediates provides an explanation.

The oxygen non-stoichiometry was determined by coulometric titration for the perovskite oxides La0.2Sr0.8FeO3 − δand La0.2Sr0.8Fe0.8B0.2O3 − δ(B = Ti4 +and Ta5 +) in the temperature range 600 °C ⩽ T⩽ 900 °C and the oxygen partial pressure range: 1·10−15≤pO2≤0.209atm. The non-stoichiometry (δ) is observed to decrease with B-site substitution of Fe. The data can be well fitted with simple defect chemistry models. At low oxygen non-stoichiometry all compositions show a deviation from a localized electrons defect model. The standard and partial molar thermodynamic quantities were obtained and a gradual transition from localized to itinerant electrons with decreasing non-stoichiometry is proposed from the δ-dependency of the configurational entropy. The absolute value of the enthalpy of oxidation decreases upon B-site substitution of Fe proposing a decreased thermodynamic stability for the substituted materials. The electrical conductivity was measured at T= 900 °C in the oxygen partial pressure range: 1·10−17≤pO2≤0.209atm. The electrical conductivity and charge carrier mobility decrease upon 20% substitution of Fe roughly by a factor of 2, but do not show a significant dependence on the nature of the B-site dopant.

The cover picture shows the use of an asymmetric hybrid organic–inorganic membrane in a zero‐emission power plant based on the pre‐combustion CO2capture scheme. In their communication on page 1375, H. Qi, H. J. M. Bouwmeester and co‐workers describe the preparation and extraordinary performance of a sol–gel‐ derived microporous ethylene‐bridged silsesquioxane membrane onto a multilayer support for enhanced CO2separation. The membrane combines superior hydrothermal stability with excellent permselectivities.

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