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Abstract: Composites of ion and electron conducting phases allow for interfacial storage of a neutral component via space charge effects. The present contribution considers the rate of transport‐controlled incorporation and excorporation in such artificial mixed conductors. The upper limit of the relaxation time is determined by interfacial job‐sharing diffusion which is analyzed in greater detail. In general cases bulk phases assist by migration processes (dual phase transport). For more complex morphological situations, the considerations are complemented by numerical calculations. Thus the treatment also offers a pertinent approach with respect to the kinetics of solid state supercapacitors. Selected experimental results are included in the discussion. [ABSTRACT FROM AUTHOR]

Oxygen vacancies play a role in various proposed degradation mechanisms of Pb(ZrxTi1-x)O3 (PZT)-based applications. Hence, 18O tracer diffusion experiments investigated by time-of-flight-secondary ion mass spectrometry were used in order to evaluate oxygen diffusion in donor-doped polycrystalline PZT. The PZT shows fast grain-boundary diffusion for annealing temperatures around 650°C with a strong temperature dependency. 18O intensity images clearly coincide with maps of grain boundaries. Within individual grains, local diffusion profiles could be measured and revealed bulk diffusion as well as evidence of a near-surface space-charge layer. The bulk and grain-boundary diffusion coefficients for the samples annealed at 650°C could be calculated with respect to type B diffusion kinetics. Comparison with electrical measurements showed that oxide ion conduction in grain boundaries significantly contributes to the total conductivity of donor-doped PZT. [ABSTRACT FROM AUTHOR]

Detailed insight into electrochemical reaction mechanisms and rate limiting steps is crucial for targeted optimization of solid oxide fuel cell (SOFC) electrodes, especially for new materials and processing techniques, such as Ni/Gd-doped ceria (GDC) cermet anodes in metal-supported cells. Here, we present a comprehensive model that describes the impedance of porous cermet electrodes according to a transmission line circuit. We exemplify the validity of the model on electrolyte-supported symmetrical model cells with two equal Ni/Ce0.9Gd0.1O1.95-δ anodes. These anodes exhibit a remarkably low polarization resistance of less than 0.1 Ωcm2 at 750 °C and OCV, and metal-supported cells with equally prepared anodes achieve excellent power density of >2 W/cm2 at 700 °C. With the transmission line impedance model, it is possible to separate and quantify the individual contributions to the polarization resistance, such as oxygen ion transport across the YSZ-GDC interface, ionic conductivity within the porous anode, oxygen exchange at the GDC surface and gas phase diffusion. Furthermore, we show that the fitted parameters consistently scale with variation of electrode geometry, temperature and atmosphere. Since the fitted parameters are representative for materials properties, we can also relate our results to model studies on the ion conductivity, oxygen stoichiometry and surface catalytic properties of Gd-doped ceria and obtain very good quantitative agreement. With this detailed insight into reaction mechanisms, we can explain the excellent performance of the anode as a combination of materials properties of GDC and the unusual microstructure that is a consequence of the reductive sintering procedure, which is required for anodes in metal-supported cells. [ABSTRACT FROM AUTHOR]

Abstract: The oxygen exchange and diffusion properties of La0.6Sr0.4CoO3−δ thin films on yttria stabilized zirconia were analyzed by impedance spectroscopy and 18O tracer experiments. The investigations were performed on the same thin film samples and at the same temperature (400°C) in order to get complementary information by the two methods. Electrochemical impedance spectroscopy can reveal resistive and capacitive contributions of such systems, but an exact interpretation of the spectra of complex oxide electrodes is often difficult from impedance data alone. It is shown that additional isotope exchange depth profiling can significantly help interpreting impedance spectra by giving reliable information on the individual contribution and exact location of resistances (surface, electrode bulk, interface). The measurements also allowed quantitative comparison of electrode polarization resistances obtained by different methods. [Copyright &y& Elsevier]

Oxide interfaces have attracted a huge amount of interest in recent years due to their novel functionalities that are not possible in bulk. Here we employ atomistic simulation techniques to study the defect properties and oxygen ion migration energy in bulk SrTiO 3 , LaCrO 3 and SrTiO 3 –LaCrO 3 interface. The SrO and La 2 O 3 "Schottky-like" defects are found to be the most favourable intrinsic defects in their respective bulk structures and also at interface layers. While defect energies calculated at interface layers are not significantly changed compared to that calculated in the bulk LaCrO 3 , significant changes are noted in Schottky defects and oxygen Frenkel between bulk SrTiO 3 and the interface. The activation energies for the oxygen ion diffusion in bulk SrTiO 3 and LaCrO 3 are calculated to be 0.64 eV and 0.53 eV, respectively, suggesting that both materials will present favourable diffusion pathways. In general, there is a reduction in the activation energies of oxygen ion migration at the interface compared to bulk structures. In particular, in the Cr layer, activation energy is calculated to be 0.36 eV implying that interface plays an important role in the oxygen ion migration and therefore such an interface is of interest for use in advanced electrochemical devices. • Defect processes and O-transport in SrTiO 3 -LaCrO 3 are studied theoretically. • The energetically favourable defect type is partial Schottky. • Oxygen ion migration is low in SrTiO 3 and LaCrO 3 fast. • SrTiO 3 -LaCrO 3 interface enhances ion conductivity. [ABSTRACT FROM AUTHOR]