Tobias Scherb

Synthesis and Characterization of Nonsubstituted and Substituted Proton-Conducting La6–xWO12–y

Mixed proton-electron conductors (MPEC) can be used as gas separation membranes to extract hydrogen from a gas stream, for example, in a power plant. From the different MPEC, the ceramic material lanthanum tungstate presents an important mixed protonic-electronic conductivity. Lanthanum tungstate La(6-x)WO(12-y) (with y = 1.5x + δ and x = 0.5-0.8) compounds were prepared with La/W ratios between 4.8 and 6.0 and sintered at temperatures between 1300 and 1500 °C in order to study the dependence of the single-phase formation region on the La/W ratio and temperature. Furthermore, compounds substituted in the La or W position were prepared. Ce, Nd, Tb, and Y were used for partial substitution at the La site, while Ir, Re, and Mo were applied for W substitution. All substituents were applied in different concentrations. The electrical conductivity of nonsubstituted La(6-x)WO(12-y) and for all substituted La(6-x)WO(12-y) compounds was measured in the temperature range of 400-900 °C in wet (2.5% H2O) and dry mixtures of 4% H2 in Ar. The greatest improvement in the electrical characteristics was found in the case of 20 mol % substitution with both Re and Mo. After treatment in 100% H2 at 800 °C, the compounds remained unchanged as confirmed with XRD, Raman, and SEM.

On the structural integrity and electrochemical activity of a 0.5Li2MnO3·0.5LiCoO2 cathode material for lithium-ion batteries

Structural changes in a 0.5Li2MnO3·0.5LiCoO2 cathode material were investigated by X-ray absorption spectroscopy. It is observed that both Li2MnO3 and LiCoO2 components of the material exist as separate domains, however, with some exchange of transition metal (TM) ions in their slab layers. A large irreversible capacity observed during activation of the material in the 1st cycle can be attributed to an irreversible oxygen release from Li2MnO3 domains during lithium extraction. The average valence state of manganese ions remains unchanged at 4+ during charge and discharge. In the absence of conventional redox processes, lithium extraction/reinsertion from/into Li2MnO3 domains occurs with the participation of oxygen anions in redox reactions and most likely involves the ion-exchange process. In contrast, lithium deintercalation/intercalation from/into LiCoO2 domains occurs topotactically, involving a conventional Co3+/Co4+ redox reaction. The presence of Li2MnO3 domains and their unusual participation in electrochemical processes enable LiCoO2 domains of the material to sustain a higher cut-off voltage without undergoing irreversible structural changes.

Nanoscale order in the frustrated mixed conductor La5.6WO12-δ

Helmholtz-Zentrum Berlin für Materialien und Energie (HZB), Hahn-Meitner-Platz 1, 14109 Berlin, Germany, European Synchrotron Radiation Facility (ESRF), 6 rue Jules Horowitz, BP 220, 38043 Grenoble Cedex 9, France, Freie Universität Berlin, Malteserstrasse 74-100, 12249 Berlin, Germany, Bundesanstalt für Materialforschung und -prüfung (BAM), Unter den Eichen 87, 12205 Berlin, Germany, European Spallation Source ESS AB, Box 176, 22100 Lund, Sweden, Instituto de Tecnologı́a Quı́mica (UPV-CSIC), Avenida los Naranjos s/n, 46022 Valencia, Spain, Forschungszentrum Jülich GmbH (FZJ), 52425 Jülich, Germany, and Technische Universität Berlin, Hardenbergstrasse 36, 10623 Berlin, Germany. *Correspondence e-mail: tobias.scherb@helmholtz-berlin.de