Synthesis and Study of a Ce-Doped La/Sr Titanate for Solid Oxide Fuel Cell Anode Operating Directly on Methane

6 Perillat-Merceroz, Cedric Gauthier, Gilles Roussel, Pascal Huve, Marielle Gelin, Patrick Vannier, Rose-NoelleThe possibility to introduce cerium in the perovskite-type titanate with formula La0.33Sr0.67TiO3+delta (LST) was investigated. Pure-phased La0.23Ce0.1Sr0.67TiO3+delta (LCST) was only obtained by synthesis at high temperature in reducing (diluted hydrogen) atmosphere. The material exhibits the same orthorhombic symmetry with Immm space group as LST and nearly the same cell volume. When exposed to oxidizing atmosphere at 1200 degrees C, Ti3+ and Ce3+ oxidation leads to the decomposition of LCST and the growth of several nanoscaled Ce-rich phases, as highlighted by backscattered electron microscopy. Shifting the gas back to a reducing atmosphere, but at lower temperature, only involves partial reversibility, ensuring the presence of nanoparticles of (electro)catalytically active phase within an electronically conducting n-type network. The catalytic tests in methane steam reforming at 900 degrees C (CH4/H2O = 10/1) show that the properties of the partially decomposed phase are greatly improved, what could make it a promising anode material for SOFC operating on slightly wet methane

Pure and Mn-doped La4SrTi5O17 layered perovskite as potential solid oxide fuel cell material: Structure and anodic performance

SSCI-VIDE+ATARI+PGEInternational audiencePure and 5% Mn doped layered perovskites La4SrTi5O17, members of the La4Srn-4(Ti,Mn)(n)O3n+2 series with n = 5, have been synthesized and investigated as anode materials for Solid Oxide Fuel Cells. The use of XRD, neutron and electron diffraction techniques allows clarifying some divergences concerning the structural characterization within the family, not only in air but also in anodic-like N-2/H-2(97/3) atmosphere. The electrical conductivity of both compounds is very low in air but those values increase by two orders of magnitude in diluted hydrogen. The study of catalytic properties for methane steam reforming as well as in-depth analysis of the SOFC anodic behaviour of both materials are described, for which a microstructure optimization of the electrode allows to demonstrate the potential interest of the lamellar materials upon the classical three-dimensional cubic-like LSTs. (C) 2014 Elsevier B.V. All rights reserved

Microstructural investigations and nanoscale ferroelectric properties in lead-free Nd2Ti2O7 thin films grown on SrTiO3 substrates by pulsed laser deposition

The growth conditions required to obtain high-quality layered-perovskite Nd2Ti2O7 thin films with a monoclinic structure on both (100)- and (110)-oriented SrTiO3 substrates by pulsed laser deposition are investigated. To synthesize the expected ferroelectric crystalline phase (and optimize the crystallization), two major critical parameters have to be carefully controlled, i.e. the oxygen pressure during deposition and the substrate temperature. Combining X-ray diffraction and transmission electron microscopy for structural characterizations, a twinned structure with (00l) orientation is evidenced for the films grown on (110)-oriented SrTiO3 while a twinned structure with a (012) orientation slightly tilted from 3.6u with respect to the substrate plane is revealed in the case of (100)-oriented SrTiO3. For growth performed at very low pressure, NdTiO3+delta thin films are obtained while polymorphic non-ferroelectric Nd2Ti2O7 samples with an orthorhombic structure are found at higher pressures. Piezoresponse force microscopy experiments evidence nanoscale ferroelectricity in the layered-perovskite monoclinic Nd2Ti2O7 films deposited on both substrates. Domain switching properties are shown to be more reliable for films grown onto (110)-SrTiO3 substrates, demonstrating these are more suitable as a functional material for applications in the field of micro-/nano-electronics. On the other hand, no ferroelectricity is probed in the polymorphic Nd2Ti2O7 thin films, as expected in a centro-symmetric structure

Plasticity and stress tolerance override local adaptation in the responses of Mediterranean holm oak seedlings to drought and cold

11 pages, figures, and tables statistics.Plant populations of widely distributed species experience a broad range of environmental conditions that can be faced by phenotypic plasticity or ecotypic differentiation and local adaptation. The strategy chosen will determine a population’s ability to respond to climate change. To explore this, we grew Quercus ilex (L.) seedlings from acorns collected at six selected populations from climatically contrasting localities and evaluated their response to drought and late season cold events. Maximum photosynthetic rate (Amax), instantaneous water use efficiency (iWUE), and thermal tolerance to freeze and heat (estimated from chlorophyll fluorescence versus temperature curves) were measured in 5-month-old seedlings in control (no stress), drought (water-stressed), and cold (low suboptimal temperature) conditions. The observed responses were similar for the six populations: drought decreased Amax and increased iWUE, and cold reduced Amax and iWUE. All the seedlings maintained photosynthetic activity under adverse conditions (drought and cold), and rapidly increased their iWUE by closing stomata when exposed to drought. Heat and freeze tolerances were similarly high for seedlings from all the populations, and they were significantly increased by drought and cold, respectively; and were positively related to each other. Differences in seedling performance across populations were primarily induced by maternal effects mediated by seed size and to a lesser extent by idiosyncratic physiologic responses to drought and low temperatures. Tolerance to multiple stresses together with the capacity to physiologically acclimate to heat waves and cold snaps may allow Q. ilex to cope with the increasingly stressful conditions imposed by climate change. Lack of evidence of physiologic seedling adaptation to local climate may reflect opposing selection pressures to complex, multidimensional environmental conditions operating within the distribution range of this species.The authors thank F. Pulido for providing acorns, and E. Palma, E. Beamonte, and S. Matesanz for assistance in the glasshouse. This work was supported by the project ECOCLIM (CGL2007- 66066-C04-02, MEC). TEG and BP hold I3P predoctoral and postdoctoral fellowships, respectively, both awarded by the Spanish Scientific Council (CSIC). J.P.L. held a collaboration fellowship awarded by the Brazilian Scientific Coordination (CAPES).Peer reviewe

The deep-water Peyssonnelia beds from the Balearic islands (Western Mediterranean)

Peyssonnelia bed distribution on continental shelf bottoms of the Balearic Islands (Western Mediterranean) ranges from 40 to 90 m depth. Different species of Peyssonnelia dominate these bottoms and, according to multivariate techniques, two main assemblages have been distinguished: the Peyssonnelia rosa-marina beds and the Peyssonnelia sp. beds, together with some transition samples between Peyssonnelia and maërl beds. Erect red algae are always abundant. Although average yearly irradiance reaching these beds is only 6.4-0.3% of subsurface irradiance, the species richness averages 45 species per sample (1600 cm2) and mean biomass is 2835 g dw. m-2. The high carbonate content of the living algae of these bottoms suggests that they are important contributors to the production of sediments in the Balearic continental shelf.Peer reviewe