879 research outputs found
Anode Fabrication for Solid Oxide Fuel Cells: Electroless and Electrodeposition of Nickel and Silver into Doped Ceria Scaffolds
© 2016 The Authors.A novel fabrication method using electroless and electrodeposited Ni/Ag/GDC for SOFC anodes is presented. First a porous Ce0.9Gd0.1O2-x (GDC) scaffold was deposited on a YSZ electrolyte by screen printing and sintering. The scaffold was then metallized with silver using Tollens reaction, followed by electrodeposition of nickel from a Watts bath. The electrodes (Ni/Ag/GDC) were tested in both symmetrical and fuel cell configurations. The microstructures of the Ni/Ag/GDC anodes were analyzed using scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDX). Nano-particles of Ni formed in the porous GDC scaffold provided triple phase boundaries (TPB). The electronic conductivity of the Ni/Ag/GDC (3.5/24.7/71.8 vol%) electrode was good even at relatively low Ni volume fractions. The electrochemical performance was examined in different concentrations of humidified hydrogen (3% H2O) and over a range of temperatures (600-750 °C). The total area specific resistance (ASR) of the anode at 750 °C in humidified 97 vol% H2 was 1.12 Ω cm2, with low-frequency polarization (R-l) as the largest contributor. The electrodes were successfully integrated into a fuel cell and operated in both H2 and syngas
Additive manufacturing for solid oxide cell electrode fabrication
© The Electrochemical Society.Additive manufacturing can potentially offer a highly-defined electrode microstructure, as well as fast and reproducible electrode fabrication. Selective laser sintering is an additive manufacturing technique in which three-dimensional structures are created by bonding subsequent layers of powder using a laser. Although selective laser sintering can be applied to a wide range of materials, including metals and ceramics, the scientific and technical aspects of the manufacturing parameters and their impact on microstructural evolution during the process are not well understood. In the present study, a novel approach for electrode fabrication using selective laser sintering was evaluated by conducting a proof of concept study. A Ni-patterned fuel electrode was laser sintered on an yttria-stabilized zirconia substrate. The optimization process of laser parameters (laser sintering rate and laser power) and the electrochemical results of a full cell with a laser sintered electrode are presented. The challenges and prospects of using selective laser sintering for solid oxide cell fabrication are discussed
Dzyaloshinsky-Moriya interaction in vesignieite: A route to freezing in a quantum kagome antiferromagnet
We report an electron spin resonance investigation of the geometrically
frustrated spin-1/2 kagome antiferromagnet vesignieite,
BaCuVO(OH). Analysis of the line widths and line shifts
indicates the dominance of in-plane Dzyaloshinsky-Moriya anisotropy that is
proposed to suppress strongly quantum spin fluctuations and thus to promote
long-range ordering rather than a spin-liquid state. We also evidence an
enhanced spin-phonon contribution that might originate from a lattice
instability and discuss the origin of a low-temperature mismatch between
intrinsic and bulk susceptibility in terms of local inhomogeneity
Haydeeite: a spin-1/2 kagome ferromagnet
The mineral haydeeite, alpha-MgCu3(OD)6Cl2, is a S=1/2 kagome ferromagnet
that displays long-range magnetic order below TC=4.2 K with a strongly reduced
moment. Our inelastic neutron scattering data show clear spin-wave excitations
that are well described by a Heisenberg Hamiltonian with ferromagnetic
nearest-neighbor exchange J1=-38 K and antiferromagnetic exchange Jd=+11 K
across the hexagons of the kagome lattice. These values place haydeeite very
close to the quantum phase transition between ferromagnetic order and
non-coplanar twelve-sublattice cuboc2 antiferromagnetic order. Diffuse dynamic
short-range ferromagnetic correlations observed above TC persist well into the
ferromagnetically ordered phase with a behavior distinct from critical
scattering
The effect of Mg location on Co-Mg-Ru/γ-Al2O3 Fischer–Tropsch catalysts
© 2016 The Author(s) Published by the Royal Society. All rights reserved.The effectiveness of Mg as a promoter of Co-Ru/γ-Al2O3 Fischer-Tropsch catalysts depends on how and when the Mg is added. When the Mg is impregnated into the support before the Co and Ru addition, some Mg is incorporated into the support in the form of MgxAl2O3+x if the material is calcined at 550°C or 800°C after the impregnation, while the remainder is present as amorphous MgO/MgCO3 phases. After subsequent Co-Ru impregnation MgxCo3-xO4 is formed which decomposes on reduction, leading to Co(0) particles intimately mixed with Mg, as shown by high-resolution transmission electron microscopy. The process of impregnating Co into an Mg-modified support results in dissolution of the amorphous Mg, and it is this Mg which is then incorporated into MgxCo3-xO4. Acid washing or higher temperature calcination after Mg impregnation can remove most of this amorphous Mg, resulting in lower values of x in MgxCo3-xO4. Catalytic testing of these materials reveals that Mg incorporation into the Co oxide phase is severely detrimental to the site-Time yield, while Mg incorporation into the support may provide some enhancement of activity at high temperature
Vesignieite: a kagome antiferromagnet with dominant third-neighbor exchange
The spin- kagome antiferromagnet is an archetypal frustrated
system predicted to host a variety of exotic magnetic states. We show using
neutron scattering measurements that deuterated vesignieite
BaCuVO(OD), a fully stoichiometric kagome
magnet with 1% lattice distortion, orders magnetically at
K into a multi-k coplanar variant of the predicted triple-k
octahedral structure. We find this structure is stabilized by a dominant
antiferromagnetic 3-neighbor exchange with minor
1- or 2--neighbour exchange. The spin-wave
spectrum is well described by a -only model including a tiny symmetric
exchange anisotropy
Fabrication and characterisation of nanoscale Ni-CGO electrode from nanocomposite powders
Incorporating nanoparticles into SOC electrode is a viable method to improve the electrochemical performance. In this work, nanoparticles of NiO and gadolinia-doped ceria (CGO) approximately 10 nm in diameter fabricated using a continuous hydrothermal flow synthesis are made into nano-structured SOC fuel electrodes via mixing and co-sintering. Both the Ni and CGO are of 50-100 nm in diameter in the final electrode. FIB-SEM 3-D tomography is carried out on the nanoscale Ni-CGO electrode which has been aged for 70 h, showing a high active triple phase boundary density of 3 µm-2 and a high active double phase boundary density of 2 µm-1. The total polarisation resistance of the electrode is stable at 0.20 Ω cm2 under open circuit conditions at 800 °C annealing in humidified 5% H2-N2
Suscetibilidade dos estágios imaturos de Trichogramma pretiosum a óleos inseticidas.
O objetivo desse trabalho foi avaliar a suscetibilidade das fases imaturas do parasitoide Trichogramma pretiosum a óleos vegetais e sintéticos utilizados no controle fitossanitário de pragas.Resumo
Ground State and Intrinsic Susceptibility of the Kagome Antiferromagnet Vesignieite as seen by 51V NMR
The intrinsic magnetic susceptibility and local magnetization of the
near-kagome quantum magnet vesignieite, Cu3BaV2O8(OH)2, are presented as
measured using 51V NMR. The NMR line shift gives an accurate measurement of the
intrinsic susceptibility of the kagome sites which closely resembles that of
the quantum spin liquid herbertsmithite [A. Olariu et al. Phys. Rev. Lett. 100,
087202 (2008)]. It is therefore surprising that, at Tc ~ 9 K, a transition to a
heterogeneous ground state is observed. A gradual wipeout of half the NMR
intensity indicates a slowly fluctuating spin liquid component and a detailed
analysis of the linewidth reveals the onset of static magnetism at the
remaining half of the sites. It is proposed that this transition and unusual
ground state originate from a nearby quantum critical point induced by the
Dzyaloshinskii-Moriya interaction.Comment: 5 pages, 4 figure
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