Abstract
Octahedral molecular sieves (OMS) are built of transition metal-oxygen octahedra that delimit sub-nanoscale cavities. Compared to other microporous solids, OMS exhibit larger versatility in ...properties, provided by various redox states and magnetic behaviors of transition metals. Hence, OMS offer opportunities in electrochemical energy harnessing devices, including batteries, electrochemical capacitors and electrochromic systems, provided two conditions are met: fast exchange of ions in the micropores and stability upon exchange. Here we unveil a novel OMS hexagonal polymorph of tungsten oxide called
h’-WO
3
, built of (WO
6
)
6
tunnel cavities.
h’-WO
3
is prepared by a one-step soft chemistry aqueous route leading to the hydrogen bronze
h’-H
0.07
WO
3
. Gentle heating results in
h’-WO
3
with framework retention. The material exhibits an unusual combination of 1-dimensional crystal structure and 2-dimensional nanostructure that enhances and fastens proton (de)insertion for stable electrochromic devices. This discovery paves the way to a new family of mixed valence functional materials with tunable behaviors.
Pure ionic conductors as solid‐state electrolytes are of high interest in electrochemical energy storage and conversion devices. They systematically involve only one ion as the charge carrier. The ...association of two mobile ionic species, one positively and the other negatively charged, in a specific network should strongly influence the total ion conduction. Nb5+‐ (4d0) and Ti4+‐based (3d0) derived‐perovskite frameworks containing Na+ and O2− as mobile species are investigated as mixed ion conductors by electrochemical impedance spectroscopy. The design of Na+ blocking layers via sandwiched pellet sintered by spark plasma sintering at high temperatures leads to quantified transport number of both ionic charge carriers tNa+ and tO2−. In the 350–700 °C temperature range, ionic conductivity can be tuned from major Na+ contribution (tNa+ = 88%) for NaNbO3 to pure O2− transport in NaNb0.9Ti0.1O2.95 phase. Such a Ti‐substitution is accompanied with a ≈100‐fold increase in the oxygen conductivity, approaching the best values for pure oxygen conductors in this temperature range. Besides the demonstration of tunable mixed ion conduction with quantifiable cationic and anionic contributions in a single solid‐state structure, a strategy is established from structural analysis to develop other architectures with improved mixed ionic conductivity.
The transport numbers of sodium cations and oxygen anions are quantified in niobate pervoskites via an original method using sandwiched pellets with solid Na+‐blocking/O‐conducting layers. Above 350 °C, charge carriers switch from major Na+/minor O2− for NaNbO3 to exclusive O2− for NaNb0.9Ti0.1O2.95. This first evidence of mixed‐ion Na+/O2− underlies a novel strategy toward improved ionic conductivity in perovskite‐derived structures.
Abstract
Nanoshells made of a silica core and a gold shell possess an optical response that is sensitive to nanometer-scale variations in shell thickness. The exponential red shift of the plasmon ...resonance with decreasing shell thickness makes ultrathin nanoshells (less than 10 nm) particularly interesting for broad and tuneable ranges of optical properties. Nanoshells are generally synthesised by coating gold onto seed-covered silica particles, producing continuous shells with a lower limit of 15 nm, due to an inhomogeneous droplet formation on the silica surface during the seed regrowth. In this paper, we investigate the effects of three variations of the synthesis protocol to favour ultrathin nanoshells: seed density, polymer additives and microwave treatment. We first maximised gold seed density around the silica core, but surprisingly its effect is limited. However, we found that the addition of polyvinylpyrrolidone during the shell synthesis leads to higher homogeneity and a thinner shell and that a post-synthetic thermal treatment using microwaves can further smooth the particle surface. This study brings new insights into the synthesis of metallic nanoshells, pushing the limits of ultrathin shell synthesis.
All-solid-state-batteries (ASSBs) are one of the most promising post-lithium-ion technologies that can increase the specific energy density and safety of secondary lithium batteries. Solid sulfide ...electrolytes are considered as promising candidates to be used in ASSBs owing to high ionic conductivities. In particular, solid electrolytes in the Li2S − P2S5 binary system have attracted considerable attention as they are composed of low-cost elements and they provide ionic conductivity values comparable to those of liquid electrolytes (>10−4 Scm−1). In this review, the structural properties and synthesis methods of materials in the binary system are summarized. Distinctions in local structures and Li-ion conduction properties between glassy, glass-ceramic, and crystalline materials are highlighted. Possible mechanisms are proposed for the fast ionic conduction observed in glass-ceramics. Important parameters of each synthesis method are suggested and the relationships between structure, synthesis and material properties are discussed. The goals of this review are to provide greater understanding of the state-of-the-art in the field, and to point out the overlooked aspects for application.
•Structural properties within the Li2S-P2S5 system.•Possible mechanisms are proposed for the fast ionic conduction observed in glass-ceramics. State-of-the-art in the field.•Overlooked aspects for application.
The objectives of the work presented in this article are two folds. First it presents computed properties of the semiconductor BiCuOS at the HSE06+spin–orbit coupling level and these properties are ...interpreted from the composition of the material point of view and are analyzed from a photovoltaic perspective. The calculated properties (E g = 1.22 eV, εr = 36.2, m e * = 0.42, m h * = 0.33, E b = 2 meV) illustrate that BiCuOS is a promising material for photovoltaic application. The second objective is to presents a multiscale approach whose objective is to simulate photovoltaic macroscopic characteristics (J sc, V oc, FF, ...) from microscopic properties computed at the DFT level. The approach is first tested in the CuInS2 solar cell, that has several similarities with BiCuOS, allowing to determine the strengths and limits of this approach. Then, this protocol is applied to BiCuOS solar cells in order to determine the best n-type semiconductor to put in contact with BiCuOS to achieve high photoconversion efficiencies. The results allow to dress the list of the drawbacks that must be overcome to use this material for photovoltaic application. Beyond BiCuOS, this protocol can be used by the community wanting to use modeling to design and characterize new semiconductors beyond the bandgap calculation.
Thermal degradation of blue phosphor BAM:Eu2+ under air is investigated using XPS, XRD, EPR and photoluminescence (PL) in order to analyze the loss of intensity in terms of modifications of the ...dopant distribution in the crystal cell and between crystal bulk and surface. This study reveals the key role played by oxidation-driven 2D diffusion of europium and barium, that results in important concentration gradients and makes degradation strongly dependent on both microstructure and cooling speed. Also based upon cation mobility, a possible regeneration effect is evidenced at moderate temperature. Flux treatments, known to increase the intensity of photoluminescence, also appear to reduce thermal degradation by lowering specific surface; they also enhance the regeneration process by forming extended single-crystal domains conducive to cation diffusion.
•High stake but still controversial thermal degradation of blue phosphor BAM:Eu2+ is explained.•A new multi-scale structural model is proposed, based on a wide spectrum of analytical methods.•Long-range transport of Ba2+ and Eu2+/Eu3+ ions and concentration gradients are evidenced.•Also based upon cation diffusion, an inedite regeneration process is proposed.
A new class of cost‐efficient n‐type thermoelectric sulfides with a layered structure is reported, namely MnBi4S7 and FeBi4S7. Theoretical calculations combined with synchrotron X‐ray/neutron ...diffraction analyses reveal the origin of their electronic and thermal properties. The complex low‐symmetry monoclinic crystal structure generates an electronic band structure with a mixture of heavy and light bands near the conduction band edge, as well as vibrational properties favorable for high thermoelectric performance. The low thermal conductivity can be attributed to the complex layered crystal structure and to the existence of the lone pair of electrons in Bi3+. This feature combined with the relatively high power factor lead to a figure of merit as high as 0.21 (700 K) in undoped MnBi4S7, making this material a promising n‐type candidate for low‐ and intermediate‐temperature thermoelectric applications.
Ultralow thermal conductivity is reported in new cost‐efficient n‐type layered XBi4S7 (X = Mn, Fe) thermoelectric materials. The complex layered crystal structure, exhibiting a multiband electronic structure and ultralow thermal conductivity, favors high thermoelectric performance.
In this work, we present a comprehensive study dealing with the modeling of the conversion process occurring in a redox flow cell. Experiments are carried out on an original millifluidic flow battery ...with ferrocyanide and iodide as electrolytes. A simulation model supports the experimental data. In flow, intensity recovery is limited by the mass transfer. Thanks to diffusion, at low Peclet, the conversion is complete. On the contrary, at high Peclet, the convection prevents the diffusion of species and induces a conversion drop. A quantitative agreement is found between theoretic model and experiment both on current and on power curves. The originality of our work is to take into account the kinetics of the redox reaction at the electrodes. We evidence a new regime where the current intensity is constant as a function of the Peclet number. The maximal recovered power is obtained at a given flow rate and not at very high flow rate. This work paves the road for the optimization of the conversion process and for the measurements of the thermodynamic parameters involved in the redox process such as kinetic parameters at the electrodes.
Abstract
Metallic nanowire percolating networks are one of the promising alternatives to conventional transparent conducting electrodes. Among the conductive metals, copper appears as a relevant ...alternative to develop electrodes in a more sustainable and economical way (abundance of the supplies, geo-political risks regarding the supplies, environmental impact, and cost). However, Cu nanowires suffer from high instability in air, and one of the ways to increase stability as well as to boost properties related to transparent electrodes is to combine the Cu with another metal, resulting in bimetallic nanowires. Even though the field of fabrication of nanoalloys has been advancing at a rapid pace in the last two decades, binary nanowires are difficult to produce due to a wide range of parameters that must be aligned in regard to metals that are being combined, such as surface energy of the bulk metal, atomic radii, crystal lattice matching, redox potentials, etc. In this review, we present the current research landscape in making Cu-based bimetallic nanowires for the development of metal nanowire networks with high oxidation resistance. This analysis allows identifying the most promising bimetallic materials for obtaining highly efficient, robust, and cost-effective electrodes.
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