This site makes use of cookies necessary for the operation and useful for the purposes described in the cookie policy. If you want to learn more, see the cookie policy. By closing this banner, scrolling this page, clicking on a link or continuing navigation in any other way, you consent to the use of cookies.
Using high resolution computed tomography (CT) the change of the morphometric parameters in depth of electrodes for lithium ion batteries with aging has been examined. Commercially available 2 Ah Li-ion cells were continuously cycled to different state of health (SOH). The cathodes were subsequently analyzed using CT with voxel size resolution of about 400 nm. For a quantitative analysis binarized images were evaluated and various properties such as the size distribution of active particles analyzed. Using this technique a decrease in the average particle size and an increase in number of particles of LiCoO2 with decreasing SOH of the battery is confirmed experimentally for the first time.
Polymer grafting from graphitic carbon materials has been explored for several decades. Currently existing methods mostly employ harsh chemical treatment to generate defect site in graphitic carbon plane, which are used as active site for polymerization of precursors. Unfortunately, the treatment cause serious degradation of chemical structure and material properties. Here, we present a straightforward route for growth of polyaniline chain from nitrogen (N)-sites of carbon nanotubes. N site in the CNT wall initiates the polymerization of aniline monomer, which generates seamless hybrids composed of polyaniline directly grafted onto the CNT walls. The synthesized hybrids show excellent synergistic electrochemical performance, and are employed for electrodes of pseudo-capacitor. This approach offers an efficient way to obtain hybrid system consisting of conducting polymers directly grafted from graphitic dopant sites.
Use of spark plasma sintering (SPS) allows improving thermoelectric figure of merit Z of bulk nanothermoelectrics but required parameters of SPS process for achievement of best Z can be defined only empirically.
In the present study the finite elements method for investigation of electric and thermal processes which occur in volume and on boundaries of sintering particles is applied. As a geometrical model a structural cell of a sintered sample, containing contact “a truncated cone - a plate” has been chosen. Temperature distributions in the volume of a sample depending on amplitude, on-off time ratio and duration of impact of the electric current has been obtained for solid solution based on bismuth telluride using the energy balance equation and the equation of electric current continuity. Under certain conditions nonlinear and nonlocal processes start to arise.
The calculated temperature distributions at different sintering conditions were comparing with empirically defined experimental parameters that lead to improved value of Z. The comparison allows formulating recommendations to achieve best conditions of SPS process for increase of Z. The present method can be used for management of SPS fabrication process for different application, not only for thermoelectrics.
Regarding catalytic and plasmonic properties of gold nanoparticles (NPs), the novel area of research on photocatalytic gold properties has been recently started. In contrast with catalytically active gold NPs, where nano-sized gold is recommended, our results showed that polydispersity of deposited gold NPs on semiconducting support was beneficial for photocatalytic activity under visible light irradiation. It is thought that wide size/shape distribution of gold NPs, and thus the ability of absorption of light in a wide wavelengths range is responsible for the high level of photoactivity. Though desirable absorption properties of plasmonic photocatalysts can be easily obtained by preparation of nanoparticles of different sizes and shapes, their photocatalytic activities under visible light irradiation are still low and should be enanced. The improvement of photocatalytic activities under visible light irradiation was achieved by enlargement of interfacial contact between titania and NPs of noble metals, extension of photoabsorption ranges (by preparation of NPs of various sizes and shapes or composed of two kinds of noble metals), and by deposition of noble metals NPs on faceted titania, i.e., octahedral (OAPs) and decahedral (DAPs). Plasmonic photocatalysts composed of titania and NPs of silver, gold or copper showed also high antiseptic properties under visible light irradiation, due to possible synergism of antiseptic properties of noble metals and photodisinfection properties of photocatalyst, since reactive oxygen species or photogenerated holes are formed on the surface of irradiated semiconductor.
A co-catalyst was synthesized by photochemically depositing Pd nanoparticles onto TiO2 nanopowder support in a one-pot synthesis procedure. The Pd nanoparticles exhibited localised surface plasmon resonance observed using UV-VIS which increased the absorption cross-section of the co-catalyst system into the visible as well as UV regions of the spectrum. This was found to have a significant contribution to the photocatalytic activity of the catalyst in dye degradation experiments. The size, morphology and distribution of the Pd nanoparticles were determined by TEM, while the chemical state and amount of Pd deposited were analysed via XPS and ICP respectively.
We use BaTiO3 as a model photocatalyst to investigate the effect of ferroelectricity on catalytic activity against photocatalytic decolourisation of Acid Black 1. We find that there is a strong relationship between the degree of ferroelectric nature of the BaTiO3 and the catalytic activity. When Ag is photodeposited onto BaTiO3 to produce a modified BaTiO3, the higher tetragonal material content shows the highest photocatalytic efficiency even though there is a reduced surface area due to heat treatment. This change in the performance of the catalyst is associated with improvements in charge carrier separation due to the internal space charge layer formed in a ferroelectric due to the internal dipole.
We show that we have developed a hydrothermal process that produces a high surface area TiO2 on glass fibre supports. The as produced titania shows good photocatalytic activity against a standard commercial dye – Rhodamine B– giving full decolourisation within 3 hours under UV and visible light irradiation. The samples are mechanically robust and can act as a photocatalytic filter for waste streams and pollutants. In addition to testing the standard titania we also photochemically deposit nanostructures of Pd. These hybrid catalysts show enhanced decolourisation by an order of magnitude over the native titania systems. This enhanced performance is due to the increased energy harvesting of the hybrid system through a visible light plasmon interaction and the direct injection of electrons from the noble metal into the adsorbed dye molecules. There is a clear relationship between the absorbed light and photochemical reactivity of the system which is further explained in terms of electron hole generation and separation and plasmonic interaction. In summary, we have generated a high performance catalyst that is produced on a bulk commodity substrate with enhanced activity due to control of the surface plasmon and direct band gap transition of electron hole pairs in the semi-conductor.
The influence of super high frequency (SHF) circular magnetic field on magnetization reversal in the Co-rich glass covered microwire has been investigated. The study has been performed by magneto-optical Kerr effect (MOKE) technique. It was found that the presence of the SHF field causes the change of the re-magnetization mechanism – the rotation of the magnetization is observed instead of domain walls motion. Also the hysteresis loop has an asymmetric shape that confirms the co-existence of the stable and meta-stable helical magnetic states in the surface of microwires.
The paper considers the effects of compacting pressure and the working parameters (maximum flux density, excitation frequency) on power loss dissipated in a soft magnetic composite core. The effects may be efficiently described with simple power laws . The description has been verified using commercial SMC cores. The proposed dependencies are in a good agreement with experiment.
Magnetocaloric materials with a Curie temperature near room temperature are of interest for application in high-efficiency solid state cooling. There are several promising families of materials including the LaFe13-xSix system which offers large magnetocaloric entropy change, low magnetic and thermal hysteresis, and tunability of the metamagnetic transition by introduction of interstitial hydrogen or partial substitution on the La or Fe sites. There is a large amount of literature on the properties and mechanism of the magnetocaloric effect in this material system, and more recently our group and several other groups have discussed the origins of the dynamics of the metamagnetic transition and its relation to magnetic hysteresis. Nevertheless, although extremely informative in other systems, there has been little spatially resolved information concerning the nature of the magnetic transition in this system. Here we use scanning Hall probe imaging to study LaFe13-xSix polycrystalline samples with x=1.2 prepared by induction melting to resolved the local static and dynamic magnetic properties. We find that the local properties of the magnetic transition are governed by chemical inhomogeneity rather that demagnetization effects associated with sample geometry.
One of the most surprising and significant advances in the study of the photosynthetic light- harvesting process is the discovery that the electronic energy transfer (ET) might involve long-lived electronic coherences, also at physiologically relevant conditions. This means that the transfer of energy among different chromophores does not follow the expected classical incoherent hopping mechanism, but that quantum-mechanical laws can steer the migration of energy. The implications of such quantum transport regime, although currently under debate, might have a tremendous impact in our way to think about natural and artificial light-harvesting and suggest new directions for the development of artificial devices for the efficient capture and re-use of solar energy. Central to these discoveries has been the development of new ultrafast spectroscopic techniques, in particular two-dimensional electronic spectroscopy, which is now the primary tool to obtain clear and definitive experimental proof of such effects.
Different nanocomposite materials consisting of semiconducting CdSe nanocrystals (NCs) and a low band gap copolymer poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b:3.4- b’]dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT) were prepared, morphologically characterized, and tested in hybrid solar cells. In addition, a PCPDTBT-based rod-coil diblock copolymer was synthesized through a grafting-onto approach and a preliminary evaluation of the morphology of the hybrid nanocomposites with CdSe NCs was performed.
Address
Links
Information