Cyclic Voltammetry of C.I. Disperse Orange 62 in an Aqueous Electrolyte.

Disperse dyes are an important group of colorants for dyeing polyester fibers. Approximately 30.000 tons of disperse dyes are released into the waste water annually from spent dyebaths. Therefore, methods for decolorizing such dyes are of general interest. The reductive after-treatment of disperse dyes using reducing agents, such as Na2S2O4, is a widely used process to improve rub fastness through dye reduction. Electrochemical dye reduction could be an alternative process for reductive dye treatment. In this work C.I. Disperse Orange 62 was used as a representative dye to study the direct cathodic reduction of a disperse dye with cyclic voltammetry. As anticipated for dispersed organic matter, relatively low current densities were observed, which strongly depend on the state of dispersion of the dye. The current density was increased by using dispersions prepared through dye precipitation from DMF solution and by the use of N-cetyl-N,N,N,-trimethyl-ammonium bromide as a cationic surfactant. The results demonstrate the successful cathodic reduction of a dispersed organic dye; however, the low solubility of the reaction products in the aqueous electrolyte hinders an efficient cathodic dye reduction.

Multi-Point Flexible Temperature Sensor Array and Thermoelectric Generator Made from Copper-Coated Textiles.

The integration of electrical functionality into flexible textile structures requires the development of new concepts for flexible conductive material. Conductive and flexible thin films can be generated on non-conductive textile materials by electroless metal deposition. By electroless copper deposition on lyocell-type cellulose fabrics, thin conductive layers with a thickness of approximately 260 nm were prepared. The total copper content of a textile fabric was analyzed to be 147 mg per g of fabric, so that the textile character of the material remains unchanged, which includes, for example, the flexibility and bendability. The flexible material could be used to manufacture a thermoelectric sensor array and generator. This approach enables the formation of a sensor textile with a large number of individual sensors and, at the same time, a reduction in the number of electrical connections, since the conductive textile serves as a common conductive line for all sensors. In combination with aluminum, thermoelectric coefficients of 3-4 µV/K were obtained, which are comparable with copper/aluminum foil and bulk material. Thermoelectric generators, consisting of six junctions using the same material combinations, led to electric output voltages of 0.4 mV for both setups at a temperature difference of 71 K. The results demonstrate the potential of electroless deposition for the production of thin-film-coated flexible textiles, and represent a key technology to achieve the direct integration of electrical sensors and conductors in non-conductive material.

Water-based slurries for high-energy LiFePO4 batteries using embroidered current collectors.

Greater specific energy densities in lithium-ion batteries can be achieved by using three-dimensional (3D) porous current collectors, which allow for greater areal mass loadings of the electroactive material. In this paper, we present the use of embroidered current collectors for the preparation of thick, pouch-type Li-ion batteries. Experiments were performed on LiFePO4 (LFP) water-based slurries using styrene-butadiene rubber (SBR) as binder and sodium carboxymethyl cellulose (CMC) as thickener, and formulations of different rheological characteristics were investigated. The electrochemical performance (cyclic voltammetry, rate capability) and morphological characteristics of the LFP half-pouch cells (X-ray micro computed tomography and scanning electron microscopy) were compared between the formulations. An optimum electrode formulation was identified, and a mechanism is proposed to explain differences between the formulations. With the optimum electrode formulation, 350 µm casted electrodes with high mechanical stability were achieved. Electrodes exhibited 4-6 times greater areal mass loadings (4-6 mAh cm-2) and 50% greater electroactive material weight than with foils. In tests of half- and full-pouch embroidered cells, a 50% capacity utilization at 1C-rate and 11% at 2C-rate were observed, with a full recovery at C/5-rate. The cycling stability was also maintained over 55 cycles.

New Three-Dimensional Porous Electrode Concept: Vertically-Aligned Carbon Nanotubes Directly Grown on Embroidered Copper Structures.

New three-dimensional (3D) porous electrode concepts are required to overcome limitations in Li-ion batteries in terms of morphology (e.g., shapes, dimensions), mechanical stability (e.g., flexibility, high electroactive mass loadings), and electrochemical performance (e.g., low volumetric energy densities and rate capabilities). Here a new electrode concept is introduced based on the direct growth of vertically-aligned carbon nanotubes (VA-CNTs) on embroidered Cu current collectors. The direct growth of VA-CNTs was achieved by plasma-enhanced chemical vapor deposition (PECVD), and there was no application of any post-treatment or cleaning procedure. The electrochemical behavior of the as-grown VA-CNTs was analyzed by charge/discharge cycles at different specific currents and with electrochemical impedance spectroscopy (EIS) measurements. The results were compared with values found in the literature. The as-grown VA-CNTs exhibit higher specific capacities than graphite and pristine VA-CNTs found in the literature. This together with the possibilities that the Cu embroidered structures offer in terms of specific surface area, total surface area, and designs provide a breakthrough in new 3D electrode concepts.

Embroidered Copper Microwire Current Collector for Improved Cycling Performance of Silicon Anodes in Lithium-Ion Batteries.

Si holds great promise as an alloying anode material for Li-ion batteries with improved energy density because of its high theoretical specific capacity and favorable operation voltage range. However, the large volume expansion of Si during electrochemical reaction with Li and the associated adverse effects strongly limit its prospect for application. Here, we report on the use of three-dimensional instead of flat current collectors for high-capacity Si anodes in an attempt to mitigate the loss of electrical contact of active electrode regions as a result of structural disintegration with cycling. The current collectors were produced by technical embroidery and consist of interconnected Cu wires of diameter <150 µm. In comparison to Si/Li cells using a conventional Cu foil current collector, the embroidered microwire network-based cells show much enhanced capacity and reversibility due to a higher degree of tolerance to cycling.

Aqueous stabilisation of carbon-encapsulated superparamagnetic α-iron nanoparticles for biomedical applications.

Carbon-based nanomaterials, such as carbon-encapsulated magnetic nanoparticles (CEMNP, core@shell), show a wide range of desirable properties for applications in the biomedical field (clinical MRI, hyperthermia), for energy production and storage (hydrogen storage), for the improvement of electronic components and for environmental applications (water-treatment). However, this kind of nanoparticle tends to aggregate in water suspensions. This often hampers the processability of the suspensions and presents an obstacle to their application in many fields. Here the stabilisation of core-shell Fe-C nanoparticles by surface adsorbed polyvinyl-alcohol (PVA) is presented. Different PVA/CEMNP mass ratios (9, 36, 144 and 576 w/w) were studied. Several characterisation techniques were used in order to determine the size distribution of the particles and to optimize the PVA/CEMNP ratio. A good colloidal stability was obtained for spherical nanoparticles about 50 nm in diameter containing several superparamagnetic Fe cores. The nanoparticles were found to be isolated and well dispersed in solution. The use of PVA for coating carbon-encapsulated Fe nanoparticles does not only result in a good colloidal stability in aqueous suspensions, but the resulting particles also show low cytotoxicity and an interesting cell internalization behaviour. The simple stabilization method developed here can likely be extended to other core@shell nanoparticle systems as well as other carbon-based nanomaterials in the future.