Study of the mechanism of the vanadium 4+/5+ redox reaction in acidic solutionsThe mechanism of the vanadium VO 2ϩ /VO 2 ϩ redox couple has been examined in acidic aqueous solutions. A detailed understanding of this chemistry is of interest for improving and optimizing the performance of vanadium redox-flow batteries, a promising electrochemical electricity storage technology. The vanadium 4ϩ/5ϩ redox reactions were studied at a rotating disk graphite electrode and polarization curves were obtained in sulfuric acid and perchloric acid, with varying pH and vanadium concentrations. The results were compared to model predictions for different mechanisms. The data were consistent with a model with a multistep chemical-electrochemical-chemical mechanism at low overpotentials, which changes to a multistep electrochemicalchemical-chemical mechanism at higher anodic or cathodic overpotentials. Unusually high Tafel slopes ͑350-450 mV/decade͒ were observed for the reduction of VO 2 ϩ at higher overpotentials. While this could not be directly explained by the model, insights gained through the use of the model can provide the basis for some suggestions.
using a solenoid coil with an iron core of 2.5 cm diameter. The core was positioned a couple of millimeters away from the substrate in order to provide a substantially uniform magnetic field over the extent of the substrate. This uniform magnetic field was sufficient to bias the magnetic moments of the beads in the direction perpendicular to the substrate. However, the same field had little effect on the magnetization of the micromagnets because of their very high shape anisotropy (extremely large magnetic energy would be required to turn the micromagnets' magnetization out of the plane). We report the facile microstructuring of conjugated polymers 1±5 (see Scheme 1) into hexagonally ordered twodimensional (2D) arrays by evaporative cooling with the subsequent condensation of water droplets onto a dilute solution of polymer in carbon disulfide. This report is the first example in which rigid rod-like polymers are microstructured into inverse hexagonal arrays by the formation, and subsequent crystallization of ªbreath figuresº. [1,2] Micro-and nanostructuring of organic semiconductors is of critical importance in the fabrication of photonic bandgap materials and heterojunction devices, such as photovoltaic cells and thin-film transistors.[3±5] A variety of templating methods based on self-assembly have been developed to create structures with micrometer and submicrometer dimensions. These include templating using ordered arrays of colloidal particles, [6±10] templating using an emulsion, [11] honeycomb structures formed by polymers with rod±coil architecture, [4,12±14]
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