Binary Ferrihydrite Catalysts

A method of preparing a catalyst precursor comprises dissolving an iron salt and a salt of an oxoanion forming agent, in water so that a solution of the iron salt and oxoanion forming agent salt has a ratio of oxoanion/Fe of between 0.0001:1 to 0.5:1. Next is increasing the pH of the solution to 10 by adding a strong base followed by collecting of precipitate having a binary ferrihydrite structure. A binary ferrihydrite catalyst precursor is also prepared by dissolving an iron salt in water. The solution is brought to a pH of substantially 10 to obtain ferrihydrite precipitate. The precipitate is then filtered and washed with distilled water and subsequently admixed with a hydroxy carboxylic acid solution. The admixture is mixed/agitated and the binary ferrihydrite precipitate is then filtered and recovered

Van der Waals coefficients beyond the classical shell model

Van der Waals (vdW) coefficients can be accurately generated and understood by modelling the dynamic multipole polarizability of each interacting object. Accurate static polarizabilities are the key to accurate dynamic polarizabilities and vdW coefficients. In this work, we present and study in detail a hollow-sphere model for the dynamic multipole polarizability proposed recently by two of the present authors (JT and JPP) to simulate the vdW coefficients for inhomogeneous systems that allow for a cavity. The inputs to this model are the accurate static multipole polarizabilities and the electron density. A simplification of the full hollow-sphere model, the single-frequency approximation (SFA), circumvents the need for a detailed electron density and for a double numerical integration over space. We find that the hollow-sphere model in SFA is not only accurate for nanoclusters and cage molecules (e.g., fullerenes) but also yields vdW coefficients among atoms, fullerenes, and small clusters in good agreement with expensive time-dependent density functional calculations. However, the classical shell model (CSM), which inputs the static dipole polarizabilities and estimates the static higher-order multipole polarizabilities therefrom, is accurate for the higher-order vdW coefficients only when the interacting objects are large. For the lowest-order vdW coefficient C6, SFA and CSM are exactly the same. The higher-order (C8 and C10) terms of the vdW expansion can be almost as important as the C6 term in molecular crystals. Application to a variety of clusters shows that there is strong non-additivity of the long-range vdW interactions between nanoclusters

Free-standing sulfur-polypyrrole cathode in conjunction with polypyrrole-coated separator for flexible Li-S batteries

A free-standing sulfur-polypyrrole cathode and a polypyrrole coated separator were designed for flexible Li-S batteries. The free-standing sulfur-polypyrrole cathode was prepared by directly pasting a sulfur-coated polypyrrole (S@PPy) nanofiber composite on a flexible and conductive polypyrrole (PPy) film. Compared with carbonaceous matrixes, PPy has a strong interaction with polysulfides to mitigate the dissolution of polysulfides due to its unique chain structure and the lone pair electrons in the nitrogen atoms in PPy. In addition, the as-prepared PPy film not only shows excellent mechanical elasticity, but also possesses a rough surface, which can accommodate volume expansion, enhance the adhesion of active materials, and further trap the dissolved polysulfides. Due to the synergistic effect provided by the PPy film, the free-standing sulfur-polypyrrole cathode shows better electrochemical performance than the traditional cathode with S@PPy composite coated on Al foil. In order to further improve the cycling stability of Li-S batteries, a PPy coated separator was prepared, which acts as a fishing net to capture polysulfides and alleviate the shuttle effect, leading to a stable cycling performance. Moreover, the PPy layer coated on commercial separator is much lighter than many other free-standing interlayers reported previously. Considering the flexibility of the free-standing sulfur cathode and PPy coated separator, a soft-packaged flexible Li-S battery based on them has been designed and fabricated to power a device consisting of 24 light emitting diode (LED) lights. After repeated bending, the flexible Li-S battery can still maintain good performance, indicating the excellent mechanical flexibility of the designed Li-S battery