Vanadium Oxide-Poly(3,4-ethylenedioxythiophene) Nanocomposite as High-Performance Cathode for Aqueous Zn-Ion Batteries: The Structural and Electrochemical Characterization.

In this work the nanocomposite of vanadium oxide with conducting polymer poly(3,4-ethylenedioxythiophene) (VO@PEDOT) was obtained by microwave-assisted hydrothermal synthesis. The detailed study of its structural and electrochemical properties as cathode of aqueous zinc-ion battery was performed by scanning electron microscopy, energy dispersive X-ray analysis, X-ray diffraction analysis, X-ray photoelectron spectroscopy, thermogravimetric analysis, cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy. The initial VO@PEDOT composite has layered nanosheets structure with thickness of about 30-80 nm, which are assembled into wavy agglomerated thicker layers of up to 0.3-0.6 µm. The phase composition of the samples was determined by XRD analysis which confirmed lamellar structure of vanadium oxide V10O24∙12H2O with interlayer distance of about 13.6 Å. The VO@PEDOT composite demonstrates excellent electrochemical performance, reaching specific capacities of up to 390 mA∙h∙g-1 at 0.3 A∙g-1. Moreover, the electrodes retain specific capacity of 100 mA∙h∙g-1 at a high current density of 20 A∙g-1. The phase transformations of VO@PEDOT electrodes during the cycling were studied at different degrees of charge/discharge by using ex situ XRD measurements. The results of ex situ XRD allow us to conclude that the reversible zinc ion intercalation occurs in stable zinc pyrovanadate structures formed during discharge.

Interactions in Electrodeposited Poly-3,4-Ethylenedioxythiophene-Tungsten Oxide Composite Films Studied with Spectroelectrochemistry.

Cyclic voltammograms and optical absorption spectra of PEDOT/WO3 composite films were recorded in order to identify possible interactions and modes of improved performance of the composite as compared to the single materials. Changes in the shape of redox peaks related to the W(VI)/W(V) couple in the CVs of WO3 and the composite PEDOT/WO3 films indicate electrostatic interactions between the negatively charged tungsten oxide species and the positively charged conducting polymer. Smaller peak separation suggests a more reversible redox process due to the presence of the conducting polymer matrix, accelerating electron transfer between tungsten ions. Electronic absorption spectra of the materials were analyzed with respect to changes of the shapes of the spectra and characteristic band positions. There are no noticeable changes in the position of the electronic absorption bands of the main chromophores in the electronic spectra of the composite film. Obviously, the interactions accelerating the redox performance do not show up in the optical spectra. This suggests that the existing electrostatic interactions in the composite do not significantly change the opto-electronic properties of components of the composite but resulted in the redistribution of fractions of polaron and bipolaron forms in the polymer.

Inner Coordination Sphere Control of Metal-Metal Superexchange in Ruthenium Dimers.

The dinuclear Ru(III) complexes trans-[{(NH(3))(4)Ru(py)}(2)(&mgr;-L)][PF(6)](4), where py represents pyridine and L represents 1,4-dicyanamidobenzene dianion (dicyd(2)(-)) derivatives dicyd(2)(-) (1), Me(2)dicyd(2)(-) (2), Cl(2)dicyd(2)(-) (3), and Cl(4)dicyd(2)(-) (4), have been prepared and characterized by electronic absorption spectroscopy and cyclic voltammetry. A crystal structure of the complex trans-[{(NH(3))(4)Ru(py)}(2)(&mgr;-dicyd)][PF(6)](4).(1)/(2)H(2)O showed the dicyd(2)(-) ligand to be approximately planar with the cyanamido groups in a syn configuration. Crystal structure data are space group P2(1), with a, b, and c = 7.826(3), 20.455(7), and 14.428(5) Å, respectively, beta = 95.76 (3) degrees, V = 2296.7(14) Å(3), and Z = 2. The structure was refined by using 3292 reflections with I > 2.5sigma(I) to an R factor of 0.069. Solid state magnetic susceptibility measurements of the Ru(III)-Ru(III) dimers showed diamagnetic behavior at room temperature, and this is suggested to be due to strong antiferromagnetic superexchange via the HOMO of the dicyd(2)(-) ligand. The bridging ligand dependence of metal-metal coupling in the Ru(III)-Ru(II) complexes of 1, 2, 3, and 4 in acetonitrile solution was demonstrated by the trend in comproportionation constants, 1.5 x 10(6), 5.7 x 10(6), 1.4 x 10(4), and 1.1 x 10(3), respectively. In addition, comparison to the analogous pentaammineruthenium dimers showed that the magnitude of metal-metal superexchange could be controlled by the nature of the spectator ligand. Spectroelectrochemical methods were used to acquire the absorption spectra of the mixed-valence complexes, and the intervalence band properties were modeled with PKS theory. Metal-metal coupling in the Ru(III)-Ru(II) complexes of 1, 2, 3, and 4 was analyzed by using Hush and CNS theories.