María Angélica Santa Ana

Poly(acrylonitrile)–molybdenum disulfide polymer electrolyte nanocomposite

The synthesis, characterization and electrochemistry of a novel nanocomposite based on the co-intercalation of lithium and poly(acrylonitrile) (PAN) in molybdenum disulfide [Li0.6MoS2(PAN)1.2·0.5H2O] is described. The product, obtained chemically by treating LiMoS2 directly with a colloidal suspension of PAN in benzene, has a lamellar structure with an interlaminar distance of 1.15 nm. Elemental analysis, FT-IR spectra, thermal analysis and 7Li MAS-NMR spectra indicate that the polymer is co-intercalated with lithium in the MoS2 matrix. Lithium can be de-intercalated and intercalated electrochemically from the nanocomposite in the range x = 0.1–0.8. The structure of the interlamellar phase and the state of lithium in the LixMoS2(PAN)1.2 intercalates are discussed by comparing the behavior of both the potential and the diffusion coefficient with those of the poly(ethylene oxide) (PEO) and diethylamine (DEA) MoS2 intercalates. Both, the average quasi-equilibrium Li/Li+ potential of PAN nanocomposites (2.85 V) and the lithium diffusion coefficient (4.3 × 10−11 cm2 s−1) at room temperature are encouraging for exploring the use of this nanocomposite as an electrode.

Low‐Dimensional, Hinged Bar‐code Metal Oxide Layers and Free‐Standing, Ordered Organic Nanostructures from Turbostratic Vanadium Oxide

Both low-dimensional bar-coded metal oxide layers, which exhibit molecular hinging, and free-standing organic nanostructures can be obtained from unique nanofibers of vanadium oxide (VO(x)). The nanofibers are successfully synthesized by a simple chemical route using an ethanolic solution of vanadium pentoxide xerogel and dodecanethiol resulting in a double bilayered laminar turbostratic structure. The formation of vanadium oxide nanofibers is observed after hydrothermal treatment of the thiol-intercalated xerogel, resulting in typical lengths in the range 2-6 microm and widths of about 50-500 nm. We observe concomitant hinging of the flexible nanofiber lamina at periodic hinge points in the final product on both the nanoscale and molecular level. Bar-coded nanofibers comprise alternating segments of organic-inorganic (thiols-VO(x)) material and are amenable to segmented, localized metal nanoparticle docking. Under certain conditions free-standing bilayered organic nanostructures are realized.

Molybdenum Disulfide Intercalates with Special Transport Properties

Abstract Chemical modification of molybdenum disulfide based either in the restacking of the layered solid or the intercalation of lithium or organic donors as poly(ethylene oxide) or dialkylamines leads to products with improved transport properties. The products are mixed electronic-ionic conductors. Electrical conductivity, which in pressure compacted samples shows a clear anisotropic behavior, depends on the nature of the intercalated phase. For some dialkylamines [sgrave]-values of about 10−2 S cm−1 are reached. Electrode potentials available from charge/discharge curves in lithium electrochemical cells are mainly determined by both the trigonal prismatic-octahedral phase equilibrium in the matrix and the capacity of the guest for stabilizing Li+ ions in the interlaminar spaces. MoS2 phase change during lithium intercalation is also detected in the analysis of the 7Li-NMR linewidths of the LixMoS2 intercalates. Lithium diffusion coefficient analysis indicates that the mass transport of modified MoS2 is in general better than in the pristine compound.

Structure-Property Relationships in Molybdenum Disulfide Intercalates

The effects of host-guest and guest-guest interactions on the structure and electric inductivity of the products of the intercalation of electron pair donors as poly(ethylene oxyde), short chain (n=2-5) secondary amines, and long chain (n=12-18) amines into molybdenum disulfide are discussed. Although in most of the intercalates MoS 2 presents an octahedral conformation, induced principally by a host-guest charge transfer, in those with long chain amines predominate the hydrophobic intermolecular interactions bearing to products with different structural and transport properties.

QUANTUM CHEMICAL MODEL FOR LITHIUM ELECTROCHEMICAL INTERCALATION INTO MOLYBDENUM DISULFIDE

Voltage- and incremental charge capacity-composition curves for the electrochemical formation of intercalates LixMoS2 were analyzed at the molecular level by developing a quantum chemical model focused on the variation of the electron chemical potential. Experimentally observed trends of the charge capacity in the range 0<x<0.6 are successfully described by the global hardness index as defined within the density functional theory. Contrasting with classical descriptions like the gas lattice model assuming complete lithium-MoS2 one electron transfer, proposed model leads, agreeing with previous experimental evidence, to a system in which electron density is partially retained in the lithium atom. The model permits moreover to identify a sequence of octahedral and tetrahedral sites as the more favorable migration pathway for the diffusion of lithium through the interlaminar space

Lithium dynamics in molybdenum disulfide intercalation compounds studied by nuclear magnetic resonance

Cluster architecture and lithium motion dynamics are investigated in nanocomposites formed by the intercalation of lithium and a dialkylamine (diethylamine, dibutylamine and dipentylamine) in molybdenum disulfide by means of 7Li Nuclear Magnetic Resonance (NMR) technique. The present contribution illustrates the potential of the NMR techniques in the study of both the short range atomic structure and the local dynamics of ions in these intercalation compounds. Structural information is gained through measurements of the various interactions (such as dipolar and quadrupolar) that affect the lineshapes of the NMR spectra, while ion dynamics information is gained through the study of the effects that ionic motion has on the nuclear relaxation times, which are modulated by these interactions. The formation of lithium clusters in these nanocomposites is suggested by the Li-Li dipolar interaction strength calculated from the 7Li NMR data. The lithium spin-lattice relaxation is mainly due to the interaction between the quadrupolar moment of the 7Li nuclei and the fluctuating electric field gradient at the site of the nucleus, produced by the surrounding charge distribution. The relaxation mechanism is consistent with a fast exchange motion of lithium ions between the coordination sites within the aggregates.

Electrochemical behaviour of NN′-thiobisamines. Cyclic voltammetry in dimethyl sulphoxide with low water content

The electrochemical behaviour of NN′-thiobispiperidine and NN′-thiobismorpholine in dimethyl sulphoxide at low water content has been studied by cyclic voltammetry. Electro-oxidation in this medium, producing SO2 at the electrode surface, parallels the process observed by adding a Bronsted acid in which acid catalysed hydrolysis generates an intermediate species which is followed by a disproportionation process.

Solvent effects on the reduction potentials of nitroanilines

The influence of a number of aprotic solvents on the electrochemical reduction of ortho- and para-nitroanilines and their N-methyl derivatives has been studied. The reduction potentials, depending fundamentally on the acceptor properties of the medium, decrease with increasing solvent acceptor number. A similar effect is produced by intramolecular hydrogen-bonding interactions in ortho-derivatives. Intermolecular hydrogen-bonding interactions, occurring with derivatives having ‘free’ N–H protons, are transmitted through the molecule, enhancing the sensitivity of the NO2 group to the acceptor solvent.