M.L. Di Vona

Transport and equilibrium characteristics of γ-lithium vanadium bronze

Abstract The diffusion coefficient of Li + in the γ-lithium vanadium bronze (Li 1+ x V 3 O 8 ) has been measured with the long-pulse galvanostatic technique. Values ranging from 1.7×10 −7 cm 2 s −1 , at x =0.3, to 2.2×10 −8 cm 2 s −1 , at x = 1.4, have been measured. The thermodynamic factors, d ln a/d ln c , determined from the OCV/ x curve and from voltage relaxation after the current pulse, have a mean value of ∼15. The pseudo two-phase region observed in the OCV/ x curve at high Li + concentrations seems attributable to ordering of Li + in specific sites and to alteration of the unit cell. This process is reversible as shown by X-ray diffractometry. Finally, from OCV/ t plots at different x , the partial molar entropy of Li + was determined. The values, on account of the large d E ( x )/d t measured, are higher than those found for V 6 O 13 or TiS 2 .

Water Activity Coefficient and Proton Mobility in Hydrated Acidic Polymers

Water vapor sorption and proton conductivity data of composite and cross-linked sulfonated aromatic polymers, sulfonated (poly ether ether ketone) (SPEEK) and sulfonated (poly phenyl sulfone) (SPPSU), determined at various temperatures and relative humidities, are used to determine effective water activity coefficients and proton mobilities in these ionomers. The data are challenged with classical physico-chemical laws for electrolyte solutions. The concentration dependence of water activity coefficients in hydrated aromatic polymers is related to an internal pressure exerted by the polymer, which is of the order of the tensile strength of the membranes. The strong concentration dependence of proton mobility is attributed to the particular environment that protons experience inside the nanometric hydrated channels with immobilization of protons near sulfonate groups situated on the channel boundaries. At high proton concentration, the percolation threshold of hydrated channels is observed in SPEEK, which presents hydrated nanochannels with higher tortuosity than Nafion or SPPSU. In SPEEK-silylated poly-phenyl-sulfone (SiPPSU) composites, this percolation threshold is not observed, pointing to special interface paths for conduction.

Behaviour of polyaniline electrodes in aqueous and organic solutions

Abstract Polyaniline (PAn) has been obtained in acidic solutions, chemically (by oxidation with (NH 4 ) 2 S 2 O 8 ), and electrochemically (by potential The reduction/oxidation processes of PAn are basically the same in aqueous acidic solutions and in Li + -containing organic solutions. The fully oxid

Effects of anion substitution on hydration, ionic conductivity and mechanical properties of anion-exchange membranes

Anion-conducting ionomers were synthesized by the chloromethylation of polysulfone (PSU) followed by the formation of quaternary ammonium groups by a reaction with trimethylamine (TMA) or 1,4-diazabicyclo[2.2.2]octane (DABCO). The degree of functionalization was determined by 1H NMR and titration. Anions (F−, Cl−, Br−, SO42−, NO3−, CO32−, HCO3−, CH3CO2−, and OH−) were substituted by ion exchange in aqueous solution. Water uptake, ionic conductivity and mechanical properties of various ionomers were determined. Hydration has a large influence on both ionic conductivity and mechanical properties: ionic conductivity increases with water uptake, whereas the Young’s modulus decreases. Hydroxide and fluoride containing ionomers present a particularly large ionic conductivity.

Anion-conducting sulfaminated aromatic polymers by acid functionalization

A simple synthesis technique for the preparation of anionic conducting membranes is presented. In the first step, poly-ether-ether-ketone (PEEK) reacts with chlorosulfonic acid to produce chlorosulfonated PEEK, which in a second step is transformed by reaction with a secondary amine, dimethyl- or diethylamine, into sulfaminated PEEK. The sulfaminated PEEK is cast and the membranes are functionalized in a last step by reaction with various aqueous acid solutions, including HCl, HBr, HNO3, H2SO4, and H3PO4. The spectroscopic, thermal, mechanical, permeability and electrical properties of the membranes are determined and discussed. The combination of appealing properties, such as high elastic modulus (∼1300 MPa), high thermal stability, low cation permeability, respectable anionic conductivity (2–4 mS cm−1), and a relatively simple and inexpensive synthesis make these new ionomers very promising for applications especially in acidic media, like in vanadium redox flow batteries.

A3.2 - Enzyme free sensor based on affinity viscosimetry for detection of glucose

The growing demand of miniaturization of cell cultivation new approaches towards measuring and sensing bio-analytes need to be addressed to overcome the challenge of small volumes (less than 150μl) containing small amounts of analytes. Most of the available glucose sensors monitor the glucose concentration with the help of enzymes, which become very unstable in terms of long time measurement and consume glucose during the measurement becoming not available anymore for the cells. Therefore, the focus was set on applying an enzyme-free glucose sensor based on a microelectromechanical system (MEMS).

Affinity Viscosimetry Sensor for Enzyme Free Detection of Glucose in a Micro-Bioreaction Chamber

With the growing demand of miniaturization of cell cultivation a new approach towards measuring and sensing bio-analytes needs to be made due to the problem of small volumes (less than 150μl) containing small amounts of analytes. Most of the available glucose sensors monitor the glucose concentration with the help of enzymes, which become very inaccurate in terms of long time measurement and uses (i.e. consumes) glucose during the measurement becoming not available anymore for the cells. Therefore, we focused on applying an enzyme-free glucose sensor based on a microelectromechanical system (MEMS).

Polymer electrolyte membrane development for Direct Methanol Fuel Cells powering portable microelectronic devices

Functions of portable electronic equipments, such as portable telephones, lap-top computers and digital cameras, have diversified and the power consumption of such portable electronic equipments has increased considerably due to their diversified functions. The batteries presently used in portable electronic equipments are lithium-ion secondary batteries. They do not always satisfy the userpsilas needs, because the time per charge is relatively short and the charging time is relatively long. Since it is expected that the energy density required by portable electronic equipments will become several times that presently required, there are demands to realize a power supply that may replace lithium-ion secondary battery.

Proton-Conducting Nanocomposites and Hybrid Polymers

This chapter is about proton-conducting nanocomposites and hybrid polymers. Before beginning to treat the different examples from literature, we must first define what we understand by the terms ‘nanocomposite’ and ‘hybrid polymer’. Their definitions are neither simple nor unanimous. A useful criteria for hybrid materials classification is based on their chemical nature: Class I where organic and inorganic components are dispersed and held together only by weak forces, such as Van der Waals interactions, and Class II where the organic and inorganic moieties are linked through strong bonds, such as covalent bonds [1]. In this context, Van der Waals interactions are considered to include permanent dipole interactions (Keesom forces, including also hydrogen bonds), interactions between permanent and induced dipoles (Debye forces) and interactions between induced dipoles (London forces). Class I hybrid materials and composites differ from each other in respect to the dimension of dispersion. However this difference is minimal when we consider ‘nanocomposites’. A nanocomposite is a material with nanometric domains of two coexisting phases without mutual solubility. In the following we will use the two terms, Class I and nanocomposite, as interchangeable. To clarify our definition, let us take the example of the most widely employed proton-conducting polymer today: Nafion. Nafion at high degree of humidification is itself a fascinating material, presenting hydrophilic and hydrophobic nanodomains and could, in a sense, already be considered as a nanocomposite. Figure 1 shows this microstructure schematically: one observes nanometric channels in the structure containing water molecules and dissociated sulfonic acid groups. Polymer domains are situated between these hydrophilic regions, where the hydrophobic perfluorated alkane chains are placed. No strong bonds exist between the two regions giving a relatively labile structure. The water containing domains are

Design of organic-inorganic hybrid membrane for polymer type fuel cell applications

Novel Organic-Inorganic hybrid materials based on highly sulfonated PolyEtherEtherKetone (PEEK) and PolyPhenylSulfone (PPSU) for application in fuel cells operating at intermediate temperatures were synthesized via simple, reproducible and inexpensive procedures. Thermal characterization showed that silicon groups chemically bonded to the polymer increase the oxidation stability of the membranes. The mechanical properties are superior to those of hard S-PEEK. Polymer blends with sulfonated and silylated PPSU showed particular behavior at 5% addition in terms of electrical conductivity and mechanical properties.