Maria Assunta Navarra

New, high temperature superacid zirconia-doped Nafion™ composite membranes

This study reports the synthesis and the characterization of composite, proton-conducting membranes prepared by dispersing in a Nafion matrix a highly functionalized inorganic filler, i.e. superacid zirconia. The results demonstrate that the surface properties of this unique ceramic filler play a key role in promoting high hydration level and enhanced acidity, which in turn reflect in improved thermal and transport properties of the composite membranes. We show that these membranes, with an optimum of 5% of superacid zirconia content, have a high conductivity which remains stable at temperature levels where the ionic transport of plain Nafion, as well as of conventional Nafion-based composite membranes, usually decays. These results suggest that this new type of Nafion composite membrane may be successfully used as an improved separator in polymer-electrolyte membrane fuel cells.

Silica-Added, Composite Poly(vinyl alcohol) Membranes for Fuel Cell Application

In this work we report the synthesis and the characterization of poly(vinyl alcohol) (PVA)-based proton-conducting membranes. In particular, we describe a cross-linking process of PVA with glutaraldehyde, which gives riseto membranes with enhanced morphological, thermal, and electrochemical characteristics. The critical role of the dispersion of a SiO 2 -based ceramic filler in promoting liquid retention and in enhancing the proton conductivity of composite PVA-based membranes is also discussed.

Ionic Liquid‐Based Membranes as Electrolytes for Advanced Lithium Polymer Batteries

Gel-type polymer electrolytes are formed by immobilizing a solution of lithium N,N-bis(trifluoromethanesulfonyl)imide (LiTFSI) in N-n-butyl-N-ethylpyrrolidinium N,N-bis(trifluoromethanesulfonyl)imide (Py₂₄TFSI) ionic liquid (IL) with added mixtures of organic solvents, such as ethylene, propylene and dimethyl carbonates (EC, PC, and DMC, respectively), into a poly(vinylidenefluoride-co-hexafluoropropylene) (PVdF-HFP) matrix, and their properties investigated. The addition of the organic solvent mixtures results in an improvement of the ionic conductivity and in the stabilization of the interface with the lithium electrode. Conductivity values in the range of 10⁻³-10⁻²  S cm⁻¹ are obtained in a wide temperature range. These unique properties allow the effective use of these membranes as electrolytes for the development of advanced polymer batteries based on a lithium metal anode and an olivine-type lithium iron phosphate cathode.

Composite Poly(ethylene oxide) Electrolytes Plasticized by N‐Alkyl‐N‐butylpyrrolidinium Bis(trifluoromethanesulfonyl)imide for Lithium Batteries

We report a new class of quaternary polymer electrolyte membranes that comprise poly(ethylene oxide) (PEO), lithium trifluoromethanesulfonylimide (LiTFSI), N-alkyl-N-butylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PyrA,4 TFSI) as an ionic liquid, and a SiO₂ filler. The results of differential scanning calorimetry indicate that the addition of SiO₂ and different ionic liquids induces a decrease in the PEO melting enthalpy, which thereby increases the ionic conductivity and the Li transference number. The electrochemical stability is proved by using impedance spectroscopy and cyclic voltammetry. Galvanostatic cycling of Li/LiFePO₄ cells, which comprise the quaternary polymer electrolytes, revealed their superior performance compared to conventional PEO-Li salt electrolytes. In the course of this investigation, a synergistic effect of the combined ionic liquid-ceramic filler modification could be proved at temperatures close to 50 °C.

A Structural Study on Ionic-Liquid-Based Polymer Electrolyte Membranes

We have investigated novel proton conducting membranes synthesized through the gelification of poly(vinylidene fluoride-co-hexafluoropropylene) in aprotic ionic liquids. Mobile protons were introduced by doping the system with the strong bis(trifluoromethanesulfonyl)imide acid (HTFSI), which is chemically compatible with the ionic liquids through the common TFSI- anion. The obtained membranes are thermally stable up to 115°C set by the melting of the polymer phase. At this temperature, the conductivity is on the order of 10-2 S cm-1. Raman and infrared spectroscopy show no chemical interactions between the components, indicating that the bulklike nature of the doped ionic liquids preserved within the membrane, as is the thermal stability and the high conductivity.

Novel, Ionic-Liquid-Based, Gel-Type Proton Membranes

We report a preliminary study on novel protonic membranes, obtained by the gelification of a selected polymer matrix in a highly stable ionic liquid solvent, i.e., 1,2-dimethyl-3--propylimidazolium bis(trifluoromethylsulfonyl)imide (DMPI-Im). The addition of an acid, chemically compatible with the ionic liquid thanks to the equality between the anionic components, gives rise to a reasonably high conductivity which, together with the good mechanical and thermal stability as well as an excellent control on the methanol crossover rate, make the membranes of interest for practical applications.

Preparation and Characterization of Nanocomposite Polymer Membranes Containing Functionalized SnO2 Additives

In the research of new nanocomposite proton-conducting membranes, SnO2 ceramic powders with surface functionalization have been synthesized and adopted as additives in Nafion-based polymer systems. Different synthetic routes have been explored to obtain suitable, nanometer-sized sulphated tin oxide particles. Structural and morphological characteristics, as well as surface and bulk properties of the obtained oxide powders, have been determined by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier Transform Infrared (FTIR) and Raman spectroscopies, N2 adsorption, and thermal gravimetric analysis (TGA). In addition, dynamic mechanical analysis (DMA), atomic force microscopy (AFM), thermal investigations, water uptake (WU) measurements, and ionic exchange capacity (IEC) tests have been used as characterization tools for the nanocomposite membranes. The nature of the tin oxide precursor, as well as the synthesis procedure, were found to play an important role in determining the morphology and the particle size distribution of the ceramic powder, this affecting the effective functionalization of the oxides. The incorporation of such particles, having sulphate groups on their surface, altered some peculiar properties of the resulting composite membrane, such as water content, thermo-mechanical, and morphological characteristics.

PVdF-based membranes for DMFC applications

This paper reports the synthesis and the properties of microporous, ceramic-added, composite poly(vinylidene) fluoride (PVdF)-based proton conducting membranes for direct methanol fuel cells (DMFCs). The favorable characteristics of these membranes are an high and stable conductivity, a proton transport mechanism not critically related to the water content, the low cost, and the low methanol crossover. Tests in a methanol-air laboratory cell demonstrate the applicability of these membranes in DMFCs.

Stabilization of different conformers of bis(trifluoromethanesulfonyl)imide anion in ammonium-based ionic liquids at low temperatures.

The infrared absorption spectra of two ionic liquids with bis(trifluoromethanesulfonyl)imide (TFSI) as an anion and ammonium with different alkyl chains as cations are reported as a function of temperature. Using the comparison with ab initio calculations of the infrared-active intramolecular vibrations, the experimental lines were ascribed to the various ions composing the ionic liquids. In the liquid state of the samples, both conformers of the TFSI ion are present. In the solid state, however, the two conformers survive in N-trimethyl-N-propylammonium bis(trifluoromethanesulfonyl)imide (TMPA-TFSI), while only cis-TFSI is retained in N-trimethyl-N-hexylammonium bis(trifluoromethanesulfonyl)imide (TMHA-TFSI). We suggest that the longer alkyl chains of the former compound stabilize the less stable conformer of TFSI by means of stronger interactions between anions and cations.

Synthesis and Characterization of Cellulose-Based Hydrogels to Be Used as Gel Electrolytes

Cellulose-based hydrogels, obtained by tuned, low-cost synthetic routes, are proposed as convenient gel electrolyte membranes. Hydrogels have been prepared from different types of cellulose by optimized solubilization and crosslinking steps. The obtained gel membranes have been characterized by infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis, and mechanical tests in order to investigate the crosslinking occurrence and modifications of cellulose resulting from the synthetic process, morphology of the hydrogels, their thermal stability, and viscoelastic-extensional properties, respectively. Hydrogels liquid uptake capability and ionic conductivity, derived from absorption of aqueous electrolytic solutions, have been evaluated, to assess the successful applicability of the proposed membranes as gel electrolytes for electrochemical devices. To this purpose, the redox behavior of electroactive species entrapped into the hydrogels has been investigated by cyclic voltammetry tests, revealing very high reversibility and ion diffusivity.