Michele Vittadello

Mechanism of ionic conductivity in poly(ethylene glycol 400)/(MgCl2)x polymer electrolytes: studies based on electrical spectroscopy

Abstract In this paper, eight solvent-free polymer electrolytes PEG400/(MgCl 2 ) x (0.00329≤ x ≤0.7000) were prepared in order to investigate the mechanism of ionic motion and the interactions existing in these systems. The study was carried out by impedance spectroscopy in the 20-Hz to 1-MHz range at different temperatures. Real and imaginary components of conductivity spectra in terms of equivalent circuit analysis (EC) and correlated ionic motion analysis based on a generalized universal power law (UPL) were investigated. Results revealed that in the PEG400/(MgCl 2 ) x , the ionic species formed in the bulk materials are crucial for the overall conductivity. Indeed, in PEG400/(MgCl 2 ) x , conductivity is ionic and takes place through hopping of the cationic species Mg 2+ and [MgCl] + between the coordination sites present along the polyethereal chains.

Vibrational Studies and Properties of Hybrid Inorganic-Organic Proton Conducting Membranes Based on Nafion and Hafnium Oxide Nanoparticles

In this report, we will describe the effect of different concentrations of HfO2 nanopowders on the structure and properties of [Nafion/(HfO2)n] membranes with n = 0, 3, 5, 9, 11, 13, and 15 wt %, respectively. Films were prepared by a solvent casting procedure using HfO2 oxoclusters and Nafion. Seven new homogeneous membranes were obtained with thicknesses ranging from 200 to 350 microm. Each membrane is characterized by a rough HfO2-rich surface and a smooth Nafion-rich surface, with different physical-chemical properties. Membrane characterization was accomplished by means of thermogravimetric analysis (TGA), morphological measurements (environmental scanning electron microscopy) and vibrational spectroscopy (Fourier transform infrared attenuated total reflectance spectroscopy and Fourier transform Raman spectroscopy). These systems can be described in terms of five types of water domains, Nafion-HfO2 species with well-defined stoichiometry surrounded by Nafion and hydrated hafnia. The highest conductivity at 125 degrees C (3.2 x 10-2 S x cm(-1)) was measured on the [Nafion/(HfO2)5] film by electrical spectroscopy, with a stability range of conductivity between 5 and 115 degrees C.

Photoelectron generation by photosystem II core complexes tethered to gold surfaces

By using a nondestructive, ultrasensitive, fluorescence kinetic technique, we measure in situ the photochemical energy conversion efficiency and electron transfer kinetics on the acceptor side of histidine-tagged photosystem II core complexes tethered to gold surfaces. Atomic force microscopy images coupled with Rutherford backscattering spectroscopy measurements further allow us to assess the quality, number of layers, and surface density of the reaction center films. Based on these measurements, we calculate that the theoretical photoelectronic current density available for an ideal monolayer of core complexes is 43 microA cm(-2) at a photon flux density of 2000 micromol quanta m(-2) s(-1) between 365 and 750 nm. While this current density is approximately two orders of magnitude lower than the best organic photovoltaic cells (for an equivalent area), it provides an indication for future improvement strategies. The efficiency could be improved by increasing the optical cross section, by tuning the electron transfer physics between the core complexes and the metal surface, and by developing a multilayer structure, thereby making biomimetic photoelectron devices for hydrogen generation and chemical sensing more viable.

The first lithium zeolitic inorganic–organic polymer electrolyte based on PEG600, Li2PdCl4 and Li3Fe(CN)6: part I, synthesis and vibrational studies

The synthesis of Li 2 PdCl 4 and Li 3 Fe(CN) 6 precursors, and the preparation of the first lithium Z-IOPE material obtained by reacting these precursors with poly(ethylene glycol)600 (PEG600) is reported. This new material has been obtained through a sol ⇒ gel and gel ⇒ plastic transition. FIR and MIR spectroscopy studies, Raman laser and UV-vis investigations and detailed compositional data allowed us to propose a structural hypothesis and to detect the interactions between ions and the coordinating segments of the host network. It has been concluded that: (1) this compound is a mixed inorganic-organic network in which clusters formed by palladium and iron complexes are bonded together by PEG bridges; (2) the conformation of polyether chains in the bulk material is of the TGT (T = trans, G = gauche) type. The conductivity of the proposed [Fe x Pd y (CN) z Cl v (C 2n H 4n+2 O n+1 )Li l ] is 5.3 × 10 -5 S cm -1 at 35.1 °C.

Ormosil/Sulfonated Polyetheretherketone-Based Hybrid Composite Proton Conducting Membranes

A modified silane bearing a sulfonic acid function (sulfonated diphenylsilanediole, SDPSD) was prepared and characterized. The resulting ormosil was mixed with sulfonated polyetheretherketone (SPEEK) with high degree of sulfonation (0.9) leading to homogeneous composite membranes. The formation of the composite substantially modified the properties of SPEEK in terms of water uptake and solubility. The structural and electrochemical performance of the components and of the composite were investigated with thermogravimetric analysis, field emission scanning electron microscopy, H-1 and Si-29 nuclear magnetic resonance, both in solution and in the solid state, and electrochemical impedance spectroscopy. Both conductivity values, as high as 0.1 S cm(-1), and H-1 diffusion coefficients of the composite SPEEK/SDPSD demonstrated that it possesses good proton transport characteristics up to 120 S C, and it is then suitable for application as an electrolyte in polymer electrolyte fuel cells operating at intermediate temperature

Zeolitic inorganic–organic polymer electrolytes: synthesis, characterization and ionic conductivity of a material based on oligo(ethylene glycol) 600, (CH3)2SnCl2 and K4Fe(CN)6

This paper reports the synthesis of a new Z-IOPE material based on poly(ethylene glycol) 600, (CH3)2SnCl2 and K4Fe(CN)6. This material was synthesized via a sol-gel transition. FIR and MIR spectroscopy studies together with detailed compositional data allowed us to propose a final structure for this Z-IOPE material. It was concluded that this compound is a mixed inorganic-organic network in which clusters formed by tin and iron complexes are bonded together by PEG 600 bridges. The conformation of polyethereal chains in the bulk material is of the TGT (T=trans, G=gauche) type. Impedance spectroscopy measurements revealed that the material has a conductivity of 4.77.10−5 S cm−1 at 21.3°C.

A Key concept in Magnesium Secondary Battery Electrolytes.

A critical roadblock toward practical Mg-based energy storage technologies is the lack of reversible electrolytes that are safe and electrochemically stable. Here, we report on high-performance electrolytes based on 1-ethyl-3-methylimidazolium chloride (EMImCl) doped with AlCl3 and highly amorphous δ-MgCl2 . The phase diagram of the electrolytes reveals the presence of four thermal transitions that strongly depend on salt content. High-level density functional theory (DFT)-based electronic structure calculations substantiate the structural and vibrational assignment of the coordination complexes. A 3D chloride-concatenated dynamic network model accounts for the outstanding redox behaviour and the electric and magnetic properties, providing insight into the conduction mechanism of the electrolytes. Mg anode cells assembled using the electrolytes were cyclically discharged at a high rate (35 mA g(-1) ), exhibiting an initial capacity of 80 mA h g(-1) and a steady-state voltage of 2.3 V.

Vibrational studies of the ion–polymer interactions in α-hydro-ω-oligo(oxyethylene)hydroxy-poly[oligo(oxyethylene)oxydimethylsililene]/δ-MgCl2

Abstract Polymer–polymer and salt–polymer interactions of seven electrolytic complexes based on α-hydro-ω-oligo(oxyethylene)hydroxy-poly[oligo(oxyethylene)oxydimethylsililene] and δ-MgCl 2 were studied. This aim was pursued by means of an accurate medium and far FT-IR spectroscopic analysis. By using the decomposition and difference spectroscopy techniques, intensity and frequency of terminal OH and CO stretchings were evaluated in order to detect the presence of anion clusters build up by the coordination of Cl − with -OH groups. The number of chlorine anions per chain coordinated magnesium was established. This analysis allowed us to gain a complete structural picture for these materials, pointing out three possible coordinations of magnesium by polyethereal chains.

Synthesis and structure of electrolytic complexes based on α-hydro-ω-oligo(oxyethylene)hydroxy-poly[oligo(oxyethylene)oxydimethylsililene] and δ-MgCl2

Abstract An alternated copolymer with the formula α-hydro-ω-oligo(oxyethylene)hydroxy-poly[oligo(oxyethylene)oxydimethylsililene] and a molecular weight of 9860 was synthesized. Doping of this polymer with the anhydrous salt δ-MgCl 2 resulted in a new magnesium electrolytic complex poly[PEG400-alt-DEOS]/(MgCl 2 ) 0.26 . The structural hypothesis for the polymer was proposed on the basis of elemental analyses and molecular weight. Detailed 1 H-, 13 C-, and 29 Si-NMR spectral investigations fully confirmed the structure of poly[PEG400-alt-DEOS]. Mid-infrared region (MIR) FT-IR studies of the polymer showed that it presents (1) a sufficient number of terminal hydroxyl groups to confer a substantial degree of dissolution and salt-dissociation in the polymer complex; and (2) polyethereal fragments in a conformational geometry close to TGT (T= trans , G= gauche ). The conductivity against temperature plot for this very amorphous magnesium polymer electrolyte demonstrated that the material conducts ionically by means of two types of charge migration mechanisms.

6 – Hybrid inorganic–organic polymer electrolytes

Abstract: Polymer electrolytes (PEs) are macromolecular systems capable of transporting charged species such as ions or protons. The main application of PEs is in energy conversion and storage devices such as batteries and fuel cells. The chapter overviews the synthesis, structure, physical and electrical properties of three classes of hybrid inorganic–organic PEs: three-dimensional hybrid inorganic–organic networks as polymer electrolytes (3D-HION-APE), zeolitic inorganic–organic polymer electrolytes (Z-IOPEs) and hybrid gel electrolytes (HGEs). The basic structure of the materials consists of organic macromolecules bridging inorganic clusters or species. The chapter also includes an overview of the methods used in the characterization of the structure and of the electrical conductivity of PEs, with a particular reference to the jump relaxation model.