1,720,989 research outputs found
Two new siloxanic proton-conducting membranes - Part I. Synthesis and structural characterization
No full textThe development of stable polymer electrolytes having good proton conductivity, low cost and operating at medium temperatures represent a crucial step in the evolution of polymer electrolyte fuel cells. We describe two new siloxanic proton-conducting membranes that were synthesized through a two-stage protocol. In the first stage, a poly(methyl hydrosiloxane) precursor (P) bearing siloxane side chains with sulfonic acid groups was prepared. In the second step, the hydrolysis of pristine precursor or its derivative obtained by grafting siloxane chains on P yielded two types of membranes with the formulas {Si(CH3)3O[Si(CH3)HO]21.26–[Si(CH3)((CH2)3SO3H)O]1.8–[Si(CH3)((CH2)3Si(CH3)2O–)–O]14–Si(CH3)3}n (A) and {Si(CH3)3O[Si(CH3)HO]21.26–[Si(CH3)((CH2)3SO3H)O]1.8–[Si(CH3)((CH2)3–(Si(CH3)2O–)w)–O]v[Si(CH3)((CH2)3Si(CH3)2O–)-O]14− vSi(CH3)3}n (B), with w = 20.31. Polymer membranes of A and B were prepared
by means of a hot-pressing process at 80 °C and 10 t/cm2. Scanning electron microscopy showed that A and B are rubbery materials with rough and transparent surfaces. Thermogravimetric investigations performed under air atmosphere disclosed that A and B are thermally stable
up to at least 198 °C. DSC measurements yielded Tg(s) of −44 and −60 ◦C for A and B, respectively. The polymers exhibit ionic exchange capacities of 0.33 (A) and 0.15 meq/g (B). FT-IR and FT-Raman investigations revealed that the polymers consist of reticulated siloxane networks with pendant silicone chains having sulfonic acid groups
Hybrid inorganic-organic polymer electrolytes: synthesis, FT-Raman studies and conductivity of {Zr[(CH2CH2O)8.7]r/(LiClO4)z}n network complexes
No full textThis paper describes the synthesis and characterization of three-dimensional hybrid inorganic-organic networks prepared by a polycondensation reaction between Zr(O(CH2)3CH3)4 and polyethylene glycol 400 (PEG400). Eleven hybrid networks doped with varying concentrations of LiClO4 salt were prepared. On the basis of analytical data and FT-Raman studies it was concluded that these polymer electrolytes consist of inorganic-organic networks with zirconium atoms bonded together by PEG400 bridges. These polymers are transparent with a solid rubber consistency and are very stable under inert atmosphere. Scanning electron microscopy revealed a smooth glassy surface. X-ray fluorescence microanalysis with energy dispersive spectroscopy demonstrated that all the constituent elements are homogeneously distributed in the materials. Thermogravimetric measurements revealed that these materials are thermally stable up to 262°C. Differential Scanning Calorimetry measurements indicated that the glass transition temperature Tg of these inorganic-organic hybrids varies from -43 to -15°C with increasing LiClO4 concentration. FT-Raman investigations revealed the TGT (T = trans, G = gauche) conformation of polyether chains and allowed characterization of the types of ion-ion and ion-polymer host interactions in the bulk materials. The conductivity of the materials at different temperatures Was determined by impedance spectroscopy over the 20 Hz-1 MHz frequency range. Results indicated that the materials conduct ionically and that their ionic conductivity is strongly influenced by the segmental motion of the polymer network and the type of ionic species distributed in the bulk material. Finally, it is to be highlighted that the hybrid network with a n(Li)/n(O) molar ratio of 0.0223 shows a conductivity of ca. 1 X 10-5 S/cm at 40°
Synthesis and structure of electrolytic complexes based on alpha-hydro-omega-oligo(oxyethylene)hydroxy-poly [oligo(oxyethylene)oxydimethylsililene] and delta-MgCl2
No full textAn alternated copolymer with the formula alpha-hydro-omega-oligo(oxyethylene)hydroxy-poly[oligo(oxyethylene)oxydimethylsililene] and a molecular weight of 9860 was synthesized. Doping of this polymer with the anhydrous salt delta-MgCl2 resulted in a new magnesium electrolytic complex poly[PEG400-alt-DEOS]/(MgCl2)0.26. The structural hypothesis for the polymer was proposed on the basis of elemental analyses and molecular weight. Detailed H-1-, C-13, and Si-29-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
Hybrid inorganic-organic polymer electrolytes: synthesis, structure and conductivity mechanism
No full textPolymer 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 electrodes (3D-HION-APE), zeolitic inorganic–organic polymer electrodes (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
A lithium Z-IOPE ionomer based on PEG600, (CH3)2SnCl2, and Li3Fe(CN)6
No full textIn this report, the preparation of a new zeolitic inorganic-organic polymer electrolyte (Z-IOPE) ionomer material by using (CH3)2SnCl2, Li3Fe(CN)6, and poly(ethylene glycol)600 as precursors is described. Scanning electron microscopy measurements,vibrational spectroscopy studies (far infrared, medium infrared, Raman laser), UV-visible investigations and microanalytical data gave detailed insight about the morphological and structural characteristics of this electrolytic complex and about the ion-ion/ion-polymer interactions in the system. Thermogravimetric and differential scanning calorimetry studies indicated that: (i) the material is stable up to about 140 °C; (ii) the Tg is equal to −50.5 °C; (iii) a crystallization process occurs at 20.9°C. 1H and 7Li nuclear
magnetic resonance measurements of the linewidth, spin-lattice relaxation, and pulsed field gradient diffusion were carried out suggesting the correlation of the lithium dynamics with polymer mobility. The conductivity mechanism in bulk material was investigated by electrical spectroscopy in the 10 mHz to 1 GHz range, between −60 and 80°C. The results were interpreted in terms of the relaxation events detected in the real and imaginary components of dielectric and conductivity spectra. The overall investigation led to the conclusion that the material conducts ionically, with a conductivity of 3.9x10−5 S/cm at 25.1°C with unity lithium transport number
Effect of subcritical CO2 on the structural and electrical properties of ORMOCERS-APE systems based on Zr and Al
No full textTwo series of hybrid inorganic–organic polymer electrolytes of the organically modified ceramics as polymer electrolytes (ORMOCERS-APE) type with formulas {Al[O(CH2CH2O)8.7]ρ/(LiClO4)z}n (1.85 ≤ ρ ≤ 2.24, 0 ≤ z ≤1.06) and {Zr[O(CH2CH2O)8.7]ρ/(LiClO4)z}n
(1.80 ≤ ρ ≤ 1.99, 0 ≤ z ≤ 0.90) were treated with CO2 in subcritical conditions (293 K and 5 MPa). The effect of CO2 on the samples was investigated by using ESEM, thermal analysis (TG and DSC) and broad band dielectric spectroscopy (BDS).
Both complexes {Al[O(CH2CH2O)8.7]ρ/(LiClO4)z}n and {Zr[O(CH2CH2O)8.7]ρ/(LiClO4)z}n after CO2 treatment exhibited a change in the segmental relaxation with respect to the untreated samples. This phenomenon has been interpreted in terms of higher portion of free volume in the samples. The CO2 treatment primarily lowered the conductivity of {Al[O(CH2CH2O)8.7]ρ/(LiClO4)z}n complexes of about one order of magnitude, as opposed to {Zr[O(CH2CH2O)8.7]ρ/(LiClO4)z}n complexes, where an increment of two orders of magnitude was observed. In both cases the conductivity of the treated and untreated materials versus the reciprocal absolute temperature presents the typical Vogel–Tamman–Fulcher (VTF) behavior. The different effects on the conductivities of the treated complexes are explained in terms of the modified anion-trapping ability of Al centers and in terms of the interactions of subcritical CO2 with the host polymer and the salt. Insight about the conductivity mechanisms were provided by the study of the VTF parameters and the relaxation times determined from the Debye peaks of the imaginary resistivity, the imaginary permittivity and the correlated motion analysis
Zeolitic inorganic-organic polymer electrolytes: synthesis,characterization and ionic conductivity of a material basedon oligo(ethylene glycol) 600, (CH3)2SnCl2 and K4Fe(CN)6
No full textThis 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 at 21.3 °
Effect of subcritical CO2 on ionic conductivity of [Al[O(CH2CH2O)8.7]r/(LiClO4)z]n hybrid inorganic-organic networks
No full textThe aim of this work is to study the effect of CO2 under pressure on hybrid inorganic–organic polymer electrolytes, by using broad band dielectric spectroscopy (BDS) in the frequency interval 40 Hz–10 MHz and in the temperature range of −80 to 120 °C.
Eleven inorganic–organic hybrid materials of the ORMOCERs type, with general formula {Al[O(CH2CH2O)8.7]ρ/(LiClO4)z}n were treated by applying CO2 at 293 K and 5 MPa. The results demonstrated that the CO2 treatment generally depressed the conductivity of about one order of magnitude. The decreased conductivity in treated complexes is explained in terms of a smaller anion-trapping ability of the Al centers.
Residual CO2 molecules are likely to inhibit the interaction of the perchlorate anions with Al centers within the structure. Segmental motion of the polymer chains plays a crucial role in the conductivity of investigated samples, while the ion-hopping phenomenon is the most important charge transfer mechanism both in the pristine and CO2 treated materials.
Equivalent conductivity studies have elucidated the different ionic species present at various salt concentrations and gave insight about the role of CO2 in modifying the transport properties of the samples
Conductivity, thermal stability and morphology of a new Z-IOPE inorganic-organic network with the formula [FexSny(CH3)2y(CN)zClv(CH2nH4n+2On+1)Kl]
No full textThis paper reports accurate studies on the morphology, thermal stability and electrical spectroscopy of a zeolitic inorganic-organic polymer electrolyte (Z-IOPE) with the formula [FexSny(CH3)2y(CN)zCly(C2nH4n+2On+1)Kl]. This material was prepared by means of a sol-gel process. A possible mechanism of the sol-gel process is proposed. Scanning electron microscopy showed that the Z-IOPE resembles a gummy paste with a rough texture and grains on the surface of the bulk material. Thermogravimetric investigations indicated that the material is thermally stable up to approximately 200°C. A detailed study of the mechanism of ion conduction in this system was carried out using impedance spectroscopy in the 20 Hz to 1 MHz range. The analysis of real and imaginary components of conductivity spectra indicated that a full characterization of the AC electrical response for this Z-IOPE system requires an equivalent circuit analysis for frequencies lower than 10 kHz and correlated ionic motion analysis based on the Universal Power Law for frequencies higher than 10 kHz. These studies demonstrated that the Z-IOPE material conducts ionically by a mechanism mainly regulated by segmental motion of the host material, and that charge migration by ion hopping between equivalent coordination sites is not to be completely excluded in the host network. Finally, the conductivity of 4.77 x 10-5 S/cm at 25°
Interplay Between Structure and Conductivity in Imidazolium-based Ionic Liquids as Electrolytes for Magnesium Batteries
No full textThe search for new electrolytes is one of the most challenging aspects in the development of secondary batteries based on Li and Mg ions.
The state of the art for Mg electrolytes is mainly constituted by organo-Mg compounds; in general, they show good Mg deposition and dissolution performance, high Coulombic efficiency and in some cases a wide electrochemical stability window. The main drawback of this class of materials is associated with their dissolution in ethereal-based solvents characterized by a high vapor pressure and flammability.
Nevertheless, the use of high-boiling solvents is known to lead to: (a) a decrease in the electrolyte conductivity; and (b) a decrease in the electrode reaction rate, which limits their practical applicability [2]. Ionic liquids (ILs) are salts that are molten at room temperature. ILs are also characterized by: (a) negligible vapor pressure; (b) high thermal stability; and (c) low flammability.
Only a few examples of the applicability of ILs as electrolytes for secondary Mg batteries are reported in the literature. Several issues regarding the conductivity mechanisms, formation of the solid-electrolyte interface (SEI) and long-term performance of these systems are still open questions.
From a fundamental point of view, the interplay between the ILs nanostructure and the conductivity is a crucial point to clarify the effect of the IL matrix on the migration mechanism of Mg2+ ions. In this report, a comparison between two Mg electrolytes based on Ethyl-methylimidazolium tetrafluoroborate (EMImBF4) and Ethyl-methylimidazolium chloride/AlCl3 (EMImCl/(AlCl3)1.5) ILs is proposed. Both ionic liquids are doped with different amounts of δ-MgCl2 , to achieve a sufficient conductivity of Mg ions.
The correlation between structure, thermal properties and conduction mechanism of the resulting EMImBF4/(δ-MgCl2) and [EMImCl/(AlCl3)1.5]/(δ-MgCl2)x is investigated by a variety of techniques: (a) FT-MIR and FIR at different temperatures; (b) differential scanning calorimetry (DSC); and (c) broadband electrical spectroscopy (BES).
BES measurements were undertaken to elucidate the electrical response of the electrolytes in terms of dielectric and polarization phenomena. At T Tm , three and four interdomain polarization events are detected respectively for EMImBF4 and [EMImCl/(AlCl3)1.5]. These polarization events are associated with the presence of cation and anion nanocluster aggregates with different permittivities
- …
