Dynamic Rheological Analysis of MLVs and Lamellar Phases in the System C12E4 / D2O

AbstractThe mechanical properties of the lamellar phase, La, of the system C12E4/D2O were studied along an isoplethal path (30 wt% C12E4) in the temperature range 10 - 60°C. A dynamic analysis was determined by small strain oscillatory rheometry. The multilamellar vesicles ("MLVs") ("onions") were transformed by shearing the lamellar phase. The micellar phase was investigated by steady and dynamic rheological experiments. The micellar aggregate size increases slightly upon heating and the transition from micelles to lamellae appears to be a first order transition. The mechanical spectra of the lamellar phase show a strong dependence of the moduli on the frequency. This is typical of defective lamellar phases. They are different from MLVs mechanical spectra. The MLVs viscous and storage moduli are almost independent from the frequency and they exhibit the characteristics of a strong gel. The temperature of formation of the MLVs phase influences the mechanical properties of the MLVs. Three different packing states of the MLVs phase were observed in the temperature range 25 - 55°C

Probing membrane and interface properties in concentrated electrolyte solutions

This study deals with the membrane and interface electrical properties investigation by electrochemical impedance spectroscopy (EIS). The EIS is a powerful technique for characterizing electrical behavior of systems in which coupled electrical processes occur at different rates.A systematics tudy on the effect of solution concentration,temperature and velocity, on the electrical resistance of anion-and cation- exchange membranes (AEMs and CEMs) and their interfaces (electrical double layer and diffusion boundary layer), was carried out. At the best of our knowledge, for t he first time electrolyte concentrations up to 4 M were used for the study of membranes and interface by EIS. Moreover, Pulsed Gradient Spin Echo Nuclear Magnetic Resonance (PGSE-NMR)technique was used to measure the water self-diffusion coefficients in swelled membrane as a function of the solution concentration and temperature.These measurements gave additional important insights about the effect of the electrolyte solution and fixed charges concentration in membrane,on membrane microstructure and its transport and electrical properties. & 2014TheAuthors.PublishedbyElsevierB.V.ThisisanopenaccessarticleundertheCCBY This study deals with the membrane and interface electrical properties investigation by electrochemical impedance spectroscopy (EIS)

Transport Properties and Mechanical Features of Sulfonated Polyether Ether Ketone/Organosilica Layered Materials Nanocomposite Membranes for Fuel Cell Applications

In this work, we study the preparation of new sulfonated polyether ether ketone (sPEEK) nanocomposite membranes, containing highly ionic silica layered nanoadditives, as a low cost and efficient proton exchange membranes for fuel cell applications. To achieve the best compromise among mechanical strength, dimensional stability and proton conductivity, sPEEK polymers with different sulfonation degree (DS) were examined. Silica nanoplatelets, decorated with a plethora of sulfonic acid groups, were synthesized through the one-step process, and composite membranes at 1, 3 and 5 wt% of filler loadings were prepared by a simple casting procedure. The presence of ionic layered additives improves the mechanical strength, the water retention capacity and the transport properties remarkably. The nanocomposite membrane with 5% wt of nanoadditive exhibited an improvement of tensile strength almost 160% (68.32 MPa,) with respect to pristine sPEEK and a ten-times higher rate of proton conductivity (12.8 mS cm−1) under very harsh operative conditions (i.e., 90 °C and 30% RH), compared to a filler-free membrane. These findings represent a significant advance as a polymer electrolyte or a fuel cell application

Transport Properties in Polymer Nanocomposite Membranes Cataldo Simari

Doctorate school of Science and Technique: Mesophases and Molecular Materials "Bernardino Telesio", Ciclo XXVIII, a.a. 2015--2016The aim of this thesis has been to prepare and characterize innovative composite membranes for polymer electrolyte fuel cells (PEMFCs) applications. Among the different energy conversion devices based on polymer electrolytes, PEMFCs, both hydrogen (DHFC) and direct methanol (DMFC), seems to be one of the most promising clean energy technologies. As electrochemical devices able to directly convert the chemical energy of a fuel into electrical energy, PEMFCs offer interesting advantages in vehicular or portable applications , as the quick start, the high energy conversion efficiency (~ 50%), the reduced environmental impact for the low CO2 emissions (zero in the case where the primary fuel is hydrogen) and the flexibility respect to the fuel, in fact, besides hydrogen (DHFC), they can be fed for example with methanol (DMFC). However, considerable efforts are still needed to be able to achieve satisfactory performance in terms of efficiency, durability and cost for mass deployment of such technology. It is necessary to deal with some problems that concern the electrolyte membrane, such as the degradation of the materials, the low proton conductivity at low relative humidity (RH) and poor mechanical properties at temperature higher than 130 °C. Therefore, the development of high-performance proton conducting polymer electrolyte membranes is critical for the optimal power density and efficiency a PEMFC can achieve because membrane ohmic loss is the major cause of overpotential in the operational current range of the fuel cell. In recent years, increasing interest has been devoted to the development of high temperature proton conducting polymer electrolyte fuel cell systems. In fact, most of the shortcomings associated with the lowtemperature PEMFC technology based on perfluorosulfonic acid (PFSA) membranes can be solved or avoided by developing alternative membranes with suitable ionic conductivity and stability up to 150 °C. The increasing the operational temperature would result in increased performance of the cell because of easier and more efficient water management, higher reaction rates to the electrodes, improved CO tolerance by the anode electro-catalysts, faster heat rejection rates and better systems integration. It has been mentioned the possibility to feed PEMFCs systems with other fuel respect to hydrogen. In particular, direct methanol fuel cells (DMFCs) combine the merits of polymer electrolyte fuel cells fueled by H2 with the advantages of a liquid fuel, such as easy handling and high energy density. However, despite these advantages, also regard this devices there are still technical barriers to overcome for their widespread commercialization such as methanol crossover from anode to cathode through the proton exchange membrane. From the above, it is thus highly important to enhance the proton conductivity of the electrolyte membrane under low RH in order to accomplish higher PEMFCs performance. On the other hand, is essential to develop polymer electrolytes with reduced methanol cross-over for DMFC. The work presented in this thesis is the result of a Ph.D. project carried out during a period of about three years from 2012 – 2015, in the Physical Chemistry Soft Matter Laboratory “Mario Terenzi” (PC_SM Mario Terenzi) at the Department of Chemistry and Chemical Technologies in the University of Calabria. The thesis was written as part of the requirements for obtaining the doctor of philosophy degree. The overall objective of this doctoral thesis was to design, synthesize and evaluate innovative composite electrolytes with specific properties suitable for PEM fuel cells that operate at high temperatures (above 100 ° C ) and low RH and/or with low methanol permeability. To this purpose, three main classes of materials have been explored as nanoadditives to create nanocomposite membranes: (i) organo-modified TiO2 nanoparticles, (ii) layered materials based on clays (anionic and cationic) and graphene oxide and (iii) hybrids clays-carbon nanotubes. While, as concern the ionomers, perfluorosulfonic acid (Nafion®) and polyaromatic polymers (sulfonated Polyether Ether Ketone and Polybenzimidazole) have been evaluated. In my doctoral porject an attempt was made to conjugate an intense basic research in order to understand the molecular mechanisms at the basis of ionic conduction in such complex systems, and the design, synthesis and more comprehensive characterization of new nanocomposites with opportune requisites. For this purpose an deep study of the transport properties of the water confined within the electrolyte membranes has been performed by NMR spectrocopy (diffusometry, relaxometry and 1H spectral analysis) together to a wide physico-chemical, mechanical and electrochemical characterization in order to achieve a systematic understanding at a fundamental level of the effects of dimensionality, architecture and organization of these nanofillers on the properties of the ionomers and to exploit this knowledge for the preparation of high performance electrolytes. Some of the electrolytes membranes investigated during my PhD thesis were prepared and studied in the framework of the PRIN Project: NAMED-PEM “Advanced nanocomposite membranes and innovative electrocatalysts for durable polymer electrolyte membrane fuel cells”. The last part of this thesis concerns a research work arisen from a collaboration with ITM-CNR of the University of Calabria, on the Ion Exchange Membranes for Reverse Electrodialysis (RED) process. Here, the NMR techniques were used to study the water dynamics in anion- and cation- exchange membranes (AEMs and CEMs) in order to achieved additional important insights about the effect of the electrolyte solution, on membrane microstructure and its transport and electrical properties. The results of this research have been published in scientific international Journals and reported in appendix to the end of the thesis. During these years I have spent two stages periods abroad: 1) in the “Department of Materials Science and Engineering of the University of Ioannina, Ioannina (Greece)”, where I worked under the supervision of Prof. D. Gournis, my research has been focused on the synthesis of novel carbon-based materials as additives for nanocomposite membranes; 2) in Department of Physics & Astronomy of the Hunter College, New York (USA), where I worked under the supervision of Prof. S. Greenbaumn, I performed the High Pressure NMR investigation of water and methanol transport properties in sPEEK-based nanocomposite electrolytes. Two scientific papers, based on the results obtained during these stages, have been recently submitted and also reported in appendixUniversity of Calabri

Sulfonated Polyether Ether Ketone and Organosilica Layered Nanofiller for Sustainable Proton Exchange Membranes Fuel Cells (PEMFCs)

The ease and low environmental impact of its preparation, the reduced fuel crossover, and the low cost, make sulfonated polyether ether ketone (sPEEK) a potential candidate to replace the Nafion ionomer in proton exchange membrane fuel cells (PEMFCs). In this study, sPEEK was used as a polymer matrix for the preparation of nanocomposite electrolyte membranes by dispersing an organo-silica layered material properly functionalized by anchoring high phosphonated (PO3H) ionic groups (nominated PSLM). sPEEK-PSLM membranes were prepared by the solution intercalation method and the proton transport properties were investigated by NMR (diffusometry-PFG and relaxometry-T1) and EIS spectroscopies, whereas the mechanical properties of the membranes were studied by dynamic mechanical analysis (DMA). The presence of the organosilica nanoplatelets remarkably improved the mechanical strength, the water retention capacity at high temperatures, and the proton transport, in particular under harsh operative conditions (above 100 °C and 20–30% RH), usually required in PEMFCs applications

Hybrid nanostructured fillers for polymer electrolytes in the PEM Fuel Cells

Dottorato di Ricerca in Scienze e Tecnologie delle Mesofasi e dei Materiali Molecolari, XXV Ciclo, a.a. 2011-2012The present thesis is focused on the development of novel nancomposite membranes, prepared by the incorporation of two-dimensional inorganic layered structures such as (i) smectite clays (synthetic and natural), (ii) graphene oxide (GO), and (iii) layered double hydroxides (LDHs) with different compositions into the polymer matrix of Nafion, for use as electrolytes in Proton Exchange Membrane fuel cells. The characteristics of the membranes were studied mainly, in terms of transport properties by NMR spectroscopy, in order to study the water dynamics inside the electrolyte membranes. For this purpose the Pulse-Field-Gradient Spin-Echo NMR (PFGSENMR) method was employed to obtain a direct measurement of water self-diffusion coefficients on the water-swelled membranes in a wide temperature range (25-140 °C). This technique together with the 1H-NMR spectral analysis and NMR spin-lattice relaxation times (T1) conducted under variable temperature. Furthermore, both pristine materials (fillers and Nafion) as well as the resulted nanocomposite membranes were characterized by a combination of X-ray diffraction, FTIR spectroscopy, thermal analysis (DTA/TGA), Raman spectroscopies and scanning electronic microscopy (SEM).Università della Calabri

Composite Gel Polymer Electrolytes Based on Organo-Modified Nanoclays: Investigation on Lithium-Ion Transport and Mechanical Properties

Composite gel polymer electrolytes (GPEs) based on organo-modified montmorillonite clays have been prepared and investigated. The organo-clay was prepared by intercalation of CTAB molecules in the interlamellar space of sodium smectite clay (SWy) through a cation-exchange reaction. This was used as nanoadditive in polyacrylonitrile/polyethylene-oxide blend polymer, lithium trifluoromethanesulphonate (LiTr) as salt and a mixture of ethylene carbonate/propylene carbonate as plasticizer. GPEs were widely characterized by DSC, SEM, and DMA, while the ion transport properties were investigated by AC impedance spectroscopy and multinuclear NMR spectroscopy. In particular, 7Li and 19F self-diffusion coefficients were measured by the pulse field gradient (PFG) method, and the spin-lattice relaxation times (T1) by the inversion recovery sequence. A complete description of the ions dynamics in so complex systems was achieved, as well as the ion transport number and ionicity index were estimated, proving that the smectite clay surfaces are able to “solvatate” both lithium and triflate ions and to create a preferential pathway for ion conduction

A Novel Li+-Nafion-Sulfonated Graphene Oxide Membrane as Single Lithium-Ion Conducting Polymer Electrolyte for Lithium Batteries

Single lithium-ion conducting polymer electrolytes are an innovative concept of solid-state polymer electrolytes (SPEs) for lithium-battery technology. In this work, a lithiated Nafion nanocomposite incorporating sulfonated graphene oxide (sGO-Li+), as well as a filler-free membrane, have been synthesized and characterized. Ionic conductivities and lithium transference number, evaluated by electrochemical techniques after membrane-swelling in organic aprotic solvents (ethylene carbonate-propylene carbonate mixture), display significant values, with sigma approximate to 5 x 10(-4) S cm(-1) at 25 degrees C and t(Li+) close to unity. The absence of solvent leaching on thermal cycles is also noteworthy. The description at molecular level of the lithium transport mechanism has been carefully tackled through a systematic study by Li-7 NMR spectroscopy (pulsed field gradient-PFG and relaxation times), while the mechanical properties of the film electrolytes have been evaluated by dynamic mechanical analysis (DMA) in a wide temperature range. The electrochemical performances of the graphene-based electrolyte in Li/Li symmetric cells and in secondary cells using LiFePO4 as positive electrode show good compatibility and functionality with the Li-metal anode by forming a stable interphase, as well as displaying promising performance in galvanostatic cells