Dipartimento di Chimica e Tecnologie Chimiche - Tesi di Dottorato
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Questa collezione raccoglie le Tesi di Dottorato afferenti al Dipartimento di Chimica e Tecnologie Chimiche dell'Università della Calabria.
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Item Transport Properties in Polymer Nanocomposite Membranes Cataldo Simari(2015-12-15) Simari, Cataldo; Versace, Carlo; Nicotera, IsabellaThe 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 appendixItem New hybrid solar cell (СNT – RUTHENIUM DYE)(2012-12-06) Siprova, Svetlana; Versace, Carlo; De Filpo, Giovanni; Bartolino, RobertoNegli ultimi anni le applicazioni dei nanotubi di carbonio nel settore microelettronico sono notevolmente aumentate date le proprieta’ uniche. In particolare la conducibilita’ dei nanotubi fa si che essi trovino interessanti utilizzi nel settore fotovoltaico. Questo lavoro si concentra sulla progettazione di una cella solare ibrida a base di nanotubi di carbonio e dye di Rutenio. Nella prima parte sono stati studiati diversi metodi di realizzazione dello starto omogeneo di nanotubi come starto conduttivo della cella. E’ stata proposta la molecola 1-Pyrenemethanol che contiene i gruppi pirenico e ossidrilico, per creare il contatto tra i nanotubi ed il dye. Nella seconda parte del lavoro lo starto di nanotubi e’ stato formato mediante elettroforesi per single-walled nanotubes (SWNTs) e metal-organic chemical vapor deposition (CVD) per multi-walled nanotubes (MWNTs). Entrambi i metodi hanno dato la possibilita’ di creare campioni con ampia area superficiale, dai quali sono state fabbricate le celle solari. Sono state studiate determinate le dipendenze tra i fattori dei metodi e le proprieta’ delle celle prodotte.Item Novel organic optoelectronic materials(2012-11-28) Cospito, Sante; Versace, Carlo; De Simone, Bruna Carla; Bartolino, RobertoIl presente lavoro di Tesi di Dottorato di Ricerca (Scuola di Dottorato in Scienza e Tecnica "Bernardino Telesio") dal titolo "Novel Organic Optoelectronic Materials" è stato svolto all'interno dei laboratori di "Organic Optoelectronic Materials" e "New Syntheses via Organometallic Catalysis" del Dipartimento di Chimica dell'Università della Calabria. Nuovi semiconduttori organici potenzialmente impiegabili in dispositivi optoelettronici quali OLEDs, celle solari, transitors ed elettrocromici sono state progettate, sintetizzate e caratterizzate. La prima parte del lavoro ha riguardato la sintesi e la caratterizzazione di derivati di triarilammine, molecole elettron-donatrici (anodiche), da impiegare in dispositivi elettrocromici ("smart windows") per l'attenuazione della radiazione solare nel vicino infrarosso (NIR). L'intensa ed estesa banda di assorbimento nel NIR prodotta delle specie mono-ossidate ha suggerito l'impiego di queste triarilammine in dispositivi "complementari" in cui vengono utilizzate insieme a molecole elettron-accetrici (catodiche) elettrocromiche nel visibile, per un'ampia modulazione dello spettro solare. Tali sistemi sono stati dispersi all'interno di matrici polimeriche al fine di realizzare dei gel elettrocromici le cui prestazioni sono state ampiamente studiate. La risposta elettrocromica del gel è stata inoltre provata in un dispositivo plastico, dimostrandone le potenziali applicazioni campo dell'elettronica flessibile. La seconda parte del lavoro invece, ha riguardato la sintesi e lo studio delle proprietà di cristalli liquidi semiconduttori di tipo "n" (elettron-accetori) da impiegare in celle solari organiche "bulk heterojunction". Tali molecole, appartenenti alla famiglia dei viologeni estesi, hanno mostrato interessantissime proprietà mesomorfiche fortemente influenzate dalla lunghezza delle catene alchiliche ( a 9, 10 e 11 atomi di carbonio) e dell'anione utilizzato, la bis(triflimmide). Le proprietà elettrochimiche di questi composti sono state investigate sia in soluzione che nelle mesofasi. Un'efficace elettrocromismo dovuta (i) al doppio strato elettrico creato all'elettrodo degli anioni presenti e (ii) all'elevata sovrapposizione degli orbitali di frontiera dell'esteso sistema π- coniugato è stato osservato nelle fasi colonnari e smettiche in cui le molecole si sono auto-assemblate. Infine, le proprietà elettrocromiche di questi composti sono state studiate all'interno di film plastici utilizzabili in dispositivi quali i displays.Item Hybrid nanostructured fillers for polymer electrolytes in the PEM Fuel Cells(2012-11-30) Angjeli, Kristina; Versace, Carlo; Nicotera, Isabella; Bartolino, RobertoThe 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).Item Hydrophilic Ir(III) complexes suitable for the construction of functional mesoporous materials(2012-11-27) Yadav, Yogesh Jivajirao; Versace, Carlo; Ghedini, Mauro; Bartolino, RobertoNowadays, intensive efforts have been carried out on the design of novel advanced molecular materials, which can self-assemble in a strong, directional and reversible way to construct supramolecular materials with specific properties. The rational design and preparation of supramolecular assemblies through the coordination of metal ions with organic ligands has attracted attention for developing novel crystalline materials with interesting structural topologies and promising applications, and has evolved as an interesting research. The metals used in these complexes can serve as structural components and/or as a source of properties (e.g., magnetic, catalytic, optoelectronic, etc). Cyclometallated Ir(III) octahedral complexes possess fascinating properties used in various applications such as luminescent and electrochemiluminescent labeling reagents for biological substrates1, sensors2, or electronic devices3,4. Recently, the interest in ionic Ir(III) complexes is growing rapidly because not only high internal quantum efficiency (~100%) can be achieved in principle, but also tunable emission wavelengths over the entire visible spectrum can be successfully obtained through ingenious modification of ligands. In particular, Ir(III) complexes based on the chelating ligand 2,2’-bipyridine (bpy) have been successfully applied in light-emitting electrochemical cells (LECs) and sensors.5 The theoretically calculated phosphorescence yield (Fp) of the Ir(III) complexes are close to unity in solution.6 The solution investigations have made great contributions to the fundamental understanding of luminescence processes at molecular level. The conclusions drawn from the dilute solution data, however, cannot commonly be extended to the concentrated solutions. Indeed, many Ir(III) complexes show very different light-emitting behaviors in dilute and concentrated solutions and respectively in the solid state. The luminescence is often weakened or quenched at high concentrations, a phenomenon widely known as “concentration quenching”. A main cause for the quenching process is mechanistically associated with the “formation of aggregates”, which is probably why the concentration quenching effect has frequently been referred to as “aggregationcaused quenching” (ACQ). On the other hand “aggregation-induced phosphorescent emission” (AIPE) is an unusual phenomenon existing also in transition metal complexes, which have no emission in solution but enhanced emission in the solid state.7 There are some examples of AIPE, most of them in neutral Ir(III) complexes.8, 9, 10, 11, 12 The main strategies to avoid unpleasant quenching phenomena are based on the dispersion of the chromophore. Mainly, two strategies are employed: engineering at molecular level by introducing functionalities able to electronically disconnect the chromophores (bulky groups or functionalities capable to construct hard crystalline or soft dynamic supramolecular assemblies) or isolating the active molecules in different host matrices (host-guest systems).13 In particular, the dispersion of a chromophore into mesoporous materials not only prevents the aggregation phenomena but also provides increased thermal, chemical and mechanical stability to the final materials. Mesoporous materials are ordered porous materials with periodic distribution of pores, high surface area, controllable large pore sizes in the range of 2 – 50 nm and variable topology of the pores. The inorganic matrixes may be made up of SiO2, TIO2, ZrO2, Al2O3, Nb2O5 etc. Basically, the synthesis of ordered functional mesoporous materials is based on the condensation of an inorganic scaffold on the organised structure formed in water by surfactant molecules. Two different strategies may be employed, the cooperative self-assembly mechanism (CSA) and the true liquid crystal templating’ (TLCT) mechanism.14 The functionalization of the mesoporous material may be done in both cases by inserting the chromophore into the primarily water solution. Therefore, water soluble chromophores may guarantee a better compatibility with the surfactant/water system, whereas a proper functionalization on the molecular structure of the chromophore that permit the self-assembly into supramolecular ordered water assemblies, will allow to use the chromophores directly as structure directing agents (SDAs). Since the photophysical properties of the ionic complexes are influenced profoundly by the surroundings of the molecule both in solution and in condensed states, it is fundamental to study the behavior of such complexes in these different states, in order to achieve a fine tuning of the properties as a function of their structure and order in the final material. The knowledge gained in the assembling of supramolecular materials using non-covalent bonds may be used for the construction of ordered systems in water. This strategy will permit the one-step synthesis of functional mesoporous materials, and to control the order of the final material controlling the order in water of the functional Ir(III) complexes. In particular, the molecular fragments that one can change to achieve the desired properties in the final ionic Ir(III) complexes are the cyclometallating or coordinating ligands, and respectively the counterion. My research therefore is focused on the design and synthesis of hydrophilic ionic Ir(III) complexes with flexible or rigid ancillary ligands and use of different counterions, all suitable for controlling the supramolecular assembly in the solid state, and to transfer the knowledge gained into obtaining ordered structures in water, or water-surfactant systems, necessary for the synthesis of mesoporous materials with defined properties. The ionic octahedral Ir(III) complexes synthesised during this thesis and their classification in different classes are presented in the figure S1Item Behavior and effects of additives in liquid crystal compounds(2011-11-03) Vivacqua, Marco; Bartolino, Roberto; Versace, Carlo; Nicoletta, Fiore P.Item Dense Hyflon® AD membranes for gas separation: influence of the solvent and determination of local free volume(2007-11-30) Macchione, Marialuigia; Longeri, Marcello; Versace, Carlo; Yampolskii, YuriItem Study of composite systems of polymers and liquid crystals with homeotropic orientation(2014-06-24) Gallucci, Maria Caterina; Versace, Carlo; De Filpo, GiovanniItem Synthesis and characterization of new hybrid organic/inorganic materials for electro-optic applications(2014-03-28) Teocoli, Francesca; Ghedini, Mauro; Versace, CarloItem Sintesi e studio di nuovi complessi contenenti Zn(II) e Pd(II) con potenziali proprietà elettroottiche(2014-03-26) Spataro, Tania; Versace, Carlo; Aiello, Iolinda