Dissertations / Theses on the topic 'Electrolytes – Conductivity'

A systematic study of structure-property relations has been carried out on a range of polymers, both with and without mesogenic moieties. These materials have been characterised using various thermal techniques, including DSC and DMTA. These polymers have been complexed with LiClO₄ and the effects of the salt on thermal characteristics have been investigated. In addition, AC impedance spectroscopy has been employed to determine the temperature dependence of the conductivity of these complexes. Results suggest that polymers with mesogenic side groups have the potential to exhibit a conduction mechanism which is independent of both the glass transition temperature of the complex as determined by DSC and the corresponding structural relaxation detected using DMTA. It is found that the glass transition temperature of these materials is determined primarily by the side groups, and not by the polymer backbone. A model is thereby proposed in which ionic motion is decoupled from Tg, but still dependent on the local viscosity of the ionic environment. Appreciable conductivity is therefore observed below the glass transition temperature of the complex, thus resulting in dimensionally stable polymeric complexes with possible applications as solid state electrolytes in batteries.

[Truncated abstract] New, double-doped, Bi2O3-based materials in the Bi2O3 Ln2O3 PbO (Ln = La, Nd, Er and Yb) and Bi2O3 WO3 PbO systems were prepared using solid-state reactions. For the Bi2O3 Er2O3 PbO and Bi2O3 Yb2O3 PbO systems, the air-quenchable compositional domain of the fcc fluorite-type phase was partially established. Temperature dependent conductivity measurements were performed on these quenched-in fluorite-type materials using AC impedance spectroscopy. Conductivity at 750[degrees Celsius] generally increased with increasing Pb2+/Ln3+ and decreasing (Ln3++Pb2+)/Bi3+ ratios. The material (BiO1.5)0.70(ErO1.5)0.15(PbO)0.15 had a conductivity of 0.66 [plus-minus] 0.05 S cm-1 at 750[degrees Celsius], placing it among the most highly conductive Bi2O3-based materials, and was the best new fluorite-type material from a combined conductivity and structural stability viewpoint. Some of the new materials in the Bi2O3 La2O3 PbO and Bi2O3 Nd2O3 PbO systems appeared to have the quenched-in fluorite type structure based on powder X-ray diffraction data. These materials had very high conductivities at 750[degrees Celsius] of `~ 1 S cm-1, but underwent rapid symmetry lowering transformations during heating, thus making them unsuitable for use as solid electrolytes. The fluorite-type structure was not air-quenchable in the Bi2O3 WO3 PbO system, for the compositions synthesised. Room temperature neutron powder diffraction data were collected for quenched-in fluorite-type materials in the (BiO1.5)0.80(LnO1.5)0.20-x(PbO)x, Ln = Er and Yb, x = 0, 0.03, 0.06 and 0.09, and (BiO1.5)0.97-y(ErO1.5)y(PbO)0.03, y = 0.27, 0.17 and 0.12, series. ... This suggests that Pb2+ dopant cations occupy face-centre positions in the fcc unit cell, and the Pb2+ lone pair electrons are likely to be orientated towards an oxide ion vacancy in an adjacent tetrahedral site. Pb2+/oxide ion vacancy interactions affect the migration of oxide ions/oxide ion vacancies through the structure, and are responsible for the significantly larger activation energy for oxide ion migration in the Pb2+-doped materials relative to the Pb2+-free materials. For example, the activation energies of (BiO1.5)0.80(ErO1.5)0.20-x(PbO)x, x = 0.03 and 0.06, were 1.50 [plus-minus] 0.02 and 1.54 [plus-minus] 0.02 eV, respectively, while the activation energy for (BiO1.5)0.80(ErO1.5)0.20 was 1.25 [plus-minus] 0.04 eV. Long-term annealing of the quenched in fluorite-type materials in the Bi2O3 Er2O3 PbO and Bi2O3 Yb2O3 PbO systems at 500 and 600[degrees Celsius] resulted in conductivity lowering structural transformations, making these materials unsuitable for practical use as solid electrolytes at these temperatures. For example, the materials (BiO1.5)0.80(ErO1.5)0.20-x(PbO)x, x = 0.03, 0.06 and 0.09, underwent a fluorite-type to tetragonal transformation during annealing at 500[degrees Celsius] due to <100> oxide ion vacancy ordering, and the rate of conductivity decay at 500[degrees Celsius] increased with increasing Pb2+/Er3+ ratio. Long-term annealing experiments at 500[degrees Celsius] performed on air quenched (Bi2O3)0.705(Er2O3)0.245(WO3)0.050 showed that the disordered fluorite-type structure of this material was not fully stabilised, as evidenced by the presence of superlattice reflections in selected area electron diffraction patterns for the material annealed for 2000 hours, and a gradual conductivity decay after ~ 150 hours annealing.

The thesis details studies relating to polymer electrolytes; the solid ionic conductors farmed by the dissolution of salts in suitable high molecular weight polymers. An outline of polymer electrolyte study is presented with respect to current understanding of the phase behaviour, morphology and conductance behaviour of the electrolyte materials. (In particular, those based upon the linear homopolymer poly(ethylene oxide), PEO.) An electrochemical study has been undertaken (298 K) involving a low molecular weight PEO analogue, PEO(400)e = CH3C02(CH2CH20) CO CH3 (n = 8 - 9 ), containing LiCF3SO3 or LiClO4. The study has shown that at low to medium salt concentrations in polyether media ion - ion interactions are important and are realized as ion association. The conductance vs. concentration behaviour has been modelled according to an equilibrium between single, ion pair and triple ion species where the concentration of simple (single) ions are small and decreasing, and above a total salt concentration of about 0.01 mol kg−1, the majority of the current is carried by triple ion species of the form Li2X- LiX2 (X = CF3SO3 , CIO4). Equilibrium constant data were obtained for single and triple ion formation (from neutral ion pairs). Determination of triple ion formation constants vs. temperature has shown that the triple ion formation process for LiCF3SO3 in PEO(400)e is an exothermic process, negative, whereas for LiClO4 AH = 0 kJinal−1. Using nuclear magnetic resonance (nmr), diffusion coefficients have been obtained for the oligomer chain in PEO(400)e and PEO(400)e.LiCF3SO3 solutions. The chain diffusion coefficients have been shown to give good agreement with those for salt diffusion, determined from conductance measurements via the Nernst - Einstein relation. An in - depth nmr investigation of the PEO.LICF3SO3 system (high molecular weight PEO) has shown that there is partition of lithium environments, probably within the salt rich crystalline phase (EQ/Li - 3.5/1). Significant numbers of lithium nuclei are not observed with the nmr technique because they occupy environments of law symmetry. This was reinforced by other nmr measurements which suggested cation - anion proximity in the crystalline phase. A mixed salt system has been studied, PEO. LiCF3SO3. Nal, and it has been shown that the mixing of salts gave materials with superior conductivities to the relevant single salt systems (PEO. LiCF3SO3 and PEO.Nal) of the same overall salt content. Nmr has shown that the mixed salt effect was due to a larger amorphous (conducting) polymer phase and more potential charge carriers for the mixed salt in comparison to the single salt materials. A marked effect upon lithium motion was observed for PEO.LiCF3SO3 Nal system in comparison to PEO.LiCF3SO3 and it has been proposed that this was due to the observed lithium species becoming mobile at notably lower temperatures for the mixed salt system.

Doutoramento em Nanociências e Nanotecnologia
The main objective of this dissertation is the development and processing of novel ionic conducting ceramic materials for use as electrolytes in proton or oxide-ion conducting solid oxide fuel cells. The research aims to develop new processing routes and/or materials offering superior electrochemical behavior, based on nanometric ceramic oxide powders prepared by mechanochemical processes. Protonic ceramic fuel cells (PCFCs) require electrolyte materials with high proton conductivity at intermediate temperatures, 500-700ºC, such as reported for perovskite zirconate oxides containing alkaline earth metal cations. In the current work, BaZrO3 containing 15 mol% of Y (BZY) was chosen as the base material for further study. Despite offering high bulk proton conductivity the widespread application of this material is limited by its poor sinterability and grain growth. Thus, minor additions of oxides of zinc, phosphorous and boron were studied as possible sintering additives. The introduction of ZnO can produce substantially enhanced densification, compared to the un-doped material, lowering the sintering temperature from 1600ºC to 1300ºC. Thus, the current work discusses the best solid solution mechanism to accommodate this sintering additive. Maximum proton conductivity was shown to be obtained in materials where the Zn additive is intentionally adopted into the base perovskite composition. P2O5 additions were shown to be less effective as a sintering additive. The presence of P2O5 was shown to impair grain growth, despite improving densification of BZY for intermediate concentrations in the range 4 – 8 mol%. Interreaction of BZY with P was also shown to have a highly detrimental effect on its electrical transport properties, decreasing both bulk and grain boundary conductivities. The densification behavior of H3BO3 added BaZrO3 (BZO) shows boron to be a very effective sintering aid. Nonetheless, in the yttrium containing analogue, BaZr0.85Y0.15O3- (BZY) the densification behavior with boron additives was shown to be less successful, yielding impaired levels of densification compared to the plain BZY. This phenomenon was shown to be related to the undesirable formation of barium borate compositions of high melting temperatures. In the last section of the work, the emerging oxide-ion conducting materials, (Ba,Sr)GeO3 doped with K, were studied. Work assessed if these materials could be formed by mechanochemical process and the role of the ionic radius of the alkaline earth metal cation on the crystallographic structure, compositional homogeneity and ionic transport. An abrupt jump in oxide-ion conductivity was shown on increasing operation temperature in both the Sr and Ba analogues.
O principal objetivo deste trabalho é o desenvolvimento e processamento de novos materiais cerâmicos protónicos e iónicos para utilizar como eletrólito das células de combustível de óxidos sólidos (PCFCs e SOFCs, respetivamente). Com este estudo pretende-se, então, desenvolver novas formas de processamento e/ou materiais que apresentem características eletroquímicas atrativas, à base de óxidos cerâmicos nanométricos de pós preparados por processos mecanoquímicos. Existem alguns requisitos que devem ser tidos em conta de forma a garantir a máxima eficiência das PCFCs, destacando-se a elevada condutividade protónica do eletrólito aquando da operação numa gama de temperaturas intermédias, 500-700ºC. Os materiais do tipo “perovskite” foram apresentados como potenciais candidatos a incorporar o eletrólito das PCFCs, sendo o BaZrO3 dopado com 15 mol% de ítrio (BZY) o material base escolhido neste trabalho. Apesar da sua conhecida elevada condutividade protónica, estes materiais apresentam algumas limitações, tais como a fraca sinterabilidade e crescimento de grão. De forma a ultrapassar esta dificuldade, foram adicionadas pequenas quantidades de óxidos de zinco, fósforo e boro que foram estudados como possíveis aditivos de sinterização. A adição de ZnO mostrou melhorias significativas na densificação quando comparado com o material não modificado (BZY), permitindo ainda reduzir a temperatura de sinterização de 1600ºC para 1300ºC. Neste trabalho estudou-se, também, qual o melhor mecanismo de solução sólida para a adição deste aditivo, tendo-se obtido a máxima condutividade protónica nos materiais em que o Zn é intencionalmente introduzido na composição de base de “perovskite”. O P2O5 mostrou ser menos efetivo como aditivo de sinterização. A sua presença foi bastante prejudicial no crescimento de grão, apesar dos elevados níveis de densificação obtidos quando adicionado em quantidades entre 4 e 8 mol%. Porém, a utilização de fósforo mostrou também ser dramática no transporte elétrico, diminuindo a condutividade não só no interior do grão (“bulk”) como nas suas fronteiras. Já a adição de H3BO3 ao BaZrO3 (BZO) mostrou-se muito efetiva para a sinterização deste componente. Contudo, quando adicionado ao sistema dopado com ítria (BaZr0.85Y0.15O3-, BZY), o comportamento é diferente, produzindo níveis deficientes de densificação quando comparado com o BZY puro. Este fenómeno ocorre devido à formação de fases secundárias de borato de bário, cujas temperaturas de fusão são bastante elevadas. Na última parte deste trabalho foi estudado um novo material com condutividade iónica de iões óxido, o (Ba,Sr)GeO3 dopado com K. Neste estudo pretendia-se, não só avaliar a possibilidade de preparar estes pós com recurso a processos mecanoquímicos, como também estudar o papel da variação do raio iónico do catião metálico alcalino-terroso no transporte iónico, homogeneidade composicional e estrutura cristalina. Verificou-se que este material apresenta uma alteração significativa na condutividade iónica com o aumento da temperatura de operação em ambas as composições (Ba e Sr).

Ion transport of electrolytes determines the performance of many electroactive devices, from fuel cells to batteries to soft mechanical actuators. This dissertation aims to address some fundamental issues regarding ion transport of ion dense electrolytes using electrophoretic NMR and NMR diffusometry. I first describe the design and fabrication of the first instrumentation capable of reliable ENMR on highly ion-dense electrolytes such as ionic liquids and electrolytes for zinc-air batteries. I design a new electrophoretic NMR sample cell using parallel capillaries to investigate the electrophoretic mobilities of pure ionic liquids. It shows the first study of a highly ion-dense electrolyte with electrophoretic NMR. Then I employ NMR diffusometry and electrophoretic NMR to investigate ion association of pure ionic liquids. Then I use electrophoretic NMR technique to investigate the electrophoretic mobilities of electrolytes for zinc-air batteries. For Zn2+ salt added dicyanamide (dca) based ionic liquids, I investigate the effects of Zn2+ salt on chemical shift of dca and ion motion. The combination of mobilities measurements and diffusion measurements provides some new insight of ion aggregation. We explore ion transport of ionic liquids inside the ionic polymer Nafion as a function of hydration level. When ionic liquids diffuse inside ionic polymers, isolated anions diffuse faster (e 4X) than cations at high hydration whereas ion associations result in substantially faster cation diffusion (d 3X) at low hydration inside membranes, revealing prevalent anionic aggregates. Finally, we compare diffusion activation energy measurements in a hydrated perfluorosulfonate ionomer and aqueous solutions of triflic acid, which provides insight into water transport dynamics on sub-nm lengthscales. And we explore the physical meaning of activation energy, characterizing local intermolecular interactions that occur on the pre-diffusional (~ 1 ps) timescale.
Ph. D.

In this study, highly ionic conductive solid polymer electrolytes have been prepared by blending high molecular weight polyethylene oxide (PEO: MW 35,000 and 100,000) and bis(trifluoromethane)sulfonamide lithium (LiTFSI) salt. The ionic conductivities were determined for several compositions of the blends at different temperatures. A maximum ionic conductivity of 9.45 x 10-6 S cm-1 at 25 °C has been obtained for the blends containing PEO-35,000/LiTFSI at an ethylene oxide to lithium salt ratio (EO/Li+) of 5, whereas a maximum ionic conductivity 7.7 x 10-6 S cm-1 at 25 °C was observed for the PEO-100,000/LiTFSI blend at EO/Li+ mole ratio of 5. For all the blends, increasing the temperature resulted in enhanced ionic conductivity. Furthermore, addition of tris(pentafluorophenyl)borane (TPFB) increased the conductivities at 25 oC. The overall conclusion of the study is that using LiTFSI and the TPFB in the blends results in ionic conductivities suitable for use in Li-air and/or Li-ion batteries.

Dissertation (Ph. D.)--University of Akron, Dept. of Polymer Engineering, 2007.
"December, 2007." Title from electronic dissertation title page (viewed 01/30/2008) Advisor, Kyonsuku Min; Committee members, Mark Soucek, Kevin A. Cavicchi, Gary R. Hamed, Michael H. Cheung; Department Chair, Sadhan C. Jana; Dean of the College, Stephen Z. D. Cheng; Dean of the Graduate School, George R. Newkome. Includes bibliographical references.

Saving energy in buildings is of great importance because about 30 to 40 % of the energy in the world is used in buildings. An electrochromic window (ECW), which makes it possible to regulate the inflow of visible light and solar energy into buildings, is a promising technology providing a reduction in energy consumption in buildings along with indoor comfort. A polymer electrolyte is positioned at the center of multi-layer structure of an ECW and plays a significant role in the working of the ECW. In this study, polyethyleneimine: lithium (bis(trifluoromethane)sulfonimide (PEI:LiTFSI)-based polymer electrolytes were characterized by using dielectric/impedance spectroscopy, differential scanning calorimetry, viscosity recording, optical spectroscopy, and electrochromic measurements. In the first part of the study, PEI:LiTFSI electrolytes were characterized at various salt concentrations and temperatures. Temperature dependence of viscosity and ionic conductivity of the electrolytes followed Arrhenius behavior. The viscosity was modeled by the Bingham plastic equation. Molar conductivity, glass transition temperature, viscosity, Walden product, and iso-viscosity conductivity analysis showed effects of segmental flexibility, ion pairs, and mobility on the conductivity. A connection between ionic conductivity and ion-pair relaxation was seen by means of (i) the Barton-Nakajima-Namikawa relation, (ii) activation energies of the bulk relaxation, and ionic conduction and (iii) comparing two equivalent circuit models, containing different types of Havriliak-Negami elements, for the bulk response. In the second part, nanocomposite PEI:LiTFSI electrolytes with SiO2, In2O3, and In2O3:Sn (ITO) were examined. Adding SiO2 to the PEI:LiTFSI enhanced the ionic conductivity by an order of magnitude without any degradation of the optical properties. The effect of segmental flexibility and free ion concentration on the conduction in the presence of SiO2 is discussed. The PEI:LiTFSI:ITO electrolytes had high haze-free luminous transmittance and strong near-infrared absorption without diminished ionic conductivity. Ionic conductivity and optical clarity did not deteriorate for the PEI:LiTFSI:In2O3 and the PEI:LiTFSI:SiO2:ITO electrolytes. Finally, propylene carbonate (PC) and ethylene carbonate (EC) were added to PEI:LiTFSI in order to perform electrochromic measurements. ITO and SiO2 were added to the PEI:LiTFSI:PC:EC and to a proprietary electrolyte. The nanocomposite electrolytes were tested for ECWs with the configuration of the ECWs being plastic/ITO/WO3/polymer electrolyte/NiO (or IrO2)/ITO/plastic. It was seen that adding nanoparticles to polymer electrolytes can improve the coloring/bleaching dynamics of the ECWs. From this study, we show that nanocomposite polymer electrolytes can add new functionalities as well as enhancement in ECW applications.

De nouvelles familles de liquides ioniques conducteurs par ion lithium; à anions aromatiques et aliphatiques de type perfluorosulfonate perfluorosulfonylimidure attachés à des oligoéthers (méthoxy polyéthylène glycol mPEG) de longueurs différentes ont été synthétisées et caractérisées dans le but d'améliorer l'interaction entre les chaînes de POE et les sels de lithium en améliorant la mobilité segmentaire. Ainsi différentes membranes amorphes ou peu cristallines améliorent le transport cationique par rapport aux électrolytes polymères usuels. . Leurs propriétés ont été évaluées dans deux types de polymères hôtes : un polyéther linéaire (POE) et un polyéther réticulé préparé par un procédé "VERT". Leurs parties oligooxyéthylène aident à la solvatation des cations lithium et conduisent à l'augmentation des propriétés de transport; c'est à dire la conductivité cationique et le nombre de transport. Leurs stabilités thermiques et électrochimiques sont adaptées à l'application batterie lithium-polymère
The new families of lithium-conducting ionic liquids; aromatic and aliphatic lithium salts based on perfluorosulfonate and perfluorosulfonylimide anions attached to an oligoether (methoxy polyethylene glycol mPEG) with different lengths were synthesized and characterized with the aim to improve the salt interaction with the host polymer's POE chains while keeping a high segmental mobility. They allowed obtaining membranes with lower crystallization degree and higher cationic transport number as compared with benchmarked salts. Their properties as lithium salts were investigated in two types of host polymers i.e. a linear polyether (POE) and a cross-linked polyether prepared by a ‘GREEN' process. Their oligooxyethylene moieties improve the lithium cation solvation leading to an increase in cationic transference numbers. Their electrochemical and thermal stabilities are suitable for lithium battery application

Lowering the operating temperature of the high-temperature, solid oxide fuel cell (SOFC) improves both the thermodynamic efficiency and the lifetime of this energy efficient technology. Unfortunately the rate of oxygen-ion transport through the solid electrolyte is temperature dependent, and materials previously employed as electrolytes in the high-temperature SOFC perform poorly at intermediate temperatures. Therefore new oxygen-ion conductors with enhanced ionic conductivity at intermediate temperatures are required. The bulk of the existing literature on high-temperature SOFCs has focussed on zirconia-based binary systems as electrolytes, due to their high ionic conductivity and negligible electronic conductivity. Only select compositions within the zirconia-scandia system have demonstrated acceptable ionic conductivity levels at intermediate temperatures; however unstable phase assemblage and the high economic cost of scandia are clear disadvantages. Ceria-based binary systems have demonstrated improved oxygen-ion conductivity at intermediate temperature compared to many zirconia systems, however significant levels of n-type electronic conductivity are observed at low oxygen partial pressures. Consequently it was thought unlikely that significant increases in ionic conductivity would be found in existing zirconia- and ceria-based binary systems, therefore another approach was required in an attempt to improve the performance of these established fluorite systems. The fluorite systems Zr0.75Ce0.08M0.17O1.92 (M = Nd, Sm, Gd, Dy, Ho, Y, Er, Yb, Sc) were prepared and investigated as possible, intermediate-temperature SOFC electrolytes in an attempt to combine the higher conductivity found in the ceria systems with the low electronic conductivity observed in the zirconia systems. Also it was anticipated that systems containing dopants not previously observed to confer high ionic conductivity in either zirconia- and ceria-based binary systems, might exhibit enhanced ionic conductivity with expansion of the zirconia lattice resulting from the addition of ceria. All the as-fired Zr0.75Ce0.08M0.17O1.92 compositions possessed the face-centred cubic structure and lattice parameter measurements revealed the anticipated unit cell enlargement as the size of the dopant cation increased. No unusual microstructural parameters were identified that could be expected to interfere with the ionic transport properties in the as-fired compositions. The electrical conductivity was found to be influenced by the dopant-ion radius, the presence of ceria, low oxygen partial pressures and, in some compositions, the formation of poorly conducting, ordered-pyrochlore microdomains dispersed amongst the cubic defect-fluorite matrix. In a second approach to the formulation of new oxygen-ion conductors suitable for the intermediate-temperature SOFC, compounds possessing structures other than the fluorite structure were considered. An examination of the literature for oxides having the pyrochlore, scheelite and perovskite structures showed that the Sr+2- and Mg+2-doped LaGaO3 perovskites (LSGM) possessed ionic conductivity equal to the highest conducting, zirconia and ceria binary compounds. Therefore the perovskite systems La0.9Sr0.1Ga(0.8-x)InxMg0.2O2.85 (X = 0, 0.05, 0.1, 0.2, 0.4, 0.6, 0.8) (I-LSGM) were prepared and examined, the objective being to favourably influence structural parameters believed responsible for optimal ionic conductivity, namely the unit cell symmetry and volume. It was found that In+3 systematically substituted for Ga+3 on to the B-site of LSGM at least up to the X = 0.4 composition. While In+3 was found to replace the Ga+3 as expected, Mg+2, which occupies the same crystallographic site, was also replaced by In+3. Up to the X = 0.2 composition, at least two trace level secondary phases were observed to form along with the bulk I-LSGM phase. For I-LSGM compositions with X > 0.2, significantly larger concentrations of the secondary phases were identified. Evidence of a strontium-rich, high-temperature liquid phase was observed also near the grain boundaries on as-sintered and thermally etched surfaces in LSGM and I-LSGM compositions. It is believed that the observed, high sintered density in the complex, doped-LaGaO3 systems is due to the formation of this high-temperature liquid phase. Increasing levels of diffuse scatter and superstructure formation were observed in electron diffraction patterns in the I-LSGM bulk phase (up to X = 0.2), indicating a possible decrease in vacancy concentration and reduced, localised unit cell symmetry. The electrical conductivity in the I-LSGM compositions was believed to be influenced by the distortion of the oxygen-ion conduction path, a reduction in vacancy concentration, formation of stronger dopant-vacancy associates at low temperature and the presence of ordered structures. In addition, phase instability, in the form of subtle ordering in specific crystalline planes, was observed to influence the electrical conductivity as a function of time at intermediate temperatures.

Polymer electrolyte films based on poly(trimethylene carbonate) (PTMC) mixed with LiTFSI salt in different compositions were synthesized and investigated as electrolytes for lithium ion batteries, where the ionic conductivity is the most interesting material property. Electrochemical impedance spectroscopy (EIS) and DSC were used to measure the ionic conductivity and thermal properties, respectively. Additionally, FTIR and Raman spectroscopy were used to examine ion coordination in the material. Additives of nanosized TiO2 and powders of superionically conducting Li1.3Al0.3Ti1.7(PO4)3 were investigated as enhancers of ionic conductivity, but no positive effect could be shown. The most conductive composition was found at a [Li+]:[carbonate] ratio of 1, corresponding to a salt concentration of 74 percent by weight, which showed an ionic conductivity of 2.0 × 10–6 S cm–1 at 25 °C and 2.2 × 10–5 S cm–1 at 60 °C, whereas for even larger salt concentrations, the mechanical durability of the polymeric material was dramatically reduced, preventing use as a solid electrolyte material. Macroscopic salt crystallization was also observed for these concentrations. Ion coordination to carbonyls on the polymer chain was examined for high salt content compositions with FTIR spectroscopy, where it was found to be relatively similar between the samples, possibly indicating saturation. Moveover, with FTIR, the ion-pairing was found to increase with salt concentration. The ionic conductivity was found to be markedly lower after 7 weeks of aging of the materials with highest salt concentrations.

The synthesis of 2,4,6,8-Tetramethylcyclotetrasiloxane (D4H), and Poly(methylhydrosiloxane) (PMHS) average molecular weight 1700-3200 g/mol, were functionalized with different repeat units of methoxy polyethylene glycol (PEG) (n = 8,12,17). These compounds act as polymer electrolytes with a backbone of siloxane and they were prepared via hydro-silylation reaction to be functionalized with different molecular weights of Ally-PEG. The compounds were confirmed by FT-IR, 1H-NMR and 13C NMR spectroscopy. A hydro-silylation reaction between the functionalized AllyPEG of different molecular weights produced four compounds with a low glass transition temperature that could improve comb like polymer electrolytes conductivity by reducing crystalline phase of PEO. Another way to increase the percentage of the amorphous phase of PEO is to blend it with other polymers. The blending method is considered to be an important method to improve the ionic conductivities and dimensional stability of polymer electrolytes. The main advantages of the blend systems are the simplicity of preparation and the ease to control the physical properties. A high molecular weight of poly 2- vinyl pyridine (Mw=200,000) was added to improve the dimensional stability. Differential scanning calorimetry (DSC) thermal analysis shows that all the blend systems will exhibit an increase in the glass transition temperature by increasing the salt content. The other novel synthesis of polymer electrolytes are triglyme borane and borosilicate. They were synthesized via hydro-boration. These compounds were characterized and confirmed by FT-IR, 1H-NMR 13C NMR spectroscopy. The ionic conductivity of both systems, pure and blend, of different compositions were determined at four temperatures i.e. 25°C, 40°C, 55°C and 70°C. A maximum ionic conductivity value of the siloxane blend is 9.1x10-4 S cm-1 and the pure triglyme borane is 2.14x10-3 S cm-1 at ambient temperature. The ratios of ethylene oxide to lithium salt of siloxane blend and pure triglyme borane were 10:1 and 35:1 respectively. These ratios were the highest conductivity obtained in all the electrolyte systems. The ionic conductivity increases with increasing temperature and salt content to reach optimum concentration. This behavior results in ionic transport, which is supported by the segmental motion of the polymer matrix host.

Blends containing methoxyoligooxyethyleneglycol (MPEGs) (MW 350 and 550) and bis(trifluoromethane)sulfonimide lithium (LiTFSI) salt were prepared by solution blending process using tetrahydrofuran (THF) as a solvent. The ionic conductivity of the blends of different compositions were determined at four temperatures i.e. 25°C, 40°C, 60°C and 70°C. A maximum ionic conductivity value of 3.9x10-3 S cm-1 at 25°C was obtained for the blends containing MPEG-350 at an ethylene oxide to lithium salt ratio of 1:10. The ionic conductivity increases with increasing temperature and shows that the ion transport is aided by the segmental motion of the MPEG chains. 7Li NMR spectroscopy was used to study the nature and dynamics of the salt clusters in the blends

The influence of the structure and elemental composition of lithium ions’ and oxygen vacancies’ (Vo) solid electrolytes (SE) on their electrical properties are investigated in the dissertation. The technological conditions of SE ceramics’ and films’ fabrication, which influence their microstructure, are described. The results of the investigation of the surfaces, temperature stability, and electrical properties are presented. Li+ SE belong to monoclinic, orthorhombic, or rhombohedral symmetries. The microstructure of the ceramics is mainly influenced by the temperature of their sintering. It has been shown by XPS that LiCe2/3PO4 ceramic is Li+-ion conductor. Complex impedance spectroscopy investigation showed that the increase of x in the systems Li1+xScxZr2-x(PO4)3, Li1+xZr2-2xAlxTix(PO4)3, and Li1+xGe2-2xAlxTix(PO4)3 (where x = 0.1, 0.2, 0.3) leads to the increase of bulk ionic conductivity of the ceramics and to the decrease of its activation energy. Phase transition temperature in Li3Sc2–xBx(PO4)3 compounds depends on x. The anomalies of temperature dependencies of bulk conductivity of Li3-xSc2-x-yYyZrx(PO4)3 system were observed when x = 0.1, y = 0, 0.1. The anomalies are related to superionic phase transitions in the materials, but no phase transitions have been detected for x = 0.2 compound in the studied temperature range. Ionic conductivity and its activation energy of YSZ thick films prepared by magnetron sputtering depend on their preparation’s technological... [to full text]
Disertacijoje yra nagrinėjama, kokią įtaką ličio katijonų ir deguonies vakansijų (Vo) kietųjų elektrolitų elektrinėms savybėms daro jų struktūra ir elementinė sudėtis. Darbe yra aprašomos technologinės superjoninių junginių (SJ) keramikų ir sluoksnių gamybos sąlygos, lemiančios jų mikrostruktūrą, bei pateikiami SJ paviršių, temperatūrinio stabilumo ir elektrinių savybių tyrimo rezultatai. Li+ SJ priklauso monoklininei, ortorombinei arba romboedrinei singonijoms. Keramikų mikrostruktūra labiausiai priklauso nuo jų kepinimo temperatūros. LiCe2/3PO4 keramiką paveikus elektriniu lauku, XPS buvo parodyta, kad šioje medžiagoje vyksta Li+ jonų pernaša. Kompleksinės varžos spektroskopijos tyrimai parodė, kad sistemose Li1+xScxZr2-x(PO4)3, Li1+xZr2-2xAlxTix(PO4)3 ir Li1+xGe2-2xAlxTix(PO4)3 (čia x = 0,1, 0,2, 0,3), didinant x, didėja kristalitiniai keramikų laidžiai, o jų aktyvacijos energijos mažėja. Li3Sc2–xBx(PO4)3 junginiuose vykstančio superjoninio fazinio virsmo temperatūra priklauso nuo x. Li3-xSc2-x-yYyZrx(PO4)3 sistemoje kai x = 0,1, y = 0, 0,1 temperatūrinėse kristalitinio laidžio prieklausose yra stebimos anomalijos, susijusios su superjoniniais faziniais virsmais šiose medžiagose, o kai x = 0,2 tirtame temperatūrų intervale faziniai virsmai nevyksta. Magnetroninio dulkinimo metodu suformuotų YSZ storųjų sluoksnių joninis laidis ir šio laidžio aktyvacijos energija priklauso nuo jų paruošimo technologinių sąlygų. Didinant NiO-CGO sluoksnių, suformuotų purškimo pirolizės... [toliau žr. visą tekstą]

Doutoramento em Ciência e Engenharia de Materiais
Condutores protónicos são o cerne funcional de muitos equipamentos de conversão de energia, sensores e controle de luz. Portanto, é muito importante compreender fenómenos interfaciais. O objectivo desta Tese de Doutoramento é o estudo da condutividade protónica de compósitos nano-iónicos obtidos pela dopagem heterogénea de electrólitos fracos com nanopartículas de óxido e materiais mesoporosos, que são essencialmente dieléctricos, através da formação de interfaces condutoras com elevada concentração de protões. Esta investigação baseia-se na dopagem heterogénea de electrólitos fracos tais como imidazol (Iz), benzimidazol (Bz), 1H-1,2,4-triazol (Tz) e pirazol (Pz) com nanopartículas de óxidos metálicos e os correspondentes óxidos mesoporosos, CeO2, TiO2, ZrO2 e BaZrO3. O princípio subjacente é o da criação de zonas de carga espacial com elevada concentração de protões na interface entre o electrólito e o óxido, configurando assim novos tipos de materiais interfaciais do tipo nano-iónico. Numa primeira fase, o trabalho é dedicado à síntese de CeO2, TiO2, ZrO2 e BaZrO3 mesoporosos por nano replicação utilizando SBA-15 ou CMK-3 como moldes. O material molde foi selecionado de forma a minimizar a interacção química entre o molde e os percursores, maximizando assim a pureza da fase de óxido mesoporoso obtido. O óxido de cério foi obtido usando SBA-15, o óxido de zircónio e o óxido de titânio foram preparadas usando ambos os moldes SBA-15 e CMK-3, e o zirconato de bário foi sintetizado unicamente com CMK-3. Numa segunda etapa, medidas de potencial zeta foram usadas para avaliação da carga superficial dos óxidos em contacto com os vários electrólitos, em suspensões aquosas. O potencial zeta diminui com o aumento da fracção do electrólito, o que pode ser explicado assumindo a adsorção selectiva de aniões na superfície dos óxidos. Este efeito é mais evidente com a adição de Iz e Bz do que com a adição de Tz e Pz, em concordância com a menor constante de dissociação apresentada pelos primeiros electrólitos fracos. O enriquecimento dos aniões à superfície tem de ser compensado pelo estabelecimento de regiões de carga ricas em catiões adjacentes à superfície das partículas, o que leva ao desejado efeito mesoscópico do aumento da condutividade. Este efeito foi verificado pelo estudo detalhado de espectroscopia de impedância, o qual mostra que a condutividade protónica, em condições anidras, para os compósitos óxido/electrólito aumenta com o aumento da fracção volúmica das partículas de óxido e com a mesoporosidade. O aumento da condutividade observado pode alcançar cerca de 3 ordens de magnitude em relação a CeO2 e ao electrólito Bz puros. Embora os resultados do aumento da condutividade sejam impressionantes são ainda insuficientes para aplicação tecnológica. Evidências para a contribuição interfacial encontram-se nos espectros de impedância com o aparecimento de semicírculos adicionais, que podem ser correlacionados à área interfacial óxido/electrólito através da fracção volúmica do óxido e da mesoporosidade.
Proton conductors are the functional core of many devices for energy conversion, sensing and light control. Thus, it is very important to understand interfacial phenomena. The main objective of this PhD Thesis is to study the protonic conductivity of nano-ionic composites obtained by heterogeneous doping of weak electrolytes with oxide nanoparticles and mesoporous materials, which are essentially dielectric, via the formation of conducting interfaces with enhanced proton concentration. This investigation is based on the heterogeneous doping of weak proton conducting electrolytes such as imidazole (Iz), benzimidazole (Bz), 1H-1,2,4-triazole (Tz) and pyrazole (Pz) with metal oxide nanoparticles and matching mesoporous counterparts of CeO2, TiO2, ZrO2 and BaZrO3. The underlying principle is the formation of proton-enriched space-charge layers at the electrolyte/particle interface, configuring in this way new types of interfacial materials of nano-ionic type. On a first stage, the work is devoted to the synthesis of mesoporous CeO2, TiO2, ZrO2 and BaZrO3 by nanocasting using suitable SBA-15 silica or CMK-3 carbon hard templates in order to minimize the chemical interaction between the template and the reactant precursors, thus maximizing the phase purity of the obtained mesoporous oxide. Ceria was obtained with SBA-15, zirconia and titania with both SBA-15 and CMK-3, and barium zirconate only with CMK-3. On a second stage, zeta potential measurements were used to assess the oxide surface charge in contact with the various electrolytes, in aqueous suspension. The zeta potential decreases with increasing fraction of electrolyte, which can be explained assuming the selective anion adsorption on the surface of the oxides. This effect is stronger upon addition of Iz and Bz than of Tz and Pz, in agreement with the smaller self-dissociation constants of the former weak electrolytes. The enriched anion surface must be compensated by the establishment of adjacent cation-rich space-charge regions, which produce the desired mesoscopic conductivity enhancement. This effect was verified by detailed impedance spectroscopy studies showing that the proton conductivity in anhydrous conditions of the oxide/electrolyte composites increases with increasing volume fraction of the oxide particle and with the mesoporosity. The observed conductivity enhancement may reach ca. 3 orders of magnitude with respect to pure CeO2 and Bz. While impressive, the attained conductivities are still insufficient for technological application. Evidence for interfacial contribution is found in impedance spectra by additional semicircles, which can be correlated to oxide/electrolyte interfacial area through the oxide volume fraction and mesoporosity.

Made available in DSpace on 2014-10-09T12:37:27Z (GMT). No. of bitstreams: 0
Made available in DSpace on 2014-10-09T14:03:23Z (GMT). No. of bitstreams: 1 02031.pdf: 7939907 bytes, checksum: 472c125a769ddf116f97ea0b005f4340 (MD5)
Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Made available in DSpace on 2014-10-09T12:55:04Z (GMT). No. of bitstreams: 0
Made available in DSpace on 2014-10-09T14:05:55Z (GMT). No. of bitstreams: 0
Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

The thesis is devoted to the field of properties investigation of new types of electrolytes, and assess the appropriateness of electrolytes studied in this paper for use in Li -ion batteries. It focuses specifically on electrolytes based on aprotic solvents and their mixtures with the flame retardants. The goal of the thesis is to investigate the effects of FRAs on electrolyte mixtures via changes in specific conductivity and freezing point. These objectives were fulfilled by using electrochemical impedance spectroscopy in combination with a cryoscopic measurement method. There were overall 16 samples examined. The samples were prepared as a combination of chemicals, specifically Ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), dimethyl sulfone (DMSO2), triethyl phosphate (TEP) Dimethyl methylphosphonate (DMMP), triphenyl phosphate (TPP). Based on the results of the experiments, the mixtures were sorted according to the observed properties in the tables listed in the last part of this paper. These values can be further used to supplement the continuing research of electrolytes and also as assistance in searching for the new electrolyte mixtures.

Disertacijoje yra nagrinėjama, kokią įtaką ličio katijonų ir deguonies vakansijų (Vo) kietųjų elektrolitų elektrinėms savybėms daro jų struktūra ir elementinė sudėtis. Darbe yra aprašomos technologinės superjoninių junginių (SJ) keramikų ir sluoksnių gamybos sąlygos, lemiančios jų mikrostruktūrą, bei pateikiami SJ paviršių, temperatūrinio stabilumo ir elektrinių savybių tyrimo rezultatai. Li+ SJ priklauso monoklininei, ortorombinei arba romboedrinei singonijoms. Keramikų mikrostruktūra labiausiai priklauso nuo jų kepinimo temperatūros. LiCe2/3PO4 keramiką paveikus elektriniu lauku, XPS buvo parodyta, kad šioje medžiagoje vyksta Li+ jonų pernaša. Kompleksinės varžos spektroskopijos tyrimai parodė, kad sistemose Li1+xScxZr2-x(PO4)3, Li1+xZr2-2xAlxTix(PO4)3 ir Li1+xGe2-2xAlxTix(PO4)3 (čia x = 0,1, 0,2, 0,3), didinant x, didėja kristalitiniai keramikų laidžiai, o jų aktyvacijos energijos mažėja. Li3Sc2–xBx(PO4)3 junginiuose vykstančio superjoninio fazinio virsmo temperatūra priklauso nuo x. Li3-xSc2-x-yYyZrx(PO4)3 sistemoje kai x = 0,1, y = 0, 0,1 temperatūrinėse kristalitinio laidžio prieklausose yra stebimos anomalijos, susijusios su superjoniniais faziniais virsmais šiose medžiagose, o kai x = 0,2 tirtame temperatūrų intervale faziniai virsmai nevyksta. Magnetroninio dulkinimo metodu suformuotų YSZ storųjų sluoksnių joninis laidis ir šio laidžio aktyvacijos energija priklauso nuo jų paruošimo technologinių sąlygų. Didinant NiO-CGO sluoksnių, suformuotų purškimo pirolizės... [toliau žr. visą tekstą]
The influence of the structure and elemental composition of lithium ions’ and oxygen vacancies’ (Vo) solid electrolytes (SE) on their electrical properties are investigated in the dissertation. The technological conditions of SE ceramics’ and films’ fabrication, which influence their microstructure, are described. The results of the investigation of the surfaces, temperature stability, and electrical properties are presented. Li+ SE belong to monoclinic, orthorhombic, or rhombohedral symmetries. The microstructure of the ceramics is mainly influenced by the temperature of their sintering. It has been shown by XPS that LiCe2/3PO4 ceramic is Li+-ion conductor. Complex impedance spectroscopy investigation showed that the increase of x in the systems Li1+xScxZr2-x(PO4)3, Li1+xZr2-2xAlxTix(PO4)3, and Li1+xGe2-2xAlxTix(PO4)3 (where x = 0.1, 0.2, 0.3) leads to the increase of bulk ionic conductivity of the ceramics and to the decrease of its activation energy. Phase transition temperature in Li3Sc2–xBx(PO4)3 compounds depends on x. The anomalies of temperature dependencies of bulk conductivity of Li3-xSc2-x-yYyZrx(PO4)3 system were observed when x = 0.1, y = 0, 0.1. The anomalies are related to superionic phase transitions in the materials, but no phase transitions have been detected for x = 0.2 compound in the studied temperature range. Ionic conductivity and its activation energy of YSZ thick films prepared by magnetron sputtering depend on their preparation’s technological... [to full text]

Esta tese apresenta os resultados de estudo de eletrólitos poliméricos obtidos a partir de agar com o propósito de serem aplicados em dispositivos eletrocrômicos (ECDs). Modificações físico-químicas foram efetuadas no agar através da adição do plastificante glicerol, bem como de formaldeído, além da adição de uma fonte de prótons, a partir de ácido acético, ou uma fonte de íons, utilizando-se LiClO4, para promover a condutividade iônica dos filmes. Foram também preparadas blendas a partir de agar com gelatina, com quitosana e com poli(etileno dióxido de tiofeno):poli(estireno) (PEDOT:PSS) com o objetivo de se obter novos materiais alternativos, para serem utilizados como eletrólitos poliméricos. O estudo revelou que todas as membranas apresentaram-se homogêneas, com estabilidade térmica até 200°C e com a estrutura predominantemente amorfa, com valores de temperatura vítrea em torno de -70 °C e transparência no visível de 90%. O manuseio das amostras obtidas revelou boa maleabilidade e aderência ao vidro. Os valores de condutividade iônica das membranas variaram entre 1x10-6 S/cm e 1,1x10-4 S/cm dependendo da composição e quantidade de ácido ou sal de lítio adicionado. No caso das amostras onde foi adicionado PEDOT:PSS, os resultados de condutividade obtidos foram na ordem de 10-4 S/cm, no entanto as amostras apresentaram a transparência somente de 17%. Foi feito um estudo preliminar, de aplicação dos melhores eletrólitos em ECDs revelando mudança de coloração entre o estado colorido e transparente de 25%, reversível inserção de carga entre 11 e 5,0 mC/cm2 e tempo de coloração de 15 segundos e de descoloração de 2 s.
With the aim to develop new electrochromic devices (ECDs), we present a study on polymer electrolytes obtained from agar. Agar was submitted to physicochemical modifications by adding glycerol as plasticizer and formaldehyde; besides, to promote ionic conductivity of the films, a proton source such as acetic acid, or an ion source, LiClO4, were also added. Moreover new alternative materials to be used as polymer electrolytes composed by blends of agar with gelatin, chitosan and poly (ethylene dioxide thiophene):poly(styrene sulfonate) (PEDOT:PSS) were also prepared and characterized. The study revealed that the membranes were homogeneous, with thermal stability up to 200°C and predominantly amorphous. The glass transition values were found to be around -70 °C and the transparency in the visible region of 90%. The ionic conductivity values were in the range of 1x10-6 S/cm to 1.1x10-4 S/cm, depending on composition and amount of added acid or salt. The ionic conductivity of the samples containing PEDOT:PSS were of the order of 10-4 S/cm, however, the corresponding transparencies were found to be about 17%, only. A preliminary study to qualify the performance of our best electrolytes in ECDs have shown a color change of 25%, reversible inserted charge of 5 to 11 mC/cm2 and coloring/bleaching times of 15 and 2 seconds, respectively.

Made available in DSpace on 2014-10-09T12:26:10Z (GMT). No. of bitstreams: 0
Made available in DSpace on 2014-10-09T14:00:18Z (GMT). No. of bitstreams: 0
Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
FAPESP:04/00364-3

Poly(vinyl alcohol) (PVA)-based membranes have gathered significant interest because of their film forming ability and low cost. These films are usually crosslinked to provide a macromolecular network with high dimensional stability. PVA can be modified by introduction of sulfonic acid groups (sPVA) contributing to increase its proton conductivity. In addition, the preparation of hybrid organic-inorganic composite membranes by the addition of graphene oxide (GO) as nano-filler not only reinforces the matrix but also decreases the permeability of solvents. All this has motivated the use of these materials for the preparation of proton exchange membranes (PEMs) for direct methanol fuel cell (DMFC) applications. Contribution I presents the chemical schemes followed for the bi-sulfonation of the PVA, the synthesis of GO and the preparation of PVA/GO and sPVA/GO composite membranes. In addition, a structural, morphological, thermal, and mechanical characterization of the starting materials and the composite membranes were performed. Finally, in order to evaluate the suitability of the prepared PEMs in fuel cells, the prot cond. was evaluated at room temperature. The results showed that the addition of GO (1 wt.%) into the sPVA matrix, 30sPVA/GO membrane, enhance by 89% the prot cond. compared to its homologue membrane, 30sPVA, free-standing of GO. In Contribution II, the proton conductive properties of the previously prepared membranes were investigated as a function of the structural (bi-sulfonation) and morphological (crosslinking and addition of GO) modifications. The bi-sulfonated membrane reinforced with GO, 30sPVA/GO, stands out over the rest. The addition of GO improves considerably its prot cond. (20.96 mS/cm at 90 °C) and its maximum power density (Pmax) in the H2-O2 fuel cell test (13.9 mW/cm2 at 25 ºC). In Contribution III was studied the effect of a new variable, the sufonation of the GO (sGO), on the functional properties of the composites PVA/sGO and sPVA/sGO for DMFC applications. In addition, the results were compared to that obtained for the previously described PVA/GO and sPVA/GO composites. The results conclude that, contrary to expectations, the multiple sulfonation of the 30sPVA/sGO composite strongly reduces the prot cond. (5.22 mS/cm at 50 °C) compared to its homologue 30sPVA/GO (8.42 mS/cm at 50 °C), despite its higher values of ion exchange capacity (IEC). Finally, the 30PVA/sGO composite (1.85 mW/cm2) shows a significant improvement of the DMFC performance (50 °C, 4M methanol solution) compared to the 30sPVA/GO composite (1.00 mW/cm2). The Layer-by-Layer (LbL) assembly method was used in Contribution IV for the preparation of composite membranes assembled via hydrogen bonding interactions. To do this, GO/PVA and GO/sPVA bilayers were deposited on the surface of 15PVA and 15sPVA substrate membranes, respectively. The composites were denoted as 15PVA(GO/PVA)n and 15sPVA(GO/sPVA)n where n is the number of deposited bilayers, in our case n ranges between 1 and 3. Finally, the potential of the composite membranes for DMFC applications were evaluated, showing the best performance the 15sPVA(GO/sPVA)1 composite. Finally, the Contribution V was focused on the preparation of composite membranes by LbL Assembly method, but in this case the assembly forces were electrostatic interactions. The GO was dispersed in a poly(allyl amine hydrochloride) solution (GO-PAH) in order to obtain a positively charged solution. The composites were assembled by alternate deposition of GO-PAH and sPVA layers on the surface of 15PVA and 15sPVA substrates, obtaining as a result the composites 15PVA(GO-PAH/sPVA)n and 15sPVA(GO-PAH/sPVA)n. The best value of prot cond. (8.26 mS/cm at 90 °C) was obtained for the 15PVA(GO-PAH/sPVA)1 composite, almost twice that the value obtained for its homologue sulfonated composite 15sPVA(GO-PAH/sPVA)1 (4.96 mS/cm a 90 °C).
Membranas constituidas básicamente por alcohol polivinílico (PVA) han despertado un gran interés debido a su bajo coste y su fácil procesado para conformarlas en forma de films. Estos films frecuentemente son sometidos a entrecruzamiento para disponer de una red macromolecular con una elevada estabilidad dimensional. La modificación del PVA por introducción de grupos sulfónicos (sPVA) cambia la estructura del polímero contribuyendo a aumentar su conductividad protónica. Además, la preparación de membranas híbridas orgánico-inorgánicas (composites) mediante la adición de óxido de grafeno (GO) refuerza la matriz, a la vez que disminuye su permeabilidad frente a disolventes. Todo ello ha motivado el uso de estos materiales para la preparación de membranas de intercambio protónico (PEMs) empleadas en pilas de combustible de metanol (DMFCs). En la Contribución I se presentan los esquemas químicos conducentes a la bi-sulfonación del PVA, la síntesis del GO y la preparación de las membranas composite PVA/GO y sPVA/GO. Además, se realizó la caracterización estructural, morfológica, térmica y mecánica de cada uno de los materiales de partida y de los composite. Finalmente, con el fin de evaluar su idoneidad como PEMs en pilas de combustible, se evaluó su cond. prot a temperatura ambiente. Los resultados obtenidos mostraron que la adición de GO (1 wt.%) como nano-carga a la matriz de sPVA genera un composite, 30sPVA/GO, cuya cond. prot supera en un 89 % a la de su membrana homóloga sin carga, 30sPVA. La Contribución II trata de explorar las propiedades conductoras de las membranas preparadas previamente en función de la modificación estructural (bi-sulfonación) y la morfológica (reticulación y adición de GO). La membrana bi-sulfonada y reforzada con GO, 30sPVA/GO, destaca sobre el resto. La adición de GO mejora considerablemente tanto la cond. prot (20.96 mS/cm a 90 ºC) como la densidad de potencia máxima (Pmax) en pila de combustible de hidrógeno (13.9 mW/cm2 a temperatura ambiente). En la Contribución III se estudió el efecto de una nueva variable, la sulfonación del GO (sGO), sobre las propiedades funcionales de los composites PVA/sGO y sPVA/sGO en aplicaciones de DMFC. Además, se llevó a cabo un estudio comparativo con los composite PVA/GO y sPVA/GO previamente descritos. Los resultados concluyeron que, en contra a lo esperado, la múltiple sulfonación de la membrana 30sPVA/sGO reduce fuertemente su cond. prot (5.22 mS/cm a 50 ºC) en comparación con su homóloga 30sPVA/GO (8.42 mS/cm a 50 ºC), aun mostrando valores superiores de IEC. Finalmente, el rendimiento de la composite 30PVA/sGO (1.85 mW/cm2) en una DMFC (50 ºC, disolución de metanol 4M) mostró una mejora significativa en comparación con la composite 30sPVA/GO (1.00 mW/cm2). El método de LbL assembly se empleó en la Contribución IV para la preparación de composites ensamblados mediante enlaces por puente de hidrógeno. Para ello, se llevó a cabo la deposición de bicapas de GO/PVA y GO/sPVA sobre los substratos 15PVA y 15sPVA, respectivamente. Los composites se codificaron como 15PVA(GO/PVA)n y 15sPVA(GO/sPVA)n siendo n el número de bicapas depositadas, en nuestro caso n varía entre 1 y 3. Por último, se evaluó su potencial para aplicaciones en DMFC, presentando el mejor comportamiento el composite 15sPVA(GO/sPVA)1. Finalmente, la Contribución V va dedicada a la fabricación de composites mediante el método de LbL Assembly, pero en este caso a través de interacciones electrostáticas. El GO se dispersó en una disolución de hidrocloruro de polialilamina (GO-PAH), con el fin de dotarlo de carga positiva. El ensamblaje se realizó por deposición alterna de capas de GO-PAH y sPVA, obteniéndose los composites 15PVA(GO-PAH/sPVA)n y 15sPVA(GO-PAH/sPVA)n. El mejor valor de cond. prot (8.26 mS/cm a 90 ºC) se obtuvo para el composite 15PVA(GO-PAH/sPVA)1, siendo casi el doble que el obtenido para su homólogo s
Membranes constituïdes a base PVA han despertat un gran interès a causa del seu baix cost i el seu fàcil processament per conformar-les en forma de films. Aquests films freqüentment són sotmesos a entrecreuament per disposar d'una xarxa macromolecular amb una elevada estabilitat dimensional. La modificació del PVA per introducció de grups sulfònics (sPVA) canvia l'estructura del polímer contribuint a augmentar la seua conductivitat protònica. A més, la preparació de membranes híbrides orgànic-inorgànics (composites) mitjançant addició d'òxid de grafè (GO) reforça la matriu, alhora que disminueix la seua permeabilitat enfront de dissolvents. Tot això ha motivat l'ús d'aquestos materials per a la preparació de membranes d'intercanvi protònic (PEMs) emprades en piles de combustible de metanol (DMFCs). En la Contribució I es presenten els esquemes químics conduents a la bi-sulfonació del PVA, la síntesi del GO i la preparació de les membranes composite PVA/GO i sPVA/GO. A més, es va realitzar la caracterització estructural, morfològica, tèrmica i mecànica de cada un dels materials de partida i de les membranes composite. Finalment, per tal d'avaluar la seua idoneïtat com a PEMs en piles de combustible, es va mesurar la seua cond. prot a temperatura ambient. Els resultats obtinguts van mostrar que l¿addició de GO (1 wt.%) com a nano-càrrega en la matriu de sPVA genera un composite, 30sPVA/GO, amb una cond. prot que supera en un 89% a la de la seua membrana homòloga sense càrrega, 30sPVA. La Contribució II tracta d'explorar les propietats conductores de les membranes composite preparades prèviament en funció de la modificació estructural (bi-sulfonació) i morfològica (reticulació i addició de GO). La membrana bi-sulfonada i reforçada amb GO, 30sPVA/GO, destaca sobre la resta. L'addició de GO millora considerablement tant la cond. prot (20.96 mS/cm a 90 ºC) com la densitat de potència màxima (Pmax) a la pila de combustible d'hidrogen (13.9 mW/cm2 a temperatura ambient). En la Contribució III es va estudiar l'efecte d'una nova variable, la sulfonació del GO (sGO), sobre les propietats funcionals dels composites PVA/sGO i sPVA/sGO per aplicacions en DMFC. A més, es va dur a terme un estudi comparatiu amb els composites PVA/GO i sPVA/GO prèviament descrits. Els resultats van concloure que en contra del que s'esperava, la múltiple sulfonació de la membrana 30sPVA/sGO redueix fortament la seua cond. prot (5.22 mS/cm a 50 ºC) en comparació amb la seua homòloga 30sPVA/GO (8.42 mS/cm a 50 ºC), tot i que mostra valors superiors de IEC. Finalment, el rendiment de la membrana 30PVA/sGO (1.85 mW/cm2) en una DMFC (50 ºC, dissolució de metanol 4M) va mostrar una millora significativa en comparació amb la membrana 30sPVA/GO (1.00 mW/cm2). El mètode de LBL assembly es va emprar en la Contribució IV per a la preparació de composites acoblats mitjançant enllaços per pont d'hidrogen. Amb aquest fi, es va dur a terme la deposició de bicapes de GO/PVA i GO/sPVA sobre els substrats 15PVA i 15sPVA, respectivament. Els composites es van codificar com a 15PVA(GO/PVA)n i 15sPVA(GO/sPVA)n on n és el nombre de bicapes dipositades, en el nostre cas n varia entre 1 i 3. Finalment, es va avaluar el seu potencial per a aplicacions en DMFC, presentant el millor comportament el composite 15sPVA(GO/sPVA)1. Finalment, la Contribució V va dedicada a la fabricació de composites mitjançant el mètode de LBL Assembly, però en aquest cas acoblats a través d'interaccions electrostàtiques. El GO es va dispersar en una dissolució de hidroclorur de polialilamina (GO-PAH), per tal de dotar-lo de càrrega positiva. L'acoblament es va realitzar per deposició alterna de capes de GO-PAH i sPVA, obtenint-se els composites 15PVA(GO-PAH/sPVA)n i 15sPVA(GO-PAH/sPVA)n. El millor valor de cond. prot (8.26 mS/cm a 90 ºC) es va obtenir per al composite 15PVA(GO-PAH/sPVA)1, sent gairebé el doble que l'obtingut
Sánchez Ballester, SC. (2017). Synthesis and characterization of new polymer electrolytes to use in fuel cells fed with bio-alcohols [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/86198
TESIS