Esta dissertação apresenta a caracterização e o preparo de filmes a partir de amido de mandioca nativo e modificado industrialmente (amido acetilado e amido oxidado - acetilado), através da plastificação com glicerol , sorbitol ou etileno glicol. Estes filmes foram preparados adicionando-se um sal (perclorato de lítio) com o propósito de serem utilizados como eletrólitos sólidos poliméricos (ESP), os quais apresentam grande potencial de aplicação em dispositivos eletrocrômicos, sensores e baterias, por isso os ESPs devem ser: transparentes, apresentar boa aderência e maleabilidade além de boa condutividade iônica. As modificações conferidas ao amido foram estudadas empregando-se técnicas caracterização por espectroscopia no infravermelho, RMN e análise elementar. A distribuição de massa molecular das amostras de amido nativo e dos amidos modificados também foi estudada através da técnica de cromatografia de permeação em gel (GPC). Os filmes foram preparados utilizando-se diferentes proporções de plastificante e de sal e em seguida com intuito de efetuar as caracterizações físico-químicas estas amostras foram submetidas à análises de espectroscopia de impedância eletroquímica, difração de Raios-X, Microscopia Eletrônica de Varredura (MEV), análises espectrofotométricas de UV-visível, além das análises térmicas (TG e DSC). / This dissertation presents the preparation and characterization of films obtained from native and industrially modified (acetilate and oxidate-acetilate), cassava starches, through the plasticization with glycerol, sorbitol or ethylene glycol. These films are prepared adding a salt (lithium perchlorate) so that they can be used as solid polymeric electrolytes (ESP), which present great application potential in electrochromic devices, sensors and batteries, therefore the films obtained must be transparent, present good adherence and flexibility besides good ionic conductivity. The modifications of the starch were studied using techniques of characterization by infrared espectroscopy, RMN and elementary analysis. The distribution of the molecular mass of the samples of native and modified starches was also studied by means of gel permeation chromatography (GPC). The films were prepared using different proportions of plasticizers and salt. For the physical-chemical characterization of the samples, they were subjected to analyses of electrochemical impedance spectroscopy, X-Ray diffraction, Scanning Electronic Microscopy (SEM), Uv-visible spectroscopy, besides thermal analyses (TG and DSC).

Neste trabalho foi proposto investigar as características de capacitores eletroquímicos de dupla camada elétrica (supercapacitores) utilizando como matéria prima um eletrólito biocompatível como rota viável de baixo custo econômico para obtenção de dispositivos eletrônicos para armazenamento de energia. O objetivo principal foi estudar a influência dos vários parâmetros de processamento nas características elétricas de supercapacitores à base de eletrólito neutro, utilizando, na preparação dos eletrodos oxido de grafeno reduzido via HDDR 400°C e o carbono ativado, também com baixa toxidade e impacto ambiental. O primeiro tópico consistiu na preparação de eletrólitos com diferentes concentrações para avaliar este parâmetro na curva de autodescarga dos supercapacitores. Alternativamente realizou-se a caracterização dos eletrodos preparados com oxido de grafeno reduzido via HDDR 400°C e carbono ativado por ensaios de voltametria cíclica em um analisador eletrônico computadorizado de supercapacitores, que resultou na determinação da capacitância específica do material precursor e das resistências internas. Foram utilizadas técnicas adicionais para caracterização dos materiais precursores e processados, tais como: microscopia eletrônica de varredura (MEV-EDS), difração de raios-X (DRX). / On this work was proposed research the electrochemical double layer capacitors characteristics (supercapacitors) using an environmentally compatible electrolyte as viable low economic cost path to obtain electronics devices for energy storage. The mains objective was to study the influence of the various processing parameters on electrical characteristics of supercapacitors based in neutral electrolyte, using in the preparation the activated carbon and reduced graphene oxide HDDR 400°C, also with low toxicity and environmentally impact. The first topic consisted in the preparation of electrolytes with different concentrations to evaluate this parameter in the self-discharge curve of supercapacitors. Alternatively was made characterization experiments of the activated carbon electrodes and rGO HDDR 400°C by cyclic voltammetry essays in an electronic computerized analyzer of supercapacitors that resulted in the determination of the precursor material specific capacitance and internal resistances Was utilized additional technics for characterization of precursor materials such as scanning electron microscopy (MEV-EDX) and X-ray diffraction (DRX).

Tese de doutoramento. Engenharia Química e Biológica. Faculdade de Engenharia. Universidade do Porto. 2009

In this work the use of the solid acid CsHSO4 as an electrolyte in a hydrogen/oxygen fuel cell or the disassociation of water into hydrogen and oxygen has been investigated. Several issues have been cited in literature regarding the use of CsHSO4 as a solid electrolyte; these include: difficulty interpreting proton conductivity profiles of real membranes, high permeability of the membrane to fuel and product gases, and low mechanical strength. In an attempt to improve our understanding and possibly eliminate these issues, performance characteristics of prepared CsHSO4 membranes have been investigated utilizing various methods of synthesis and membrane fabrication. A consistent method of CsHSO4 membrane construction was developed based on these investigations. In addition, a novel method of sintering to decrease the membrane's permeability to fuel gases was developed and evaluated. The effects of these measures were investigated and tested in a prototype cell for proof of concept of fuel cell and electrolysis applications.

Supercapacitors are one of the most important electrochemical energy storage and conversion devices, however low ionic conductivity of solid state polymer electrolytes and the poor accessibility of the ions to the active sites in the porous electrode will cause low performance for all-solid-state supercapacitors and will limit their application. The objective of the dissertation is to improve the performance of all-solid-state supercapactor by improving electrolyte conductivity and solving accessibility problem of the ions to the active sites. The low ionic conductivity (10-8 S/cm) of poly(ethylene oxide) (PEO) limits its application as an electrolyte. Since PEO is a semicrystal polymer and the ion conduction take place mainly in the amorphous regions of the PEO/Lithium salt complex, improvements in the percentage of amorphous phase in PEO or increasing the charge carrier concentration and mobility could increase the ionic conductivity of PEO electrolyte. Hot pressing along with the additions of different lithium salts, inorganic fillers and plasticizers were applied to improve the ionic conductivity of PEO polymer electrolytes. Four electrode methods were used to evaluate the conductivity of PEO based polymer electrolytes. Results show that adding certain lithium salts, inorganic fillers, and plasticizers could improve the ionic conductivity of PEO electrolytes up 10-4 S/cm. Further hot pressing treatment could improve the ionic conductivity of PEO electrolytes up to 10-3 S/cm. The conductivity improvement after hot pressing treatment is elucidated as that the spherulite crystal phase is convert into the fringed micelle crystal phase or the amorphous phase of PEO electrolytes. PEO electrolytes were added into active carbon as a binder and an ion conductor, so as to provide electrodes with not only ion conduction, but also the accessibility of ion to the active sites of electrodes. The NaI/I2 mediator was added to improve the conductivity of PEO electrolyte and provide pseudocapacitance for all-solid-state supercapacitors. Impedance, cyclic voltammetry, and gavalnostatic charge/discharge measurements were conducted to evaluate the electrochemical performance of PEO polymer electrolytes based all-solid-state supercapacitors. Results demonstrate that the conductivity of PEO electrolyte could be improved to 0.1 S/cm with a mediator concentration of 50wt%. A high conductivity in the PEO electrolyte with mediator is an indication of a high electron exchange rate between the mediator and mediator. The high electron exchange rates at mediator carbon interface and between mediator and mediator are essential in order to obtain a high response rate and high power. This automatically solves the accessibility problem. With the addition of NaI/I2 mediator, the specific capacitance increased more than 30 folds, specific power increased almost 20 folds, and specific energy increased around 10 folds. Further addition of filler to the electrodes along with the mediator could double the specific capacitor and specific power of the all-solid-state supercapacitor. The stability of the corresponded supercapacitor is good within 2000 cycles.

No description available.

Dry bean (Phaseolus vulgaris) is a sub-tropical crop severely affected by exposure to low temperatures during all of its growing stages. Cool spring temperatures and the risk of frost are major limiting factors for the early sowing of dry bean in Saskatchewan. Due to its economic importance; however, it has been introduced to Saskatchewan, but it needs to be made more cold tolerant to further expand acreage. The genes that can contribute some tolerance to low temperature stress in bean are not found within the primary gene pool, which limits the capability of breeders to generate a cultivar with such characteristics. Consequently studies have being done in order to find a possible source of genes that can induce tolerance to low temperature exposure. Phaseolus acutifolius is a relative of the domesticated dry bean and previous hybridizations with it have been successful. It is also known to be tolerant to abiotic stresses such as drought. For this reason the decision was taken to explore the level of resistance to low temperature stress exposure in several P. acutifolius accessions. Using whole plant freezing tests in controlled environment chambers, P. acutifolius W6 15578 was found to be more tolerant to exposure to sub-zero temperatures than were P. vulgaris genotypes. Interspecies hybrids were produced between P. vulgaris NY5-161 and W6 15578 and BC2 plants were produced using embryo rescue. The whole plant freezing test is a destructive method that cannot be used with unique F1 and BC2 genotypes, so an alternative methodology to evaluate the hybrids was explored. An electrolyte leakage test was used and showed similar results to the whole plant freezing test with the parent plant controls. The F1 hybrids had an intermediate tolerance to low temperature stress and the further generations (BC1 and BC2) had a better level of tolerance to this kind of stress than the cultivated parent (NY5-161). This suggests that the genes that confer tolerance to low temperature exposure are being maintained through several generations of backcrossing and that these interspecies hybrids may offer a chance for the development of improved dry bean cultivars for the Saskatchewan environment.

The development of improved water management strategies for the polymer electrolyte membrane fuel cell (PEMFC) could stand to benefit from an improved understanding of the surface and internal structure of the gas diffusion layer (GDL). The GDL is a fibrous porous material enabling mass transport between the PEMFC catalyst layer and flow fields. Fluorescence-based visualizations of liquid water droplet evaporation on GDL surfaces were performed to investigate water droplet pinning behaviours. The heterogeneous in-plane and through-plane porosity distributions of untreated GDLs were studied using computed tomography visualizations. The through-plane porosity distributions were utilized to calculate heterogeneous local tortuosity, relative diffusivity, and permeability distributions. Finally, the heterogeneous through-plane porosity distributions of GDLs treated for increased hydrophobicity were investigated. This work provides new insight into GDL material properties to better inform future PEMFC models.

The development of improved water management strategies for the polymer electrolyte membrane fuel cell (PEMFC) could stand to benefit from an improved understanding of the surface and internal structure of the gas diffusion layer (GDL). The GDL is a fibrous porous material enabling mass transport between the PEMFC catalyst layer and flow fields. Fluorescence-based visualizations of liquid water droplet evaporation on GDL surfaces were performed to investigate water droplet pinning behaviours. The heterogeneous in-plane and through-plane porosity distributions of untreated GDLs were studied using computed tomography visualizations. The through-plane porosity distributions were utilized to calculate heterogeneous local tortuosity, relative diffusivity, and permeability distributions. Finally, the heterogeneous through-plane porosity distributions of GDLs treated for increased hydrophobicity were investigated. This work provides new insight into GDL material properties to better inform future PEMFC models.

The anisotropic mass transport issues inside a fuel cell membrane have been studied in this thesis using computer modelling. The polymer electrolyte membrane (PEM) conductivity of a PEM fuel cell (PEMFC) depends on the hydration state of the hydrophilic charged sites distributed in the pores of the membrane. Water humidification of these charged sites is crucial for sustaining the membrane conductivity and reducing concerning voltage losses of the cell. During the operation of a PEMFC, the transport of humidified inlet gases (fuel/oxidant) is influenced by external design factors such as flow field plate geometry of the gas circulating channels. As a result, there arises a distribution in the mass transport of water inside the membrane electrode assembly. A two-dimensional, cross-the-channel, fuel cell membrane layer mass transport model, developed in this work, helps the study of the impact of factors causing the distribution in the membrane ionic conductivity on ohmic losses.<p>The governing equations of the membrane mathematical model stem from the multicomponent framework of concentrated solution theory. All mass transport driving forces within the vapour and/or liquid equilibrated phases have been accounted in this research. A computational model, based on the finite control volume method, has been implemented using a line-by-line approach for solving the dependent variables of the mass transport equations in the two-dimensional membrane domain. The required boundary conditions for performing the anisotropic mass transport analysis have been obtained from a detailed agglomerate model of the cathode catalyst layer available in the literature.<p>The results obtained using boundary conditions with various flow field plate channel-land configurations revealed that the anisotropic water transport in the cathode half-cell severely affects the ohmic losses within the membrane. A partially humidified vapour equilibrated membrane simulation results show that a smaller channel-land ratio (1:1) sustains a better membrane performance compared to that with a larger one (2:1 or 4:1). Resistance calculations using the computer model revealed that ohmic losses across the membrane also depend on its physical parameters such as thickness. It was observed that the resistance offered by a thinner membrane towards vapour phase mass transport is comparatively lower than that offered by a thicker membrane. A further analysis accounting the practical aspects such as membrane swelling constraints, imposed by design limitations of a fuel cell, revealed that the membrane water content and ionic conductivity are altered with an increase in the compression constraint effects acting upon a free swelling membrane.