As the demand for clean and renewable energy sources continues to grow, much attention has been given to solid oxide fuel cells (SOFCs) due to their efficiency and low operating temperature. However, the components of SOFCs must still be improved before commercialization can be reached. Of particular interest is the solid electrolyte, which conducts oxygen ions from the cathode to the anode. Samarium-doped ceria (SDC) is the electrolyte of choice in most SOFCs today, due mostly to its high ionic conductivity at low temperatures. However, the underlying principles that contribute to high ionic conductivity in doped ceria remain unknown, and so it is difficult to improve upon the design of SOFCs. This thesis focuses on identifying the atomistic interactions in SDC which contribute to its favourable performance in the fuel cell. Unfortunately, information as basic as the structure of SDC has not yet been found due to the difficulty in experimentally characterizing and computationally modelling the system. For instance, to evaluate 10.3% SDC, which is close to the 11.1% concentration used in fuel cells, one must investigate 194 trillion configurations, due to the numerous ways of arranging the Sm ions and oxygen vacancies in the simulation cell. As an exhaustive search method is clearly unfeasible, we develop a genetic algorithm (GA) to search the vast potential energy surface for the low-energy configurations, which will be most prevalent in the real material. With the GA, we investigate the structure of SDC for the first time at the DFT+U level of theory. Importantly, we find key differences in our results from prior calculations of this system which used less accurate methods, which demonstrate the importance of accurately modelling the system. Overall, our simulation results of the structure of SDCagree with experimental measurements. We identify the structural significance of defects in the doped ceria lattice which contribute to oxygen ion conductivity. Thus, the structure of SDC found in this work provides a basis for developing better solid electrolytes, which is of significant scientific and technological interest. Following the structure search, we perform an investigation of the electronic properties of SDC, to understand more about the material. Notably, we compare our calculated density of states plot to XPS measurements of pure and reduced SDC. This allows us to parameterize the Hubbard (U) term for Sm, which had not yet been done. Importantly, the DFT+U treatment of the Sm ions also allowed us to observe in our simulations the magnetization of SDC, which was found by experiment. Finally, we also study the SDC surface, with an emphasis on its structural similarities to the bulk. Knowledge of the surface structure is important to be able to understand how fuel oxidation occurs in the fuel cell, as many reaction mechanisms occur on the surface of this porous material. The groundwork for such mechanistic studies is provided in this thesis.

Este trabalho teve como objetivo principal a preparação e caracterização de filmes de alginato de sódio plastificado com glicerol. Foram preparadas amostras de filmes variando-se a concentração de ácido acético ou de perclorato de lítio, com a finalidade de otimizá-los como eletrólitos sólidos poliméricos (ESP) em dispositivos eletroquímicos, como sensores e baterias. Após o preparo dos filmes, estes foram caracterizados por análise elementar (AE), microscopia eletrônica de varredura (MEV), difração de raios-X, termogravimetria (TG), análise térmica mecânico dinâmica (DMTA), espectroscopia no UV-VIS, espectroscopia de infravermelho (IR) e espectroscopia de impedância eletroquímica (EIE). Os filmes preparados com alginato de sódio foram plastificados com 0,6 g de glicerol e apresentaram transparência nos comprimentos de onda da luz visível, boa condutividade iônica e maleabilidade. Através dos difratogramas de raios-X pode-se observar que os filmes possuem predominantemente caráter amorfo. O filme de alginato de sódio dopado com 0,3 mL ácido acético apresentou a melhor condutividade (8,7x10-5 S cm-1 a temperatura ambiente e de 1,15x10-3 S cm-1 a 80°C). Para amostras com quantidades maiores de ácido acético os filmes tornaram-se quebradiços e opacos. Para as amostras preparadas com perclorato de lítio a melhor condutividade obtida foi com o filme preparado utilizando 15% em massa de perclorato de lítio: 3,1x10-4 S cm-1 a temperatura ambiente e 1,2x10-3 S cm-1, a 80°C. As análises dos valores de condutividade em função da temperatura das amostras de alginato de sódio revelaram que este segue o modelo Vogel-Tamman-Fulcher (VTF) de condução, onde a movimentação das cadeias poliméricas auxilia na condução iônica. O valor de energia de ativação foi de 36,14 kJ mol-1 para a amostra com 0,3 mL de ácido acético foi de 36 kJ mol-1 para a amostra com 0,4 mL de ácido. Para os filmes preparados com 15% em massa de perclorato de lítio foi de 18,43 kJ mol-1. Essas novas membranas demonstraram ser candidata promissora para aplicação em diversos dispositivos eletroquímicos. / The aim of this study was the preparation and characterization of sodium alginate membranes plasticized with glycerol. The samples were obtained with different concentration of acetic acid or lithium perchlorate in order to use them as solid polymer electrolytes (SPE) in electrochemical devices, such as sensors and batteries. The films were characterized by elemental analysis (EA), scanning electron microscopy (SEM), X-ray, thermogravimetry (TG), dynamic-mechanical thermal analysis (DMTA), UV-visible spectroscopy, infrared spectroscopy (IR) and electrochemical impedance spectroscopy (IES). The samples plasticized with 0.6 g of glycerol showed good transparency, good ionic conductivity and flexibility. X-ray diffractograms evidenced predominantly amorphous state of the samples. The best ionic conductivity results of 8.7 x 10 -5 S cm -1 at room temperature and 1.15 x 10 - 3 S cm -1 at 80 ° C were obtained with sodium alginate samples containing 0.3 mL of acetic acid. Samples with larger amounts of acid became brittle and opaque. The best conductivity values of 3.1 x10 -4 S cm -1 at room temperature and 1, 2 x10 -3 S cm -1 at 80 ° C were obtained for the samples containing 15 wt.% of lithium perchlorate.. The analysis of the conductivity as a function of temperature revealed that they follow the Vogel-Tamman-Fulcher (VTF) conductivity model. The activation energy were 36, 14 kJ mol -1 for the sample with 0.3 mL of acetic acid and 36 kJ mol -1 for the sample with 0.4 mL of acid. The sample with 15 wt.% of lithium perchlorate showed activation energy of 18.43 kJ mol -1. This new ionic conducting membranes are good candidates to be used as electrolytes in electrochemical devices.

Thesis (MSc. Agriculture (Horticulture)) -- University of Limpopo, 2016 / The Agricultural Research Council-Institute for Tropical and Subtropical Crops (ARC-ITSC) is continuously developing new avocado selections, in order for the South African Avocado Industry (SAAI) to remain competitive in various international avocado markets. However, information on the response of some of these selections, including ‘Fuerte 2 and 4’, ‘BL1058’ and ‘H287’ to low temperature storage and ripening physiology, has not been investigated. Thus, the objective of this study was to evaluate the effect of harvest season and ripening duration on the physico-chemical properties of newly developed ‘Fuerte-type’ avocado fruit selections during ripening. ‘Fuerte-type’ avocado fruit were indexed for maturity using moisture content, thereafter harvested and stored at 5.5°C for 28 days during the 2014 and 2015 harvest seasons. The experiment comprised five treatments: control (commercial ‘Fuerte’), ‘Fuerte 2 and 4’, ‘BL1058’ and ‘H287’ arranged as a factorial in a completely randomised design (RCD) with 3 replicates. The treatment factors were: (i) 2 x harvest seasons, (ii) 5 x selections and (iii) 6 x ripening days. After withdrawal from low storage temperature, fruit were ripened at ambient temperature. During ripening, the following physico-chemical properties were evaluated; external chilling injury, electrolyte leakage, mass loss, firmness, respiration rate and peel colour. Results showed that selections and harvest seasons had no significant effect (P=0.668) on the moisture content of the evaluated ‘Fuerte-type’ avocado fruit. After withdrawal from low storage temperature, there was a significant interaction (P˂0.05) between selections and harvest seasons on external chilling injury and electrolyte leakage. Results further showed that external chilling injury correlated with electrolyte leakage during both harvest seasons. Treatment factors had no significant effect (P=0.997) on mass loss. Similarly, treatment factors had no significant effect (P=0.139) on firmness. However, selection ‘H287’ had hard skin with an average firmness of 83.44 densimeter units during ripening in both harvest seasons. Treatment factors were highly significant (P˂0.05) on respiration rate. Respiration rate followed a climacteric pattern and the magnitude of climacteric peak and day of occurrence varied amongst selections during both harvest seasons. Ripening percentage differed significantly (P˂0.05) amongst harvest seasons, selections and ripening days. Treatment factors had no significant effect on lightness (P=0.711), chroma (P=0.378) and hue angle (P=0.536) skin colour parameters,however, variations were recorded as a result of the cold damage black spots. The results indicated that the ‘Fuerte-type’ avocado selections had poor storage qualities. Further studies are required to evaluate physico-chemical properties during low storage temperature and the effect of season, production conditions and maturity level on development of chilling injury. In addition, studies on application of treatments to reduce chilling injury symptoms and analysis of bioactive compounds should be considered for conclusive recommendations. Thereafter, the selections can be planted in different production regions to assess and select the best producing and quality combinations for a given region as part of phase III of the project / Agricultural Sector Education Training Authority (AgriSeta) and National Research Foundation (NRF)

Dissertation thesis is focused on study of liquid electrolytes for lithium ion batteries. The electrical and physical properties of aprotic electrolytes are observed. The main goal is to increase the fire safety of the batteries. An anhydrous solvents and there blends was investigated. The common used solvents mixtures and new low flammable solvents were used. The common used solvents were used propylene carbonate, ethylene carbonate and others. The new solvents were sulfolane and dimethyl sulfone. In the second part of the work the phosphor base flame retardants as additive in electrolytes was investigated. The last part deals with ionic liquids and there possible use as electrolyte in lithium ion batteries.

This work deals with electrolytic conductivity of gel polymer electrolytes. In the theoretical part of the work the methacrylates, the polymerization and the basic outlines of gel polymer electrolytes conductivity are described. The preparation and electrical conductivity of gels based on PMMA are described in the experimental part.

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Due to the successful commercialization of lithium-ion batteries (LIBs), there is a growing interest in developing new battery materials with beneficial electrochemical properties. However, the uneven distribution of lithium resources and the low abundance of lithium in the earth crust are the main obstacles for further development and large-scale production of LIBs. Sodium-ion batteries (SIBs), an alternative that can partly meet the energy storage challenges, are getting attentions of researchers due to the wide availability and lower cost of sodium resources. Nevertheless, the conventional liquid electrolytes of either LIBs or SIBs composed of fluorinated salts dissolved in volatile organic solvents, posing serious safety issues due to the instability of the salts and flammability of the solvents. There is an urge to develop new fluorine-free electrolytes with improved physicochemical and electrochemical properties. In this context, the conventional fluorinated salts should be replaced with fluorine-free salts and the flammable solvents should be substituted with non-flammable solvents. There are a number of strategies to develop high-performant electrolytes including ambient-temperature ionic liquids (ILs), organic ionic plastic crystals (OIPCs) and highly concentrated electrolytes (HCEs) utilizing new salts and solvents. In this thesis, novel phosphorus-based ionic materials and electrolytes are introduced and their properties are thoroughly investigated. In the first part (Paper I), fluorine-free NaDEEP salt and TEOP solvent are employed to make “solvent-in-salt” (SIS) sodium electrolytes, also known as HCEs. Unexpectedly, the addition of TEOP solvent lead to an increase in the oxidation stability of the SIS electrolytes. In addition, an unusual ionic conductivity behavior is found – the ionic conductivities of Na electrolytes increase with increasing salt concentration. The “salt-rich” and “solvent-rich” phases formed within the electrolytes are investigated using multinuclear liquid-state NMR spectroscopy and NMR diffusometry. In the second part (Paper II), a series of orthoborate-based ionic materials, specifically OIPCs, containing phosphonium/ammonium cations are prepared to compare with the popular fluorine-free, bis(oxalato)borate (BOB) salts. The tetrabutyl phosphonium bis(glycolato)borate ([P4444][BGB]) OIPC displays much higher decomposition temperature than the structural analogous [P4444][BOB] IL. The crystal structures of LiBGB and NaBGB salts are resolved using single-crystal X-ray diffraction analysis. Unlike LiBOB, the BGB-based salts revealed excellent moisture stability over an extended time of up to 8-weeks air exposure. Multinuclear solid-state NMR spectroscopy indicates weaker cation-anion interactions in phosphonium-based salts than the ammonium-based ones. Finally, in the third part (Paper III), two-component and three-component eutectic electrolytes, composed of pyrrolidinium saccharin (PySc), lithium saccharin (LiSc) and/or [P4444][BGB] salt. The resulting mixtures showed significantly lower melting temperatures than the neat salts. The physicochemical and thermal properties of these salts are thoroughly investigated and discussed.

The threat of the ongoing climate crisis requires the complete reduction of carbon emissions in the next two to three decades. Carbon dioxide electrochemical reduction (CO₂ER) poses a promising pathway to be able to maintain our current energy infrastructures in a carbon neutral fashion, by allowing the production of fuels and chemicals, such as CO, methanol and ethylene, with the use of carbon capture technologies and green energy. Thus far, Cu is the only metal that has demonstrated the ability to form hydrocarbon products. However, Cu is hindered by low selectivity. Improvements have been observed by coupling Cu with noble metals, such as Ag and Au. However, despite significant advancements, the technology has yet to achieve sufficient performance in activity, stability and selectivity for commercial viability. As such, this work pursued to further advance the activity of CO₂ER through the use of plasmonic Cu-based catalysts and the study of novel dinitrile-based electrolytes. It has recently been identified that CO₂ER can benefit from direct plasmonic effects induced by light illumination. In essence, certain light wavelengths can induce collective oscillations of the free electrons in the metallic particles, leading to an enhancement of their electrocatalytic performance. As such, the first project of this work involved the development and testing of plasmonic Cu-Ag bimetallic catalysts for the application of CO₂ER. Cu, Ag, as well as Cu-Ag bimetallic particles with variable morphologies were able to be synthesized through a facile one-pot sodium borohydride chemical reduction method. The synthesized catalyst performance was also compared to commercial catalysts. The synthesized particles were found to be active catalysts for CO₂ER, with improved electro-catalytic activities exhibited by Cu₈₅Ag₁₅, Cu₆₀Ag₄₀ and Cu syntheses in respective order. All nanoparticles demonstrated increases in the catalytic activity ranging between 15-26% under white light illumination, attributed to plasmonic promotion. The best plasmonic promotion of 26% was observed in the CuAg commercial alloy. Meanwhile, the best promotion of the synthesized bimetallic particles was of 18% found in the Cu₆₀Ag₄₀ catalyst. Additionally, improved electrochemical and plasmonic stability was observed with the use of the Cu-Ag bimetallic synthesized structures compared to monometallic Cu. In addition, most studies pertaining CO₂ER involve aqueous electrolytes due to their low cost and low toxicity. However, these systems are hindered by mass transfer limitations due to the low solubility of CO₂ in water. Organic-based electrolytes have been subjects of research as they possess higher CO₂ solubilities to water. As dinitriles pose a novelty in the role of CO₂ER, dinitrile-based electrolytes were studied and tested for the application. It was hypothesized that due to the decreased polarity in dinitrile solvents, CO₂ concentrations in the electrolyte would increase leading to improved catalytic activity. The testing was conducted by evaluating and comparing acetonitrile (ACN), adiponitrile (ADN) and sebaconitrile (SBN) solvent-based electrolytes. Increased CO₂ solubility was observed in the dinitriles with 582 mM and 503 mM of dissolved CO₂ in ADN and SBN respectively, compared to 270 mM in ACN. Results were corroborated through DFT modelling, indicating preference of CO₂ absorbance to nitrile groups on the molecules. However, despite increases in CO₂ concentration, the electrochemical activity decreased from ACN > ADN > SBN. The trend in activity was observed to be inversely proportional to the viscosity of the dinitrile solvents, which affected the ionic conductivity. Based on these developments, the present thesis opens a new perspective for the use of Cu-based nanoparticles for direct plasmonic enhancement with the use of a broad-range wavelength white light. Furthermore, the work also sheds light on the properties and resulting electrocatalytic activities of the use of dinitrile organic electrolytes for CO₂ER. The presented findings provide significant groundwork for further developments in the realm of CO₂ER.

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