The vigorous development of human civilization has significantly increased the energy consumption in recent years. There is a great need to use renewable energy sources to substitute the depleting traditional fossil fuels, such as crude oil, natural gas and coal. The development of low-cost and high-performance energy storage devices (ESDs) and systems have drawn great attention due to their feasibility as backup power supply and their applications in portable electronics and electric vehicles. Supercapacitors are among the most important ESDs because of their long charging-discharging cycle life, high power capability and a large operating temperature range. In this thesis, high-performance activated carbons (ACs)-based SCs have been synthesized from two biomass materials in both “bottom-up” and “top-down” patterns, including high fructose corn syrup and soybean residues, which are economic and environmental friendly. Firstly, a hydrothermal carbonization (HTC) - physical activation method is presented to synthesize activated carbons from high fructose corn syrup (HFCS). The effect of the activation time on the geometrical and porous characteristics of the ACs is investigated. The electrochemical performance of the supercapacitor cells made from AC treated at 850ºC for 4 hours are found as the best with a specific capacitance of 168 F/g at 0.2 A/g in 6 M KOH aqueous system. Secondly, a two-step HTC process followed by a physical activation to prepare activated carbons from soybean residue is presented. The effect of activation temperature on geometrical and porous characteristics of the ACs is studied. The ACs activated at 850ºC are found partly crystallized and exhibit a specific capacitance of 227 F/g at 2 mV/s. To understand the effect of mechanical deformation of the electrode materials on the electrochemical performance of electrical double-layer supercapacitors, a series of compression tests of HFCS-based ACs are further conducted in both dry and wet conditions. The nominal stiffness of the compressed ACs is calculated from the unloading curves. For both dry and wet disks the stiffness get increased with increased compression load, where the wet ones get higher stiffness than that of the dry ones. A simple model of porous materials is used to explain the increase in the stiffness of a compressed disk with the increase of pressure. Lastly, the effect of mechanical deformation on the electrochemical impedance of HFCS-based ACs is studied. When increasing the mechanical pressure from 4 to 81.5 KPa, the system resistance shows a relatively stable trend around 1 ohm, while the charge transfer resistance shows a dramatic dependence on mechanical pressure decreasing from 420 ohms to 1.5 ohms.

Made available in DSpace on 2014-06-11T19:23:11Z (GMT). No. of bitstreams: 0 Previous issue date: 2010-02-26Bitstream added on 2014-06-13T19:50:02Z : No. of bitstreams: 1 tavares_rlm_me_jabo.pdf: 1766165 bytes, checksum: 1586def62988001b88a6b492ab514b0c (MD5) / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / A mineralização da matéria orgânica do solo pode ser compreendida como o processo de degradação de compostos orgânicos por resíduos de culturas e outros materiais orgânicos adicionados no solo. O efeito da mineralização em diferentes ecossistemas e tipos de solos é uma oportunidade para avaliar mudanças nas variáveis microbiológicas e químicas do solo. Nesse trabalho, foi avaliado o efeito da mineralização da matéria orgânica do solo em duas situações: experimento: (1) em diferentes ecossistemas e (2) - em dois solos adicionados de folha e caule de soja. Experimento 1- O objetivo desse trabalho foi quantificar a mineralização da matéria orgânica nos ecossistemas de floresta natural, pastagem e cultura anual na atividade microbiana do solo. As amostras de solo foram coletadas nas áreas de floresta, pastagem e cultura anual (milho), nas profundidades de 0 –10, 10 – 20 e 20 – 40 cm. O carbono da biomassa microbiana (CBM), atividade respiratória microbiana (ARM) e o potencial de nitrificação (PN) foram determinados. Carbono orgânico total (COT), carbono solúvel (CS), ácido húmico (AH) e fúlvico (AF) e a taxa de humificação (TH) e grau de humificação (GH) também foram determinados. O modelo estatístico usado foi o de parcelas subdvididas (fator 1: ecossistemas e fator 2: profundidade) com quatro repetições. No inverno, os teores de COT e CS foram maiores no solo de floresta que no de pastagem e cultura anual de acordo com a ordem: floresta>pastagem>cultura anual e no verão prevaleceu floresta=pastagem>cultura anual. Os teores de AH e AF variaram no inverno e verão de acordo com a ordem floresta>pastagem=cultura anual. O CBM no inverno não foi influenciado pelos ecossistemas e no verão apenas o ecossistema com cultura anual apresentou menor teor de CBM. A ARM foi maior no solo sob pastagem que em solo de floresta e cultura anual, porém... / Soil organic matter mineralization can be understood as a process of degradation of organic compounds from crop residues and other organic material added into the soil. The effect of mineralization in different ecosystems and soil types is an opportunity to assess changes in microbiological and chemical variables of soil. The effect of soil organic matter mineralization was evaluated in two experiments: (1) in different ecosystems; and (2) - in two soils added with leaves and stems of soybean. Experiment 1 – the objective of this study was to quantify the mineralization of organic matter from different ecosystems including natural forest, pasture and annual crop on soil microbial activity. Soil samples were collected from areas of forest, pasture and maize, at depths of 0 -10, 10 - 20 and 20 - 40 cm. The microbial biomass carbon (MBC) contents and the activities of microbial respiratory (MRA), potential nitrification (PN) were determined. Total organic carbon (TOC), dissoLVefd carbon (CS), humic acid (HA) and fulvic (FA) contents and humification rate (TH) and degree of humification (GH) were also determined. The statistical model used was a split plot (factor 1: ecosystem and factor 2: depth) with four replicates. In winter, the TOC and CS contents were higher in the forest soil than in the pasture and annual crop soil and decreased in the following order: forest> pasture> annual crop. in the summer, the relationship was the following: forest =pasture> annual crop. The HA and FA contents varied in winter and summer in the order forest>grassland=annual crop. The CBM content was not influenced by ecosystems in winter and in summer the lowest CBM amount was showed in annual crop. ARM was higher in pasture soil than in forest soil and annual crop, however, the NP was highest in forest soil. The chemical and biological attributes decreased with soil depth, except the rate and degree... (Complete abstract click electronic access below)

Orientador: Ely Nahas / Banca: Wanderley José de Melo / Banca: Brigitte Jonefine Feigh / Resumo: A mineralização da matéria orgânica do solo pode ser compreendida como o processo de degradação de compostos orgânicos por resíduos de culturas e outros materiais orgânicos adicionados no solo. O efeito da mineralização em diferentes ecossistemas e tipos de solos é uma oportunidade para avaliar mudanças nas variáveis microbiológicas e químicas do solo. Nesse trabalho, foi avaliado o efeito da mineralização da matéria orgânica do solo em duas situações: experimento: (1) em diferentes ecossistemas e (2) - em dois solos adicionados de folha e caule de soja. Experimento 1- O objetivo desse trabalho foi quantificar a mineralização da matéria orgânica nos ecossistemas de floresta natural, pastagem e cultura anual na atividade microbiana do solo. As amostras de solo foram coletadas nas áreas de floresta, pastagem e cultura anual (milho), nas profundidades de 0 -10, 10 - 20 e 20 - 40 cm. O carbono da biomassa microbiana (CBM), atividade respiratória microbiana (ARM) e o potencial de nitrificação (PN) foram determinados. Carbono orgânico total (COT), carbono solúvel (CS), ácido húmico (AH) e fúlvico (AF) e a taxa de humificação (TH) e grau de humificação (GH) também foram determinados. O modelo estatístico usado foi o de parcelas subdvididas (fator 1: ecossistemas e fator 2: profundidade) com quatro repetições. No inverno, os teores de COT e CS foram maiores no solo de floresta que no de pastagem e cultura anual de acordo com a ordem: floresta>pastagem>cultura anual e no verão prevaleceu floresta=pastagem>cultura anual. Os teores de AH e AF variaram no inverno e verão de acordo com a ordem floresta>pastagem=cultura anual. O CBM no inverno não foi influenciado pelos ecossistemas e no verão apenas o ecossistema com cultura anual apresentou menor teor de CBM. A ARM foi maior no solo sob pastagem que em solo de floresta e cultura anual, porém... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Soil organic matter mineralization can be understood as a process of degradation of organic compounds from crop residues and other organic material added into the soil. The effect of mineralization in different ecosystems and soil types is an opportunity to assess changes in microbiological and chemical variables of soil. The effect of soil organic matter mineralization was evaluated in two experiments: (1) in different ecosystems; and (2) - in two soils added with leaves and stems of soybean. Experiment 1 - the objective of this study was to quantify the mineralization of organic matter from different ecosystems including natural forest, pasture and annual crop on soil microbial activity. Soil samples were collected from areas of forest, pasture and maize, at depths of 0 -10, 10 - 20 and 20 - 40 cm. The microbial biomass carbon (MBC) contents and the activities of microbial respiratory (MRA), potential nitrification (PN) were determined. Total organic carbon (TOC), dissoLVefd carbon (CS), humic acid (HA) and fulvic (FA) contents and humification rate (TH) and degree of humification (GH) were also determined. The statistical model used was a split plot (factor 1: ecosystem and factor 2: depth) with four replicates. In winter, the TOC and CS contents were higher in the forest soil than in the pasture and annual crop soil and decreased in the following order: forest> pasture> annual crop. in the summer, the relationship was the following: forest =pasture> annual crop. The HA and FA contents varied in winter and summer in the order forest>grassland=annual crop. The CBM content was not influenced by ecosystems in winter and in summer the lowest CBM amount was showed in annual crop. ARM was higher in pasture soil than in forest soil and annual crop, however, the NP was highest in forest soil. The chemical and biological attributes decreased with soil depth, except the rate and degree... (Complete abstract click electronic access below) / Mestre