Simulações computacionais de supercapacitores contendo líquidos iônicos e eletrodos de carbono e MXenes
Data
2023-09-19
Autores
Sampaio, Abner Massari 
Orientadores
Siqueira, Leonardo José Amaral de
Tipo
Tese de doutorado
Título da Revista
ISSN da Revista
Título de Volume
Resumo
Com o intuito de reduzir a dependência dos combustíveis fósseis no consumo energético global, novas fontes de energias alternativas e renováveis têm sido desenvolvidas. Neste contexto, dispositivos capazes de armazenar energia de fontes intermitentes, como energia solar e eólica, têm sido objeto de intenso estudo. Assim, a pesquisa por novos materiais para utilização nestes dispositivos, bem como a compreensão detalhada em nível molecular dos fatores envolvidos no funcionamento dos mesmos, se torna de suma importância. Neste sentido, neste trabalho simulações de dinâmica molecular de líquidos iônicos na interface com modelos de eletrodos de carbono e de MXenes foram realizadas, a fim de avaliar seus desempenhos como supercapacitores. Em eletrodos de grafite, a adição de acetronitrila ao líquido iônico e a consequente diminuição da viscosidade do eletrólito, seguida de um aumento da condutividade iônica, resulta em um aumento da performance do supercapacitor em termos de potência sem que ocorra perda em termos de capacitância. Em eletrodos de grafeno em formato de fendas um modelo de linha de transmissão alimentado com parâmetros obtidos a partir das simulações foi utilizado para descrever a performance dos supercapacitores, evidenciando que o tamanho dos íons tem um papel importante na performance dos dispositivos. Para sistemas contendo modelos de eletrodos de MXenes, duas abordagens para o modelo de potencial constante foram avaliadas. Com o modelo devidamente selecionado, a caracterização estrutural dos eletrólitos, a capacitância, a energia armazenada e os tempos de carregamentos dos eletrodos em eletrodos planos e em formato de fendas, aplicando-se diferentes voltagens, foram avaliados, permitindo a descrição do desempenho dos supercapacitores em relação à energia armazenada e à potência.
In order to reduce dependence on fossil fuels in global energy consumption, new sources of alternative and renewable energy have been developed. In this context, devices capable of storing energy from intermittent sources, such as solar and wind energy, have been the subject of intense study. Thus, the search for new materials for use in these devices, as well as the detailed understanding at the molecular level of the factors involved in their operation, become of paramount importance. In this sense, in this work Molecular Dynamics simulations of ionic liquids at the interface with carbon and MXenes electrode models were performed, in order to evaluate their performance as supercapacitors. In graphite electrodes, the addition of acetonitrile to the ionic liquid and the consequent decrease in the viscosity of the electrolyte, followed by an increase in ionic conductivity, results in an increase in supercapacitor performance in terms of power without loss in capacitance. In slit shaped graphene electrodes a transition line model fed with parameters obtained from simulations was used to describe the supercapacitors performance, showing that the size of the ions plays an important role in the devices performance. For systems with MXene electrode models two approaches of the constant potential model were evaluated. With the model properly selected, the structural characterization of the confined electrolytes, capacitance, stored energy and electrode charging dynamics in both planar and slit shaped electrodes types applying different voltages were calculated, which allows to evaluate the performance of supercapacitors in relation to accumulated energy and power.
In order to reduce dependence on fossil fuels in global energy consumption, new sources of alternative and renewable energy have been developed. In this context, devices capable of storing energy from intermittent sources, such as solar and wind energy, have been the subject of intense study. Thus, the search for new materials for use in these devices, as well as the detailed understanding at the molecular level of the factors involved in their operation, become of paramount importance. In this sense, in this work Molecular Dynamics simulations of ionic liquids at the interface with carbon and MXenes electrode models were performed, in order to evaluate their performance as supercapacitors. In graphite electrodes, the addition of acetonitrile to the ionic liquid and the consequent decrease in the viscosity of the electrolyte, followed by an increase in ionic conductivity, results in an increase in supercapacitor performance in terms of power without loss in capacitance. In slit shaped graphene electrodes a transition line model fed with parameters obtained from simulations was used to describe the supercapacitors performance, showing that the size of the ions plays an important role in the devices performance. For systems with MXene electrode models two approaches of the constant potential model were evaluated. With the model properly selected, the structural characterization of the confined electrolytes, capacitance, stored energy and electrode charging dynamics in both planar and slit shaped electrodes types applying different voltages were calculated, which allows to evaluate the performance of supercapacitors in relation to accumulated energy and power.