Simulação de materiais com propriedades metálicas em eletrólitos
Data
2022-11-24
Autores
Silva, Isabel Amaral da 
Orientadores
Siqueira, Leonardo José Amaral de
Tipo
Dissertação de mestrado
Título da Revista
ISSN da Revista
Título de Volume
Resumo
Nas últimas décadas, o interesse por soluções mais sustentáveis de produção de energia tem aumentado, principalmente, visando soluções para controlar e diminuir os efeitos crescentes do aquecimento global antropogênico. Tal fato só reforçou a necessidade de armazenar energia para uso posterior. Entre os dispositivos de armazenamento de energia mais conhecidos e utilizados atualmente estão as baterias e/ou supercapacitores. Nesse contexto, eletrólitos aquosos superconcentrados (“Water-in-Salt Electrolyte”- WiSE) são uma solução alternativa eficiente, segura e ecologicamente mais correta para substituir eletrólitos de solventes orgânicos em dispositivos de armazenamento de energia. Ao se aumentar a concentração de sal em um eletrólito aquoso, a janela de estabilidade eletroquímica da solução superconcentrada aumenta em relação a eletrólitos aquosos pouco concentrados. Desta forma, os WiSE são considerados bons candidatos a eletrólitos para supercapacitores e podem ser combinados com diferentes tipos de eletrodos, por exemplo, carbetos de metais de transição com estruturas bidimensionais (2D), conhecidos como MXenes, que possuem excelente desempenho em termos de capacitância, quando utiliza dos como eletrodos. Nesta dissertação, apresentamos um estudo computacional detalhado de WiSEs confinados em eletrodos Ti3C2F2 planares e porosos, empregando simulações de dinâmica molecular (DM) com uma extensão do modelo de potencial constante (CPMχ) que considera as diferentes eletronegatividades para eletrodos heterogêneos. No caso dos eletrodos planares, realizamos uma comparação detalhada e quantitativa entre as propriedades calculadas para Ti3C2F2 e eletrodos de grafite usando técnicas de aprendizado não supervisionado para análise de dados. A análise mostrou que independentemente do WiSE e do tipo de eletrodo, os cátions carregam suas esferas de solvatação quando são atraídos pelo eletrodo negativo ou repelidos pelo eletrodo positivo e o comportamento das moléculas de água dentro das camadas mais próximas do eletrodo parece ser mais sensível à natureza química do eletrodo. Nos eletrodos porosos de Ti3C2F2 com fenda de 12,6 Å, o eletrólito NaClO4 proporciona maior acúmulo de carga que os demais WiSEs. Além disso, o mecanismo de carregamento dos eletrodos porosos com WiSEs de sódio muda completamente durante a simulação passando de um mecanismo inicial de adsorção de contra-íons para um mecanismo de dessorção de coíons em tempos mais longos.
In recent decades, interest in more sustainable energy production solutions has increased, mainly aimed at solutions to control and reduce the growing effects of anthropogenic global warming. This fact only reinforced the need to store energy for later use. Among the most well-known and currently used energy storage devices are batteries and/or supercapacitors. In this context, superconcentrated aqueous electrolytes (“Water-in-Salt Electrolyte”- WiSE) are an efficient, safe and more environmentally friendly alternative solution to replace organic solvent electrolytes in energy storage devices. When increasing the salt concentration in an aqueous electrolyte, the electrochemical stability window of the superconcentrated solution increases in relation to less concentrated aqueous electrolytes. Therefore, WiSE are considered good electrolyte candidatesbfor supercapacitors and can be combined with different types of electrodes, for example, transition metal carbides with two-dimensional (2D) structures, known as MXenes. These materials present excellent performance in terms of capacitance when used as electrodes. In this dissertation, we present a detailed computational study of WiSEs confined in planar and porous Ti3C2F2 electrodes, employing molecular dynamics (MD) simulations with an extension of the constant potential method (CPMχ) that considers the different electronegativities for heterogeneous electrodes. In the case of planar electrodes, we performed a detailed and quantitative comparison between the calculated properties for Ti3C2F2 and graphite electrodes using unsupervised learning techniques for data analysis. The analysis for planar electrodes showed that regardless of WiSE and electrode type, cations carry their solvation spheres when they are attracted to the negative electrode or repelled by the positive electrode and the behavior of water molecules within the layers closest to the electrode appears be more sensitive to the chemical nature of the electrode. In the porous Ti3C2F2 electrodes with a pore of 12.6 ˚ A, the NaClO4 electrolyte provides greater charge accumulation than the other WiSEs. Furthermore, the charging mechanism of the porous electrodes with sodium WiSEs changes completely during the simulation, going from an initial counter-ion adsorption mechanism to a co-ion desorption mechanism at longer times.
In recent decades, interest in more sustainable energy production solutions has increased, mainly aimed at solutions to control and reduce the growing effects of anthropogenic global warming. This fact only reinforced the need to store energy for later use. Among the most well-known and currently used energy storage devices are batteries and/or supercapacitors. In this context, superconcentrated aqueous electrolytes (“Water-in-Salt Electrolyte”- WiSE) are an efficient, safe and more environmentally friendly alternative solution to replace organic solvent electrolytes in energy storage devices. When increasing the salt concentration in an aqueous electrolyte, the electrochemical stability window of the superconcentrated solution increases in relation to less concentrated aqueous electrolytes. Therefore, WiSE are considered good electrolyte candidatesbfor supercapacitors and can be combined with different types of electrodes, for example, transition metal carbides with two-dimensional (2D) structures, known as MXenes. These materials present excellent performance in terms of capacitance when used as electrodes. In this dissertation, we present a detailed computational study of WiSEs confined in planar and porous Ti3C2F2 electrodes, employing molecular dynamics (MD) simulations with an extension of the constant potential method (CPMχ) that considers the different electronegativities for heterogeneous electrodes. In the case of planar electrodes, we performed a detailed and quantitative comparison between the calculated properties for Ti3C2F2 and graphite electrodes using unsupervised learning techniques for data analysis. The analysis for planar electrodes showed that regardless of WiSE and electrode type, cations carry their solvation spheres when they are attracted to the negative electrode or repelled by the positive electrode and the behavior of water molecules within the layers closest to the electrode appears be more sensitive to the chemical nature of the electrode. In the porous Ti3C2F2 electrodes with a pore of 12.6 ˚ A, the NaClO4 electrolyte provides greater charge accumulation than the other WiSEs. Furthermore, the charging mechanism of the porous electrodes with sodium WiSEs changes completely during the simulation, going from an initial counter-ion adsorption mechanism to a co-ion desorption mechanism at longer times.