Estudo computacional de líquidos iônicos confinados como eletrólitos para supercapacitores e como absorvedores de CO2
Data
2023-07-07
Autores
Pereira, Rafael Guimarães 
Orientadores
Siqueira, Leonardo José Amaral de
Tipo
Tese de doutorado
Título da Revista
ISSN da Revista
Título de Volume
Resumo
Por sua versatilidade, sistemas contendo líquidos iônicos confinados entre eletrodos de grafeno
e com voltagem aplicada são estudados na captura de CO2 e como supercapacitores. Embora
a absorção de CO2 por aminas seja altamente eficiente, há grande consumo de energia e a
captura/armazenamento por membranas surge como um método de menor custo, mas sofrem de
baixa permeabilidade a gases. Estímulos externos, como aumento de temperatura e aplicação
de voltagem, são alternativas para melhorar o desempenho. Realizamos simulações de dinâmica
molecular do butil-trimetil-amônio bis(trifluoro-metano-sulfonil)imida ([N1114]+[NTf2]– ), confinado
em carbonos porosos sob aplicação de tensão, como material de membrana para captura de
CO2. O desequilíbrio de íons dentro dos poros imposto pela tensão, por exemplo, o maior
número de [NTf2]– no eletrodo positivo, aumenta não apenas o número de CO2 dentro dos poros,
mas também a taxa de absorção de CO2 no bulk devido a interações favoráveis de CO2 com
[NTf2]– ânions. Aumentando o tamanho dos poros (de 1,2 para 1,5 nm), as mobilidades dos íons
aumentam, o que resulta em uma absorção de gás mais rápida. A melhoria da solubilidade do
gás dentro dos poros e a absorção mais rápida sob tensão aplicada é resultado da mobilidade
dos íons dentro dos poros, do volume livre disponível e da interação gás-ânion favorável dentro
dos poros carregados positivamente. A demanda crescente de energia pressiona por meios mais
eficientes de armazenagem. Os supercapacitores prometem juntar a alta ciclabilidade e potência
dos capacitores e a densidade de energia das baterias. Neste trabalho fizemos simulações de
dinâmica molecular com misturas do líquido iônico [EMIM][NTf2](1 – x)[TMA][NTf2](x) contendo dois
cátions, confinado entre eletrodos porosos de grafeno com porosidade mista. Os resultados
mostraram que o poro mais estreito de 0,75 nm tem papel fundamental no mecanismo de
carregamento, forçando a blindagem iônica e alterando a estrutura na interface do eletrodo.
Mesmo em uma condição onde a viscosidade é maior e a condutividade menor como nas frações
molares de XTMA = 0,25 e 0,50, devido à estrutura, a potência e a densidade de energia são
ótimas, o que pode ser visto no gráfico de Ragone. Os resultados também foram analisados
pela densidade nas direções de simulação Y e Z, pelas curvas de carregamento, e também pelo
mecanismo de carregamento através do parâmetro X.
Due to their versatility, systems containing ionic liquids confined between graphene electrodes and with applied voltage are studied in the capture of CO2 and as supercapacitors. Although the absorption of CO2 by amines is highly efficient, it consumes a lot of energy and the capture/storage by membranes emerges as a lower cost method, but suffers from low permeability to gases. External stimuli, such as temperature increase and voltage application, are alternatives to improve performance. We performed molecular dynamics simulations of butyl-trimethyl-ammonium bis(trifluoro-methanesulfonyl)imide ([N1114]+[NTf2]– ), confined in porous carbons under voltage application, as membrane material for capture of CO2. The imbalance of ions inside the pores imposed by the voltage, for example, the greater number of [NTf2]– on the positive electrode, increases not only the number of CO2 inside the pores, but also the rate of absorption of CO2 in the bulk due to favorable interactions of CO2 with [NTf2]– anions. By increasing the pore size (from 1.2 to 1.5 nm), the ions mobility increase, which results in faster gas absorption. Improved gas solubility within pores and faster absorption under applied voltage is a result of ion mobility within pores, available free volume, and favorable gas-anion interaction within positively charged pores. The growing demand for energy puts pressure on more efficient means of storage. Supercapacitors promise to bring together the high cyclability and power of capacitors and the energy density of batteries. In this work we performed molecular dynamics simulations with ionic liquid mixtures [EMIM][NTf2](1 – x)[TMA][NTf2](x) containing two cations, confined between porous electrodes of graphene with mixed porosity. The results showed that the narrowest pore of 0.75 nm plays a key role in the charging mechanism, forcing ion screening and changing the structure at the electrode interface. Even in a condition where the viscosity is higher and the conductivity lower as in the mole fractions of xTMA = 0.25 and 0.50, due to the structure, the power and the energy density are optimal, which can be seen in Ragone’s graph. The results were also analyzed by density in the Y and Z simulation directions, by the charging curves, and also by the charging mechanism through the X parameter.
Due to their versatility, systems containing ionic liquids confined between graphene electrodes and with applied voltage are studied in the capture of CO2 and as supercapacitors. Although the absorption of CO2 by amines is highly efficient, it consumes a lot of energy and the capture/storage by membranes emerges as a lower cost method, but suffers from low permeability to gases. External stimuli, such as temperature increase and voltage application, are alternatives to improve performance. We performed molecular dynamics simulations of butyl-trimethyl-ammonium bis(trifluoro-methanesulfonyl)imide ([N1114]+[NTf2]– ), confined in porous carbons under voltage application, as membrane material for capture of CO2. The imbalance of ions inside the pores imposed by the voltage, for example, the greater number of [NTf2]– on the positive electrode, increases not only the number of CO2 inside the pores, but also the rate of absorption of CO2 in the bulk due to favorable interactions of CO2 with [NTf2]– anions. By increasing the pore size (from 1.2 to 1.5 nm), the ions mobility increase, which results in faster gas absorption. Improved gas solubility within pores and faster absorption under applied voltage is a result of ion mobility within pores, available free volume, and favorable gas-anion interaction within positively charged pores. The growing demand for energy puts pressure on more efficient means of storage. Supercapacitors promise to bring together the high cyclability and power of capacitors and the energy density of batteries. In this work we performed molecular dynamics simulations with ionic liquid mixtures [EMIM][NTf2](1 – x)[TMA][NTf2](x) containing two cations, confined between porous electrodes of graphene with mixed porosity. The results showed that the narrowest pore of 0.75 nm plays a key role in the charging mechanism, forcing ion screening and changing the structure at the electrode interface. Even in a condition where the viscosity is higher and the conductivity lower as in the mole fractions of xTMA = 0.25 and 0.50, due to the structure, the power and the energy density are optimal, which can be seen in Ragone’s graph. The results were also analyzed by density in the Y and Z simulation directions, by the charging curves, and also by the charging mechanism through the X parameter.