Theoretical study of the Grotthuss mechanism for hydroxide ions in a homogeneous membrane used in alkaline fuel cells
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Se realizaron simulaciones computacionales para analizar y caracterizar el transporte por difusión estructural a través de la membrana de intercambio aniónico (AEM) funcionalizada de poliestireno-bloque-poli(etileno-ran-butileno)-bloque-poliestireno (QSEBS). Primero, se realizaron simulaciones utilizando la teoría funcionales de densidad (DFT) para generar la estructura de un segmento hidratado de la membrana QSEBS en dos niveles de hidratación. En segundo lugar, se realizaron simulaciones de dinámica molecular ab initio (AIMD) para identificar y describir las características de la difusión estructural con respecto a la hidratación del polímero conductor, y la localización y patrón de solvatación de los iones hidróxido. Luego, se estimaron la difusividad y conductividad del ion hidróxido y se compararon con los datos de simulaciones en agua pura, otras AEM, y la conductividad experimental para QSEBS hidratado. Finalmente, se presenta una imagen detallada de la difusión estructural en una AEM hidratada junto con una guía, basada en hallazgos obtenidos de las simulaciones, que compila las características clave que debe tener una AEM para promover un transporte eficiente por difusión estructural en cualquier nivel de hidratación y, por lo tanto, logre la mayor conductividad de hidróxido posible.
Computational simulations are carried out to analyze and characterize the transport via structural diffusion through the functionalized polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (QSEBS) anion-exchange membrane (AEM). First, simulations using density functional theory (DFT) are performed to generate the structure of a hydrated segment of QSEBS membrane at two hydration levels. Second, ab initio molecular dynamics (AIMD) simulations are performed to identify and describe the characteristics of structural diffusion with respect to hydration of the conductive polymer and location and solvation pattern of hydroxide ions. Then, hydroxide diffusivity and conductivity are estimated and compared with data from simulations in bulk water, other AEM systems and experimental conductivity for hydrated QSEBS. Finally, a detailed picture of structural diffusion in a hydrated AEM is presented along with a guideline based on insights obtained from simulations that compiles the key characteristics that an AEM should have to promote an efficient transport by structural diffusion at any hydration level, and, thus, achieving the highest hydroxide conductivity as possible.
Computational simulations are carried out to analyze and characterize the transport via structural diffusion through the functionalized polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (QSEBS) anion-exchange membrane (AEM). First, simulations using density functional theory (DFT) are performed to generate the structure of a hydrated segment of QSEBS membrane at two hydration levels. Second, ab initio molecular dynamics (AIMD) simulations are performed to identify and describe the characteristics of structural diffusion with respect to hydration of the conductive polymer and location and solvation pattern of hydroxide ions. Then, hydroxide diffusivity and conductivity are estimated and compared with data from simulations in bulk water, other AEM systems and experimental conductivity for hydrated QSEBS. Finally, a detailed picture of structural diffusion in a hydrated AEM is presented along with a guideline based on insights obtained from simulations that compiles the key characteristics that an AEM should have to promote an efficient transport by structural diffusion at any hydration level, and, thus, achieving the highest hydroxide conductivity as possible.
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Fuel Cell; Celda de combustible; Anion-Exchange Membrane; Membrana de intercambio aniónico; Ionic Conductivity; Conductividad iónica; Difusión estructural; Structural Diffusion; Density Functional Theory; Teoría de funcionales de densidad; ab initio Molecular Dynamics; Dinámica molecular ab-initio; ab initio Molecular Dynamics
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Castañeda, S. (2020). Theoretical study of the Grotthuss mechanism for hydroxide ions in a homogeneous membrane used in alkaline fuel cells. Universidad Nacional de Colombia, Medellín, Colombia.