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Reducción electroquímica del oxígeno disuelto en películas alcalinas de electrolitos de polímeros sólidos

David Novitski¹, Aslan Kosakian², Thomas Weissbach¹

¹Department of Chemistry, Simon Fraser University , Burnaby, British Columbia V5A 1S6, Canada.

Journal of the American Chemical Society

|November 3, 2016

Resumen

El transporte de oxígeno en las células de combustible de membrana de intercambio aniónico es crucial pero poco estudiado. La reducción del contenido de agua del ionómero reduce significativamente la difusión de oxígeno, lo que afecta el rendimiento de la pila de combustible.

Área de la Ciencia:

La electroquímica
Ciencias de los materiales
Ingeniería Química

Sus antecedentes:

El transporte de oxígeno a través de ionómeros es crítico para las células de combustible de membrana de intercambio aniónico (AEMFC).
El agua es un reactivo en la reacción de reducción de oxígeno (ORR) en medios alcalinos, lo que requiere un suministro de agua adecuado.
Las limitaciones del transporte de masa en la capa del catalizador de cátodo son un desafío clave para el rendimiento de AEMFC.

Objetivo del estudio:

Investigar el comportamiento del transporte de masas de la reacción de reducción de oxígeno (ORR) en los iónmeros AEMFC.
Determinar la influencia del contenido de agua de los ionómeros en la difusión y concentración de oxígeno.
Evaluar la exactitud de la ecuación de Shoup-Szabo para la extracción de parámetros de transporte de masas en películas delgadas de ionómero.

Principales métodos:

Cronometría de paso del potencial electroquímico utilizando un electrodo de microdisco Pt.
Prueba de las membranas metiladas de hexametil-p-terfenil polimetilbenzimidazol (HMT-PMBI) y las membranas FAA-3 de Fumatec.
Control de la humedad relativa del 70% al 98% a 60 °C.
Ajuste de la curva no lineal de los transientes de corriente con la ecuación de Shoup-Szabo.
Modelado numérico para evaluar las limitaciones de la ecuación de Shoup-Szabo.

Principales resultados:

Los coeficientes de difusión de oxígeno (D_bO2) disminuyen en dos órdenes de magnitud con la disminución de la humedad relativa (contenido de agua).
Se descubrió que la permeabilidad del oxígeno (D_bO2 · c_bO2) depende fuertemente del contenido de agua del ionómero.
El modelado numérico reveló discrepancias de hasta el 29% para membranas altamente hidratadas utilizando la ecuación de Shoup-Szabo.

Conclusiones:

El contenido de agua en iónos tiene un impacto significativo en el transporte de masa de oxígeno en los AEMFC.
El contenido reducido de agua conduce a disminuciones sustanciales en la difusión de oxígeno, limitando potencialmente el ORR.
La ecuación de Shoup-Szabo puede sobreestimar los parámetros de transporte de masa para las membranas altamente hidratadas debido a los efectos de la interfaz.

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