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Estudios mecánicos de la electrólisis del agua y la electrooxidación del hidrógeno en celdas electroquímicas de óxido
Chunjuan Zhang1, Yi Yu, Michael E Grass
1Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742, USA.
Journal of the American Chemical Society
|July 5, 2013
Resumen
Este estudio utilizó la espectroscopia de fotoelectrones de rayos X de presión ambiente (APXPS) para investigar los electrodos de ceria para la división del agua y la oxidación del hidrógeno. Reveló un paso de limitación de velocidad compartido y una capa de dipolo superficial, crucial para comprender la electrocatálisis.
Área de la Ciencia:
- Ciencia de los materiales Ciencia de los materiales.
- La electroquímica es electroquímica.
- Ciencias de la superficie Ciencias de la superficie.
Sus antecedentes:
- Las células electroquímicas de óxido sólido (SOC) son vitales para la conversión de energía.
- Comprender los mecanismos de los electrodos de ceria (CeO2-x) es clave para una catálisis eficiente.
- Las reacciones electrocatalíticas como la división del agua y la oxidación del hidrógeno requieren conocimientos mecanicistas detallados.
Objetivo del estudio:
- Para dilucidar el mecanismo de la división electrocatalítica del agua y la electro-oxidación del hidrógeno en electrodos de ceria.
- Para investigar el papel de los intermedios superficiales y la separación de cargas en la interfaz gas-sólido.
- Para identificar el paso que limita la velocidad tanto en las reacciones de avance como en las de retroceso.
Principales métodos:
- Espectroscopia de fotoelectrones de rayos X (APXPS) con presión ambiente a ~700 °C.
- Utilizando una célula electroquímica de óxido sólido (SOC) de un solo lado.
- In situ XPS combinado con cálculos de DFT.
Principales resultados:
- Se observó una acumulación transitoria de productos intermedios superficiales (OH ((-) y Ce ((3+)).
- Separación de carga demostrada exclusivamente en la región electroquímica activa.
- Identificó un paso común de transferencia de carga que limita la velocidad tanto para la electrólisis del agua como para la oxidación del hidrógeno.
- Se reveló una diferencia de 0,25 eV en los potenciales superficiales para OH(-) y O(2-) durante la electrólisis del agua.
- Se mostraron cambios significativos en las concentraciones superficiales de OH(-) y O(2-) durante la oxidación del hidrógeno.
Conclusiones:
- El mismo paso de transferencia de carga limita la velocidad tanto para la electrólisis del agua como para la electrooxidación del hidrógeno en ceria.
- Una capa de dipolo de superficie inducida, que actúa como una capa doble electroquímica, se forma en la interfaz gas-sólido.
- La separación potencial proviene de la polarización reducida del enlace Ce-OH debido al aumento de la concentración de superficie de Ce3+.
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