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Sitio activo revelado para la oxidación del agua en δ-MnO inducido electroquímicamente: papel de la transición de

Ye-Fei Li¹, Zhi-Pan Liu¹

¹Collaborative Innovation Center of Chemistry for Energy Material, Key Laboratory of Computational Physical Science (Ministry of Education), Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Department of Chemistry, Fudan University , Shanghai 200433, China.

Journal of the American Chemical Society

|January 16, 2018

Resumen

Los investigadores identificaron un nuevo catalizador de óxido de manganeso (MnO) altamente activo para la división artificial del agua. Un sitio de manganeso defectuoso específico, que imita el fotosistema II de la naturaleza, aumenta significativamente la eficiencia de la reacción de evolución del oxígeno (OER).

Área de la Ciencia:

Ciencias de los materiales
La electroquímica
Catálisis

Sus antecedentes:

Los óxidos de manganeso (MnO_x) se estudian ampliamente como catalizadores para la división artificial del agua, con el objetivo de replicar la fotosíntesis natural.
Los catalizadores más activos de MnO_x para la reacción de evolución del oxígeno (OER) a menudo se derivan de estructuras de espinela, formando una capa δ-MnO₂ in situ, pero sus sitios activos siguen siendo poco conocidos.
Comprender los mecanismos a nivel atómico de la transformación de MnO_x e identificar los sitios activos es crucial para diseñar catalizadores eficientes de división de agua.

Objetivo del estudio:

Para aclarar el mecanismo a nivel atómico de la transición de la fase sólida de espinela a la capa Mn₃O₄ en electrolitos acuosos.
Identificar los sitios activos específicos responsables de la alta actividad OER en los catalizadores de MnO_x.
Comprender cómo los defectos estructurales influyen en el rendimiento catalítico para la división del agua.

Principales métodos:

Método estocástico de muestreo por vía de caminata por superficie (SSW) para investigar el mecanismo de transición de fase sólida.
Cálculos basados en principios para evaluar la actividad OER de diferentes estructuras y sitios de defectos de MnO_x.
Análisis de las transformaciones estructurales, incluida la disolución, la dislocación y la modificación de la capa de Mn.

Principales resultados:

La transición de espinela a capa procede a través de una fase transitorio H_0.5MnO₂ formado a altas tensiones.
Esta transición genera diversas estructuras defectuosas de MnO_x, incluidas las con vacantes de Mn.
Un sitio de borde específico con una vacante de Mn vecina, con una estructura de "pseudocubana con una esquina faltante", exhibe una actividad OER superior con un sobrepotencial bajo de 0,59 V.

Conclusiones:

La alta actividad OER de los catalizadores de MnO_x se origina en sitios defectuosos, particularmente aquellos con vacíos de Mn, que mejoran la adsorción intermedia.
La estructura del sitio activo identificado comparte similitudes con los centros catalíticos en el fotosistema II (PSII) de la naturaleza.
Esta investigación proporciona información a nivel atómico sobre el diseño del catalizador MnO para una división artificial eficiente del agua.

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