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Movilidad de electrones y agujeros en hematita a granel a partir de la teoría funcional de densidad con restricción
Christian S Ahart1, Kevin M Rosso2, Jochen Blumberger1
1Department of Physics and Astronomy, University College London, London WC1E 6BT, U.K.
Journal of the American Chemical Society
|March 3, 2022
Resumen
Los agujeros en la hematita (α-Fe2O3) forman polarones localizados que causan un transporte lento, mientras que los electrones se deslocalizan en dos sitios, lo que permite una transferencia de carga más rápida para una mejor división fotoelectroquímica del agua.
Área de la Ciencia:
- Ciencias de los materiales
- Química Física
- Química computacional
Sus antecedentes:
- Los óxidos de metales de transición son cruciales para la división fotoelectroquímica del agua.
- Comprender el transporte del portador de carga en estos materiales es clave para mejorar la eficiencia.
- La hematita (α-Fe2O3) es un material ampliamente estudiado para la división del agua, pero sus mecanismos de transporte de carga no se comprenden completamente.
Objetivo del estudio:
- Investigar la naturaleza y los mecanismos de transporte de los agujeros y el exceso de electrones en la hematita.
- Para aclarar los orígenes a nivel atómico del transporte lento del portador de carga.
- Proporcionar conocimientos fundamentales para mejorar la actividad fotocatalítica.
Principales métodos:
- Cálculos periódicos de la teoría funcional de la densidad híbrida con restricción de espín y optimización de la brecha.
- Análisis de la localización del portador de carga y de la distorsión de la estructura atómica del material.
- Cálculo de las energías de activación y las movilidades para el transporte de cargas.
Principales resultados:
- Los agujeros en la hematita se localizan como polarones en átomos de hierro individuales debido a la distorsión tetragonal de los enlaces Fe-O circundantes.
- Esta localización polaron conduce a un transporte de salto lento con una movilidad de agujero de 0.031 cm2 / V s.
- Los electrones en exceso se deslocalizan sobre dos unidades de Fe vecinas, lo que resulta en una mayor movilidad de electrones de 0.098 cm2 / V s, aproximadamente tres veces mayor que la de los agujeros.
Conclusiones:
- Los distintos comportamientos de localización de los agujeros y los electrones impactan significativamente sus propiedades de transporte en la hematita.
- La deslocalización de electrones y los desplazamientos espaciales más grandes asociados mejoran la eficiencia del transporte de carga.
- Estos hallazgos ofrecen ideas cruciales para optimizar la hematita para una división fotoelectroquímica eficiente del agua.
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