Structural Changes of 2D FexMn1−xO2 Nanosheets for Low‐Temperature Growth of Carbon Nanotubes

The synthesis of carbon nanotubes (CNTs) is usually done by metallic catalysts with a gaseous carbon precursor at high temperature. Yet, mild synthesis conditions can broaden the application of CNTs and their composites. In the present work, it is unraveled why partially substituted Fe ions in 2D MnO2 nanosheets lead to the growth of CNTs at low temperatures of 400−500 °C. The local formation of Fe3C by carbon precursor explains the unusually high catalytic activity of 2D FexMn1−xO2 nanosheets for preparing CNTs. Finally, Fe3C is oxidized to Fe3C/FeOx yolk/shell morphology in ambient atmosphere after the CNT formation reaction. These results shed light on the development of novel catalyst materials that allow for efficiently prepare CNTs under mild conditions for their wider use in energy‐harvesting applications. Preparation of carbon nanotubes (CNTs) in mild conditions is critical for broadening their applications. The unusually high catalytic activity of 2D FexMn1−xO2 nanosheets for the growth of CNTs at low temperature is unraveled using various scanning transmission electron microscopy techniques. Formation of Fe3C during the growth of CNTs and its unique oxidation in ambient condition are investigated.