Atomic-Scale In Situ Self-Catalysis Growth of Graphite Shells via Pyrolysis of Various Metal Phthalocyanines

Carbon nanomaterials, as novel functional and structural materials with unique properties, hold significant potential in information technology and nanodevices. However, the self-catalytic growth mechanism of graphite shells derived from carbon sources, facilitated by diverse catalysts, necessitates further exhaustive investigation. To tackle this challenge, we conducted a study utilizing environmental transmission electron microscopy (ETEM) at atomic resolution to investigate the pyrolysis of metal phthalocyanine (MPc) compounds containing various central metals, including Ni, Co, Cu, and Zn. The results reveal that carbon atoms initially dissolve into Ni and Co, leading to the formation of metal carbides that subsequently act as catalysts. Upon achieving carbon saturation, these atoms precipitate outward from the interior, fostering the growth of graphite shells through a bulk growth mode. In contrast, for Cu and Zn, carbon atoms migrate and accumulate on the metal surface, resulting in the growth of graphite shells via a surface growth mode. The distinct growth mechanisms, i.e., bulk growth and surface growth, are intricately governed by the binding energy between carbon atoms and the catalysts, as well as the carbon solubility in the metal. These factors are closely tied to the number and energy of the metals’ d-electrons because more vacant d-orbitals easily forming more coordination numbers. These insights offer profound understanding into the fundamental principles of metal-catalyzed graphite shell growth and provide a strategic roadmap for selecting and designing catalysts that can can optimize the synthesis of desirable carbon nanomaterials.