owned to remarkable physical and chemical properties. [1] As for both scientific and industrial interests, Ni-catalyzed chemical vapor deposition (CVD) is the widely used for its high yields and low cost. [2] Whereas, fabricating carbon materials with welldefined structure, e.g., specific stacking layers and helical angle, is still challenging due to the insufficient knowledge on dynamics control of carbon growth. [3] On the other hand, in catalysis reactions where nickel is involved, the outstanding ability of CC reforming and hydrogen activation ensures ideal catalytic performance of cracking and hydrogenation, but simultaneously suffering from coking due to uncontrollable carbon formation. [4] Numerous solutions have been applied to restrain the unwanted carbon growth but bring limited efficiency. [5] Therefore, from perspectives of either facilitating catalytic reaction of long-term stability with minimized coking, or fabricating carbon materials of specific layers and stacking architecture, it is of high importance to control the migration and coupling processes of carbon atoms in Ni catalyst based on well understanding about reaction dynamics. [6] Although Ni-catalyzed carbon growth has been studied in previous research, detailed knowledge is still ambiguous, Benefitting from outstanding ability of CC reforming and hydrogen activation, nickel is widely applied for heterogeneous catalysis or producing high-quality carbon structures. This high activity simultaneously induces uncontrollable carbon formation, known as coking. However, the activity origin for growing carbon species remains in debate between the on metallic facets induction and nickel carbide segregation. Herein, carbon growth on Ni catalyst is tracked via in situ microscopy methods. Evidence derived from high-resolution transmission electron microscopy imaging, diffraction, and energy loss spectroscopy unambiguously identifies Ni 3 C as the active phase, as opposed to metallic Ni nickel or surface carbides as traditionally believed. Specifically, Ni 3 C particle grows carbon nanofibers (CNF) layer-by-layer through synchronized oscillation of tip stretch and atomic step fluctuations. There is an anisotropic stress distribution in Ni 3 C that provides the lifting force during nanofiber growth. Density functional theory computations show that it is thermodynamically favorable for Ni 3 C to decompose into Ni and surface-adsorbed carbon. Carbonaceous deposits aggregate asymmetrically round the particle because partial surface is exposed to the hydrocarbon environment whereas the bottom side is shielded by the support. This induces a carbon concentration gradient within the particle, which drives C migration through Ni 3 C phase before it exits as CNF growth.The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/smtd.202200235.
IntroductionControllable synthesis of carbon materials, e.g., nanotubes (CNTs) and graphene, with desired structures attracts much attention
