Volume 2, Issue 2, Pages 299-310 (February 2017) A Catalytic Etching-Wetting-Dewetting Mechanism in the Formation of Hollow Graphitic Carbon Fiber  Yuming Chen, Jichen Dong, Lu Qiu, Xiaoyan Li, Qianqian Li, Hongtao Wang, Shijing Liang, Haimin Yao, Haitao Huang, Huajian Gao, Jang-Kyo Kim, Feng Ding, Limin Zhou  Chem  Volume 2, Issue 2, Pages 299-310 (February 2017) DOI: 10.1016/j.chempr.2017.01.005 Copyright © 2017 Elsevier Inc. Terms and Conditions

Chem 2017 2, 299-310DOI: (10.1016/j.chempr.2017.01.005) Copyright © 2017 Elsevier Inc. Terms and Conditions

Figure 1 Schematics and Characterization of the Hollow Graphitic Carbon Nanofiber (A) Schematics of the HGCNF design by an in situ TEM setup. (B and C) TEM and HRTEM images of (B) Ni-carbon composite and (C) HGCNF obtained by application of 2.7 V between Ni-carbon composite nanofiber and Au rod. (D–G) Low- and high-magnification TEM and HRTEM images of HGCNFs with a hollow sphere and tunnel structure. Scale bars, 5 nm (B and C), 500 nm (D), 200 nm (E), 20 nm (F), and 50 nm (G). See also Figures S1 and S2. Chem 2017 2, 299-310DOI: (10.1016/j.chempr.2017.01.005) Copyright © 2017 Elsevier Inc. Terms and Conditions

Figure 2 TEM Images Showing the EEBC Process Accompanied by Evaporation of the Ni Particle The images were acquired in situ with a voltage of 3.5 V and current of 99 μA. Images (A)–(L) show the sequence of the formation of the hollow graphitic sphere and tunnel structure. Scale bars, 100 nm (A–K) and 10 nm (L). See also Figures S3–S5 and Movie S1. Chem 2017 2, 299-310DOI: (10.1016/j.chempr.2017.01.005) Copyright © 2017 Elsevier Inc. Terms and Conditions

Figure 3 Illustration of Three Processes that Form the Pores and Tunnels in the Amorphous Carbon Fiber (A1 and A2) Evaporation of Ni from the surface of the fiber leads to a spherical graphitic pore. (B1–B6) The EEBC process accompanied by evaporation of the Ni forms a graphitic tunnel in the fiber. (C1–C6) The EEC process of forming a tunnel in the fiber. Gray, black, and blue represent the amorphous carbon, graphitic carbon, and Ni, respectively, in all panels. The inset shows the level of graphitization of the tunnel wall, where a transition from amorphous carbon (gray) to highly graphitized carbon (black) can be clearly seen. The driving force from the low-adhesion wall to the high-adhesion tip is also shown by arrows. Chem 2017 2, 299-310DOI: (10.1016/j.chempr.2017.01.005) Copyright © 2017 Elsevier Inc. Terms and Conditions

Figure 4 The Mechanism of Wetting and Dewetting of Ni in Amorphous Carbon and High-Quality Graphitic Carbon (A and B) Adhesion between the Ni(111) surface (A) and amorphous carbon or graphene (B) calculated by the DFT method. (C and D) Snapshots taken during the MD simulation of the wetting of the Ni into a hole in amorphous carbon (C) and the evolution of the wall of the hole in the amorphous carbon during the annealing process (D). (E) The energy and the number of hexagons on the wall of the hole of amorphous carbon during the simulation. (F) Snapshots taken during the MD simulation of a dewetting procedure of Ni catalyst from a high-quality CNT, representing a hole with a high-quality graphitic carbon wall. (G) The energy versus time curve during the dewetting procedure. Chem 2017 2, 299-310DOI: (10.1016/j.chempr.2017.01.005) Copyright © 2017 Elsevier Inc. Terms and Conditions

Figure 5 Hole Diameter as a Function of the Atom Number of Ni Clusters The hole diameter is calculated from the average of the hole sizes at 18.75 and 25 ps during the MD simulation. See also Figures S6–S8. Chem 2017 2, 299-310DOI: (10.1016/j.chempr.2017.01.005) Copyright © 2017 Elsevier Inc. Terms and Conditions

Figure 6 Gas Adsorption Analysis of the Prepared Materials CO2 adsorption isotherms (A) and CO2 TPD profiles of the HGCNFs and CNFs (B). See also Figures S9–S14. Chem 2017 2, 299-310DOI: (10.1016/j.chempr.2017.01.005) Copyright © 2017 Elsevier Inc. Terms and Conditions