One-step structure modulation of electrospun metal-loaded carbon nanofibers: Redox reaction controlled calcination

For expanding the functionalities of carbon (C) nanofibers, it remains a challenge to optimize the hybrid structures of metal/C nanofibers such as the secondary nanostructures of C nanofibers and the morphologies of metallic species. Herein, for the first time, we successfully fabricated diversely structured metal/C nanofibers from the same electrospun nanofiber by modulating redox reactions during the calcination. It is based on the selective oxidation, which induces metal reduction and C oxidation. Oxygen partial pressure enables to control the degree of C decomposition. This method is applicable for metals whose oxidation tendency is lower than C. In the pressure range from 1.0 to 6.0×10^-2 Torr, fully filled C nanofibers, Cu/C core/shell nanofibers, hollow C nanofibers, and porous/hollow C nanofibers are formed accordingly. Pressure and time as kinetic factors of calcination affect the nanoscale Kirkendall effect used for hollow C structure formation. As more C decomposes, the inner diameter of the hollow C structure increases. After formation of the hollow C structure, Cu diffuses either inward or outward for stress relaxation and then agglomerates by Ostwald ripening. Our one-step synthesis provides a standard fabrication scheme for optimizing the structures of metal/C nanofibers, which can induce high performances in widespread applications.