Structure, Morphology and Thermal Stability of Porous Carbon Nanofibers Loaded with Cobalt Nanoparticles

Porous carbon/cobalt (C/Co) composite nanofibers with diameters of 200-300 nm were prepared by electrospinning and subsequent carbonization processes. Two polymer solutions of polyacrylonitrile (PAN), polyvinyl pyrrolidone (PVP), and Co (CH3COOH) 2 (Co (OAc) 2) were used as C/Co composite nanofiber precursors. The study revealed that C/Co composite nanofibers were successfully prepared and cobalt particles with diameters of 20-30 nm were uniformly scattered in the carbon nanofibers. It was also observed that clear fibrous morphology with grainlike particles and good structural integrity were still maintained after calcination. The TGA analysis indicated the improved thermal stability properties of the composite nanofibers. The Brunauer-Emmett-Teller (BET) analysis indicated that C/Co composites nanofibers with meso-pores possessed larger specific surface area than that of carbon nanofibers. INTRODUCTION Porous carbon materials loaded with metal or metal oxide have attracted a great deal of attention because of their versatile applications in catalysis, sensors, electronic devices, gas and liquid separation, and memory storage. Because the composite nanofibers exhibit excellent electrochemical properties with high reversible capacity, especially the porous composite nanofibers, much research effort has been attempted to prepare the composite nanofibers with the method of electrospinning and calcination using a wide variety of polymers and inorganic materials because of its relatively simple preparation and lower cost 7,8 such as C/Ni, C/Cu, C/Co, C/Co3O4, C/Fe3O4. In this study, we prepared grainlike porous C/Co composite nanofibers by electrospinning and subsequent carbonization processes, where two polymer solutions (PAN and PVP) and Co (OAc)2 were used as C/Co composite nanofiber precursors because the PVP phase decomposed during thermal treatment, then the porous carbon nanofibers were obtained. The grainlike cobalt particles were uniformly distributed on the fiber surface and well-dispersed in porous carbon composite nanofibers. EXPERIMENTAL Fibers Preparation In the typical synthesis, the N,N-dimethylformamide (DMF) solutions of PAN/PVP (7:3, 10wt %) containing 50wt% Co(OAc)2 were prepared at room temperature. The molecular weights of PAN and PVP were 79,100 and 40,000, respectively. Homogeneous electrospinning solutions were loaded in a 20 mL syringe with a 0.6 mm inner diameter of the metal needle. The positive voltage, working distance, and flow rate were 15 kV, 15 cm, and 0.4 mL/h, respectively. Nanofibers were collected as a fibrous web on the surface of the aluminum foil. The electrospun PAN/PVP/Co(OAc)2 nanofibers were firstly stabilized in an air environment at 250 C for 4 h (heating rate was 2 C min) and then carbonized at 800 C for 6 h in argon atmosphere (heating rate was 5 C min). For comparison, pure PAN nanofibers were also prepared under the same conditions.