Preparation and Characterization of porous Carbon/Nickel Nanofibers for Supercapacitor

Two polymer solutions of polyacrylonitrile, polyvinyl pyrrolidone, and Ni(CH3COOH)2 in dimethylformamide were electrospun into ternary composite nanofibers, followed by stabilization and carbonization processes to obtain porous carbon/nickel composite nanofibers with diameters of 100-200 nm. The study revealed that carbon/nickel composite nanofibers were successfully prepared, which allowed nickel particles with diameters of 20-70 nm to be uniformly distributed in the carbon nanofibers. It was also observed that the fibrous structures with particles embedded formed and the fibers broke into shorter fibers after sintering. X-ray diffraction indicated that embedded particles crystallized with the face centered cubic structure. The Brunauer-Emmett-Teller analysis revealed that carbon/nickel composite nanofibers with meso-pores possessed larger specific surface area than that of carbon nanofibers. The specific capacitance of the composite nanofiber electrode was as high as 103.8 F/g and showed stable cyclicity (73.8%). INTRODUCTION Over the past few decades, the development of carbon materials of various forms with unique structures and properties has attracted considerable attention because of their potential applications in supercapacitors [1-4]. Traditional activated porous carbon fibers are obtained mainly by chemical activation with KOH [5, 6] or NaOH [7] and physical activation with stream [8, 9] and carbon dioxide [10]. A simple, yet effective and economical technique for creating porous carbon with both large surface area and incorporated functional component is needed. One-dimensional porous carbon fibers [11, 12], and carbon/metal composite fibers [13, 14], with well-controlled pore structures and well-dispersed nanometer scale metallic compounds, are desired for many practical applications. However, only a few studies have covered the carbon/nickel (C/Ni) composites prepared by the method of using electrospinning electrode materials for supercapacitors [15]. Here, we report an easy method to obtain porous carbon/nickel nanofibers with uniform and controllable pore sizes by electrospinning and subsequent carbonization processes, in which two polymer solutions polyacrylonitrile and polyvinyl pyrrolidone (PAN and PVP) and Ni(CH3COOH)2 (Ni(OAc)2) were used as C/Ni composite nanofiber precursors because the PVP phase decomposed during thermal treatment. The porous carbon nanofibers were obtained afterwards. The nickel particles were uniformly incorporated into the porous carbon fibers, which would enhance not only the conductivity of the fiber mat but also the electron transfer between nickel particles and the carbon substrate. The electrochemical behavior and cycling performance of the C/Ni composite nanofibers were also discussed. EXPERIMENTAL Fibers preparation Electrospinning is now a versatile and effective method for fabricating functional nanofibers, which are exceptionally long and uniform in diameter ranging from tens of nanometers to several micrometers [16]. The preparation of the composite nanofibers was reported in our previous work [17]. In