Solvent-induced porosity control of carbon nanofiber webs for supercapacitor

Abstract

A simple and scalable method is reported for fabricating a porosity-controlled carbon nanofibers with a skin-core texture by electrospinning a selected blend of polymer solutions. Simple thermal treatment of the electrospun nanofibers from solution blends of various compositions creates suitable ultramicropores on the surface of carbon nanofibers that can accommodate many ions, removing the need for an activation step. The intrinsic properties of the electrode (e.g., nanometre-size diameter, high specific surface area, narrow pore size distribution, tuneable porosity, shallow pore depth, and good ionic accessibility) enable construction of supercapacitors with large specific capacitance (130.7 Fg -1 ), high power (100 kWkg -1 ), and energy density (15.0 Whkg -1 ).Keywords: Porosity, Skin-core, Electrospinning, Pore size distribution, Supercapacitor 3 1. Introduction Due to their high power density and long life-time, electrochemical capacitors are promising power sources for portable electronic systems and automotive applications [1][2][3]. To improve the performance of these capacitors, several approaches have been investigated (e.g., controlling the pore size distribution, introducing electroactive metallic particles or electron conducting polymers, and fabricating hybrid-type cells) [4][5][6]. Among the many types of active materials, carbon nanofibers (CNFs) are of great practical importance due to their flexibility and high aspect ratio (above 10 6 ). Moreover, to improve the energy density and ion transport within electrode materials, thin films consisting of carbon nanotubes and CNFs have been suggested as promising flexible electrodes for supercapacitors [7][8][9]. In this work, we investigated this approach for improving energy storage efficiency by narrow distribution of pore sizes, which can enhance the ionic accessibility into the pores polyacrylonitrile(PAN)/pitch-based CNFs having a skin-core structure. Further, the size of pores formed in the surface of the fiber can be controlled to an appropriate degree. Experimental FabricationThe pitch provided through condensation of the pyrolized fuel oil (PFO) with Cl 2 by Hanwha Chemical Co. Korea. The PFO used as the raw material is a heavy residual oil as by-product from naphtha cracking. The properties of the pitch used are summarized in Table 1. The concentration of pitch in THF was varied between 50 and 20 wt. %. A solution of PAN in DMF was added to pitch in THF solution achieve a PAN/pitch weight ratio of 7/3 wt.%. To produce a web, a voltage of 20 kV was applied to the positively charged capillary, and a tip-to-collector distance of 25 cm was maintained during the electrospinning process. The nanofibers were stabilized in air and carbonized at 1000 °C in a horizontal furnace under a flow of nitrogen.2.2.Characterization The CNFs were characterized by SEM (Hitachi, S-4700, Japan), TEM (using JEOL JEM-2010 FEF), and nitrogen adsorption-desorption isotherms (ASAP2010, Micromeritics Instruments Co.). The full range of pore sizes over a continuo...

Microwave-Assisted Oxidation of Electrospun Turbostratic Carbon Nanofibers for Tailoring Energy Storage Capabilities

“…130 -246 F/g). [15,[63][64][65][66][67][68][69][70][71][72][73][74][75] Furthermore, at such a high scan rate (i.e., 0.1 V/s), the capacitance value of ECNF-M3 compared favorably to those of many other carbon-based supercapacitor materials, including conventional systems such as mesoporous carbon (ca. 150 F/g) [37][38][39] and activated carbon (<120 F/g), [40][41][42] as well as recently reported carbon nanomaterials such as carbon nanocages (185 F/g), [36] carbon nanococoons (175 F/g), [43] and graphene (ca.…”

“…Moreover, we demonstrate, for the first time, that this microwaveassisted oxidation process can be used to vary the capacitive energy storage capabilities of ECNFs. Previously, control over the capacitive performance of ECNFs was achieved through use of different polymers as carbon precursors, [63][64][65][66][67][68][69][70][71][72] and addition of ZnCl 2 , [15] V 2 O 5 , [73] or silver nanoparticles. [74,75] Interestingly, we find a non-monotonic relationship between the oxidation degree of ECNFs and their electrocapacitive performance.…”

A universal equivalent circuit for carbon-based supercapacitors

“…For this reason, carbon has become the material of choice for many commercial supercapacitors. Among the types of carbon that have been studied in detail are activated carbon (the industry standard) [6][7][8][9][10][11][12][13], various templated carbons [14][15][16][17][18][19][20][21][22][23], carbon black [24][25][26][27], carbon aerogel [28][29][30][31][32], carbon nanotubes [33][34][35][36][37][38][39][40][41][42][43][44][45][46], and graphene [47][48][49][50][51][52][53][54][55]…”

Performance of Activated Carbon from Salvia miltiorrhiza Roots as the Electrode Material for Supercapacitors

“…On the basis of fundamental mechanisms, various carbon materials, such as activated carbons, graphene (Zhang et al 2012), carbon nanotubes (Al-Zubaidi et al 2012), and carbon nanofibers (Kim et al 2011), depend on electrostatic ion adsorption on electrode/electrolyte interface via the formation of electric double layers. Hierarchical porous ACs with high Brunauer-Emmett-Teller (BET) areas, especially within a range of 1000 m 2 /g to 3000 m 2 /g, are the most promising materials to make electrodes for electric double-layer capacitors (EDLCs) in the supercapacitor industry.…”