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The low density of porous carbon nanomaterials for supercapacitor electrodes has limited their widespread application, despite their ultra-high gravimetric capacitance. In this work, we successfully prepared highly densified composite electrodes of graphene and single-walled carbon nanohorns (SWCNHs) using a simple spray-drying method that is suitable for mass production. To prepare the high-density composite electrodes, water-based mixtures of oxidized SWCNHs (NHOs) and graphene oxides (GOs) were spray-dried in heated air; after spray-drying, GOs dispersed in water were agglomerated in spherical clusters containing NHO nanoparticles. The reduced spray-dried GO/NHO (rS-GO/NHO) composite electrodes exhibited an extremely high bulk density of 1.23 g·cm−3, which is almost double that of commercial activated carbon (AC) and reduced NHO (r-NHO) electrodes, and three times higher than that of rS-GO electrodes. Of the materials tested, the rS-GO/NHO composite electrode had the highest volumetric capacitance (80 F·cm−3 at 1 mA·cm−2) and a low sheet resistance (0.005 Ω· sq.−1), which are far superior to those of commercial AC (57 F·cm−3 at 1 mA·cm−2 and 0.293 Ω·sq.−1, respectively), without the need for a conductive material, such as carbon black. We expect that these high-density graphene/SWCNH composite electrodes with high volumetric capacitances can be substituted for commercial AC materials in energy storage devices, such as supercapacitors.

Porous carbon nanofibers (PCNFs) were prepared from electrospinning both without and with a pore generating inorganic material. Next, they were activated with different activation media (N2, H2O, or CO2). The pore size was tailored from 0.64 to 0.81 nm under various activation conditions, and the specific surface area ranged from 404 to 1624 m2·g−1. To determine the charging mechanism of the supercapacitor in an aqueous electrolyte, the normalized capacitance was calculated, and it was compared with the adsorption behavior of the solvent, H2O, separately. The normalized capacitance showed a trend similar to that of H2O adsorption at a low relative pressure (P/P0 = 0.1), which was expected to be driven by the filler–pore wall interaction, indicating that the ions were strongly solvated by the solvent, H2O. The highest normalized capacitance value (32 μF·cm−2 at 1 mA·cm−2) was achieved from PCNFs having a pore size of 0.64 nm, similar to the electrolyte solvated ion sizes. It was observed that both the capacitance and H2O adsorption were achieved near the pore size of 0.64 nm and at a high functionality. It was understood that the adsorption of the solvated ions was primarily driven by the interaction of the solvent, H2O, with the surface functional groups.

The SiC/SiO 2 deposition was performed to improve the oxidation resistive properties of carbon nanofiber (CNF) from electrospinning at elevated temperatures through sol–gel process. The stabilized polyacrylonitrile (PAN) fibers were coated with SiO 2 followed by heat treatment up to 1000 and 1400 °C in an inert argon atmosphere. The chemical compositions of the CNFs surface heat-treated were characterized as C, Si and O existing as SiC and SiO 2 compounds on the surface. The uniform and continuous coating improved the oxidation resistance of the carbon nanofibers. The residual weight of the composite was 70–80% and mixture of SiC, SiO 2 and some residual carbon after exposure to air at 1000 °C.

In this paper, carbon fibers with improved thermal stability and oxidation resistive properties were prepared and evaluated their physical performances under oxidation condition. Carbon fibers were coated with SiC particles dispersed in a polyacrylonitrile solution and then followed by pyrolyzed at 1400 °C to obtain the SiC nanoparticle deposition on the surface of the carbon fiber. The SiC coated carbon fiber showed extended oxidation resistive property as remaining 80–88% of the original weight even at high temperature 1000 °C under air, as compared with the control of zero weight at 600 °C. The effects of the coating conditions on the oxidation resistive properties of the coated fibers were studied in detail.