Denisa Hulicova

Electric double layer capacitance of highly pure single-walled carbon nanotubes (HiPco Buckytubes) in propylene carbonate electrolytes

The double layer capacitance of highly pure single-walled carbon nanotubes (SWCNTs) prepared by the HiPco™ process was measured in 1.0moldm−3LiClO4/propylene carbonate solution. The unpurified SWCNT electrode was mainly composed of a bundle structure of SWCNTs with around 1.0 nm tube diameter, small amount of amorphous carbons, and Fe catalyst particles. The Fe catalysts in the surface of the SWCNT were removed by immersion in HClaq. The αs-SPE analysis of the N2 adsorption isotherms revealed that both the SWCNTs before and after the immersion in HClaq had relatively high specific surface areas of ∼500m2g−1 without microporosity although the tube ends were closed. The SWCNTs showed a gravimetric capacitance of around 45Fg−1. Thus, the specific capacitance per unit surface area was estimated to be around 10μFcm−2, which was higher than that of conventional activated carbon fibers. Furthermore, the capacitance of the SWCNTs did not decrease even at high current density. This good rate property of the SWCNTs is related to the large area of the external surface (∼400m2g−1) on which ion adsorption/desorption can proceed fast because of no ion sieving. On the other hand, most of the Fe catalyst in the SWCNT could be removed by thermal oxidation followed by immersion in HClaq. However, the gravimetric capacitance of this purified SWCNT was not as great as that expected by the correlation of 10μFcm−2. This is related to the formation of amorphous carbons caused by the thermal oxidation.

The polymer blend technique as a method for designing fine carbon materials

The polymer blend technique is proposed as a method for designing fine carbon materials. In principle a blend consisting of polymers with and without carbon residue after heating is subjected to melt-spinning, stabilization and finally carbonization. A combination of two polymers and control of the blend texture are important for using the technique successfully. In this paper, three prepared fine carbon materials are introduced, i.e. carbon fibers including thin and long pores aligned parallel to the fiber, thin carbon fibers 200–300 nm in diameter and carbon nanotubes with 10–20-nm outer diameter. In particular the carbon nanotubes are described in detail to emphasize the great potential of the polymer blend technique. Further possibilities of the technique are also discussed briefly.

Carbon nanotubes prepared by spinning and carbonizing fine core-shell polymer microspheres

Carbon nanotubes prepared from core-shell polymer particles are reported. As depicted in the Figure, polymethylmethacrylate (PMMA) core/polyacrylonitrile (PAN) shell microspheres are blended with a PMMA matrix, spun, and elongated. Then the shell is stabilized and finally carbonized to produce contaminant-free carbon nanotubes.

Electric double layer capacitance of highly pure single-walled carbon nanotubes (HiPco (TM) Buckytubes (TM)) in propylene carbonate electrolytes

The double layer capacitance of highly pure single-walled carbon nanotubes (SWCNTs) prepared by the HiPco™ process was measured in 1.0moldm−3LiClO4/propylene carbonate solution. The unpurified SWCNT electrode was mainly composed of a bundle structure of SWCNTs with around 1.0 nm tube diameter, small amount of amorphous carbons, and Fe catalyst particles. The Fe catalysts in the surface of the SWCNT were removed by immersion in HClaq. The αs-SPE analysis of the N2 adsorption isotherms revealed that both the SWCNTs before and after the immersion in HClaq had relatively high specific surface areas of ∼500m2g−1 without microporosity although the tube ends were closed. The SWCNTs showed a gravimetric capacitance of around 45Fg−1. Thus, the specific capacitance per unit surface area was estimated to be around 10μFcm−2, which was higher than that of conventional activated carbon fibers. Furthermore, the capacitance of the SWCNTs did not decrease even at high current density. This good rate property of the SWCNTs is related to the large area of the external surface (∼400m2g−1) on which ion adsorption/desorption can proceed fast because of no ion sieving. On the other hand, most of the Fe catalyst in the SWCNT could be removed by thermal oxidation followed by immersion in HClaq. However, the gravimetric capacitance of this purified SWCNT was not as great as that expected by the correlation of 10μFcm−2. This is related to the formation of amorphous carbons caused by the thermal oxidation.

Carbon nanotubes prepared from polymer microspheres by spinning and carbonizing

Multi-wall carbon nanotubes (CNTs) with diameters between 10 nm and 20 nm were prepared by melt spinning, stabilizing and carbonizing of fine core/shell-1/shell-2 polymer microspheres. Microspheres were synthesized by three-steps soap free emulsion polymerization of methylmetacrylate (MMA) and acrylonitrile (AN) using potassium persulfate (KPS) as a polymerization radical initiator. The final composition of microspheres was PMMA core/PAN shell-1/PMMA shell-2 and diameter ca. 500 nm. The outer PMMA layer played the role of a matrix polymer. Microspheres were directly melt spun at ca. 300°C followed by stabilization of PAN at 220°C in oxygen and carbonization at 1000°C in nitrogen. TG-DTA study was used for clarifying the PAN thermal behavior during CNTs synthesis. SEM, TEM and HRTEM were used in characterizing the microspheres and CNTs morphology.

Electric double layer capacitance of highly pure single-walled carbon nanotubes () in propylene carbonate electrolytes

The double layer capacitance of highly pure single-walled carbon nanotubes (SWCNTs) prepared by the HiPco™ process was measured in 1.0moldm−3LiClO4/propylene carbonate solution. The unpurified SWCNT electrode was mainly composed of a bundle structure of SWCNTs with around 1.0 nm tube diameter, small amount of amorphous carbons, and Fe catalyst particles. The Fe catalysts in the surface of the SWCNT were removed by immersion in HClaq. The αs-SPE analysis of the N2 adsorption isotherms revealed that both the SWCNTs before and after the immersion in HClaq had relatively high specific surface areas of ∼500m2g−1 without microporosity although the tube ends were closed. The SWCNTs showed a gravimetric capacitance of around 45Fg−1. Thus, the specific capacitance per unit surface area was estimated to be around 10μFcm−2, which was higher than that of conventional activated carbon fibers. Furthermore, the capacitance of the SWCNTs did not decrease even at high current density. This good rate property of the SWCNTs is related to the large area of the external surface (∼400m2g−1) on which ion adsorption/desorption can proceed fast because of no ion sieving. On the other hand, most of the Fe catalyst in the SWCNT could be removed by thermal oxidation followed by immersion in HClaq. However, the gravimetric capacitance of this purified SWCNT was not as great as that expected by the correlation of 10μFcm−2. This is related to the formation of amorphous carbons caused by the thermal oxidation.