BASIC CONCEPTS AND AN OVERVIEW - Foundations of Nanotechnology: Pore Size in Carbon-Based Nano-Adsorbents - page 9

carbon nanofibers are expected to be more useful than spherical activated carbon
in allowing the relationship between pore structure and electrochemical properties
to be investigated to prepare the polarizable electrodes for experimental EDLCs,
EDLCs are well documented to exhibit significantly higher specific powers and
longer cycle lifetimes compared with those of most of rechargeable batteries, in-
cluding lead acid, Ni-MH, and Li-ion batteries [20, 34, 45].
Hence, EDLCs have attracted considerable interest, given the ever-increasing
demands of electric vehicles, portable electronic devices, and power sources for
memory backup. The capacitance of an EDLC depends on the surface area of
the electrode materials. Therefore, activated carbons are necessary materials for
EDLC electrodes because of their large surface area, highly porous structure,
good adsorption properties, and high electrical conductivity. The electrochemical
performance of EDLCs is related to the surface area, the pore structure, and the
surface chemistry of the porous carbon. Various types of porous carbon have been
widely studied for use as electrode materials for EDLCs. Their unusual structural
and electronic properties make the carbon nanostructures applicable in the elec-
trode materials of EDLCs and batteries. The principle of electrochemical capaci-
tors, physical adsorption/desorption of electrolyte ions in solution, was applied
for water purification by using different carbon materials [108, 113].
This work is concerned with such pore control methods proposed by research-
ers that their ultimate goal is to establish a method with tailoring carbon material
pore structures to reach any kind of application. Researchers would much like to
effort that have made to control micro and mesopores in carbon materials, and
prepare them in achieving the final goal. The presence of mesopores in electrodes
based on CNTs, due to the central canal and entanglement enables easy access of
ions from electrolyte. For electrodes built from multi walled carbon nanotubes
(MWCNTs), specific capacitance in a range of 4-135 F/g was found. For single
walled carbon nanotubes (SWCNTs) a maximum specific capacitance of 180 F/g
is reported. Acomparative investigation of the specific capacitance achieved with
CNTs and activated carbon material reveals the fact activated carbon material ex-
hibited significantly higher capacitance. Super capacitor CNTs-based electrodes
were fabricated by direct synthesis of nanotubes on the bulk Ni substrates, by
means of plasma enhanced chemical vapor deposition of methane and hydro-
gen. The specific capacitance of electrodes with such nanotubes was of 49 F/g.
MWCNTs were electrochemically oxidized and their performance in EDLCs was
studied [45, 64, 68].
1.1.5 CARBON NANOTUBE (CNT): PROPERTIES AND APPLICATION
An article by Iijima that showed that carbon nanotubes are formed during arc-
discharge synthesis of C 60 , and other fullerenes also triggered an outburst of the
interest in carbon nanofibers and nanotubes. These nanotubes may be even single
walled, whereas low-temperature, catalytically grown tubes are multi-walled.