Hierarchical Nanostructures: Application to Supercapacitors - Hierarchical Nanostructures for Energy Devices - page 214

d n 3 r 4 n g | 4

Figure 9.6 Specific capacitance of various electrode materials for supercapacitors.

Reproduced from ref. 25 by permission of The Electrochemical Society.

on the choice of the electrolyte and the experimental conditions including
scan rate, current load, and amount of material loading. 10 Ranges of values
are provided in this section, and readers are encouraged to refer to the
individual studies for more details.

.

9.3.1 Activated Carbon
Activated carbon has been a conventional material for carbon-based EDLCs.
It can be produced from carbon-rich organic precursors via high-tempera-
ture carbonization in an inert atmosphere. A post-oxidation process in the
presence of CO 2 , water, and KOH can further enhance the surface properties.
Activated carbon can be derived from abundant natural resources (wood,
lignin, coconut shell, etc.) or other types of carbon such as coal and pet-
roleum coke. In addition to the cheap carbon resources, the large-scale
manufacturing process has enabled activated carbon to be commercially
available.
Activated carbon consists of a myriad of micropores ( o 2 nm) and the SSA
can reach 1000-2000 m 2 g 1 . 26 However, a lack of mesoporous ion channels
in activated carbon limits the accessibility of electrolyte ions and thereby its
capacitance is restricted to only a few tens of F g 1 . Moreover, activated
carbon has a poor electrical conductivity, due to the low graphitic quality
and the low connectivity between activated carbon agglomerates. The ESR of
the activated carbon electrode is therefore higher than those of other
graphitic carbon materials that will be discussed in the next section.