BASIC CONCEPTS AND AN OVERVIEW - Foundations of Nanotechnology: Pore Size in Carbon-Based Nano-Adsorbents - page 64

of air. Gasoline vapor is absorbed into activated carbon in a device called “canis-
ter” during parking and reused by passing air through adsorbed activated carbon
during running. For activated carbon in the car canister, a specific pore structure
is required. For the evaluation of the performance of car canister, adsorption/de-
sorption of butane gas has often been used. In the recent work, direct gravimetric
measurement of adsorption of gasoline vapor was carried out, which was not a
standardized method for car canister, and also no experiment on desorption of
gasoline vapor was done. The confirmation of the results is demanded by using
butane gas [1].
1.1.11.4 CARBON ELECTRODE FOR ELECTRIC DOUBLE LAYER
CAPACITORS (EDLC)
As mention before in Section 1.4, because EDLC is on the basis of the formation
of electric double layer at the electrode/electrolyte interface, which is due to the
physical adsorption of electrolyte ions, activated carbons with high surface area
are usually used as electrode materials and their pore size distribution (PSD) is
pointed out. To have an influence in EDLC performance Capacitance of EDLCs
was possible to be explained by dividing into two capacitances of the surface due
to micropores (microporous surface area) and of that due to larger pores (evalu-
ated as external surface area) on different activated carbons. Porous carbons are
characterized by extremely large BET surface areas that range from 500 to 3000
m 2 g −1 . This surface area largely arises from a complex interconnected network
of internal pores. Micropores have a high surface area to volume ratio and, con-
sequently, when present in significant proportions are a major contributor to the
measured area of high surface area activated carbons. Micropore sizes extend
down to molecular dimensions and play an important role in the selectivity of
adsorption-based processes, through restricted diffusion and molecular sieve ef-
fects. Fine micropores also exhibit a greater adsorbent adsorbate affinity due to
the overlap of adsorption forces from opposing pore walls. Accordingly, adsorp-
tion in fine pores can occur via a pore filling mechanism rather than solely by
surface coverage (as is assumed by the Langmuir and BET calculations of sur-
face area). In such cases, the conversion of adsorption data into an estimate of
surface area, by the application of the BET equation, can lead to unrealistically
high surface area estimates. Clearly, the pore size distribution of porous carbons
influences to a large degree the fundamental performance criteria of carbon-based
super-capacitors, the relationship between power and energy density, and the de-
pendence of performance on frequency [20, 34, 45].
Not surprisingly, therefore, considerable research is presently being directed
towards the development of carbon materials with a tailored pore size distribu-
tion to yield high capacitance and low resistance. Electrodes Electric double layer
capacitors (EDLCs) are expected to be one of the promising devices for electric
energy storage and a variety of applications have been developed, for example,for
memory back-up, cold start vehicle assist, storage for solar cell power, and also