ROLE OF ACTIVATED CARBON IN

SUPERCAPACITOR

1By - Kinjal

WHAT IS A SUPERCAPACITOR?

It can be defined as a energy storage device that stores energy

electrostatically by polarizing an electrolytic solution.

Electrochemical Double Layer Capacitors (EDLCs) – also called

supercapacitors (SC) - are electrochemical capacitors that have

high capacitance and high energy density when compared to

common capacitors, and higher power density when compared to

batteries.

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Energy is stored in ultracapacitor by polarizing the electrolytic

solution. The charges are separated via electrode –electrolyte

interface.

PRINCIPLE

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Electrolyte

+ -

Electrode

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CONSTRUCTION

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CONSTRUCTION

Most EDLC's are constructed from:

two carbon based electrodes (mostly activated carbon with a

very high surface area),

an electrolyte (aqueous or organic) and

a separator (that allows the transfer of ions, but provides

electronic insulation between the electrodes).

As voltage is applied, ions in the electrolyte solution diffuse across

the separator into the pores of the electrode of opposite charge.

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WORKING

When the voltage is applied to positive plate, it attractsnegative ions from electrolyte.

When the voltage is applied to negative plate, it attractspositive ions from electrolyte.

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WORKING

Charge accumulates at the interface between the electrodes and

the electrolyte (the double layer phenomenon that occurs

between a conductive solid and a liquid solution interface),

and forms two charged layers with a separation of several

angstroms – the distance from the electrode surface to the

center of the ion layer .

The double layer capacitance is the result of charge separation

in the interface.

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Since capacitance is

proportional to the surface

area and the reciprocal of the

distance between the two

layers, high capacitance

values are achieved.

C = k A / d

Where, C – capacitance,

k- Dielectric constant of

medium

A - area of the plate

d- Distance between the plates

SUPERCAPACITOR

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Using activated carbon which has large surface area for

electrodes, enables EDLC to have high capacitance.

SUPERCAPACITOR

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ACTIVATED CARBON

Activated Carbons are the most powerful adsorbents known.

It is basically a solid material consisting mainly of pure carbon.

A characteristic feature is its porous structure and the resulting

immense surface area which may be as large as 1500 m2/gm.

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ACTIVATED CARBON

Activated carbons work on the principle of adsorption.

Adsorption is an interfacial process involving the collection of

gaseous or solute components on the surface of adsorbent solids.

Adsorption is thus a physical process, i.e. the substances adsorbed

on the solid do not undergo any chemical reaction with the latter.

The adsorbing solid is referred to as adsorbent and the substance

to be adsorbed from the liquid or the gas phase as the solute is

referred to as adsorbate.

The adsorption power and rate is determined by the kind of

activated carbon, the particle size, the pore size and its

distribution.

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The vast increases in capacitance achieved by

supercapacitors are due to the combination of:

(i) an extremely small distance that separates the opposite

charges, as defined by the electric double-layer;

(ii) highly porous electrodes that embody very high

surface-area.

variety of porous forms of carbon are currently preferred

as the electrode materials because they have

•exceptionally high surface areas,

•relatively high electronic conductivity, and

•acceptable cost.

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Electrode material characteristics

The attraction of carbon as a supercapacitor electrode

material arises from a unique combination of chemical

and physical properties, namely:

• high conductivity,

• high surface-area range

• good corrosion resistance,

• high temperature stability,

• controlled pore structure,

• relatively low cost.

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GREEN TECHNOLOGY SUPER CAPACITORS

Activated carbon used is unsustainable and expensive.

Biochar is viewed as a green solution to the activated carbon

currently used in super capacitor electrodes.

Unlike activated carbon, biochar is the byproduct of the pyrolysis

process used to produce biofuels and it is nontoxic and will not

pollute the soil when it is tossed out.

Biochar costs almost half as much as activated carbon, and is

more sustainable because it reuses the waste from biofuel

production, a process with sustainable intentions to begin with.

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