Super capacitors

1. CARBON NANOTUBE
SUPERCAPACITORS

2. ABSTRACT
• The supercapacitors are advanced electrochemical energy storage devices having characteristics
such as high storage capacity, rapid delivery of charge, and long cycle life. Polypyrrole (ppy) e an
electronically conducting polymer, and carbon nanotubes (CNT) with high surface area and
exceptional electrical and mechanical properties are among the most frequently studied advanced
electrode materials for supercapacitors. The asymmetric supercapacitors composed of ppy/CNT
composite electrodes offer complementary benefits to improve the specific capacitance, energy
density, and stability. This article presents an overview of the recent technological advances in
ppy/CNT composite supercapacitors and their limitations. Various strategies for synthesis and
fabrication of ppy/CNT composites are discussed along with the factors that influence their
ultimate electrochemical performance.
• Keywords: carbon nanotube, electrochemistry, energy storage, polypyrrole,
supercapacitor

3. INTRODUCTION
• 21st century is witnessing a global revolution in the pursuit for Alternative energy resources such as
wind, solar, hydro, geothermal, and biomass etc.
• At present, batteries and capacitors are the most common devices for electrical energy storage.
• An ideal device should possess greater storage capacity, high power and energy densities and excellent
cyclabilty.
• Electrochemical supercapacitors helps batteries and capacitors to operate at high specific power
• Supercapacitors offer charging/discharging and long lifecycle, high energy density and Eco-friendly.

4. SUPERCAPACITORS: TYPES
• Supercapacitor: It also called as ultracapacitor which has a high capacity capacitor with a capacitance
value much higher than other capacitors but with lower voltage limits.
• It typically stores 10-100 times more energy per unit volume/mass.
• Based on storage supercapacitors are classified in to three types

5. Electric double layer capacitors (EDLC)
• EDLC involves in non faradaic processes i.e. the charge storage is achieved by the adsorption of
ionic species and charged particles at the interface.
• EDLC are based on highly porous materials such as activated carbons with high specific area
which allows greater electrolyte accessibility and thus a greater energy storage.

6. PSEUDO & ASYMETRIC CAPACITORS
• PSC are the one which involve highly reversible faradaic processes i.e. charge storage is achieved by
superficial redox reactions between electrochemically active materials and the electrolyte.
• These are based on metal oxides/hydroxides and exhibit high specific capacitance than EDLC.
• Asymmetric supercapacitors are also called as hybrid capacitors which consists of two or more
different electrode materials with advantages of enhancing the operation voltage and energy density.
• These are developed in such a way in order to over come limitations of both EDLC & PSC such as low
specific capacitance , low conductivity and poor cyclability.

7. CNT IN SUPERCAPACITORS
• Along with the activated carbons and metal oxides/hydroxides, electronic conducting polymer
(ECP) and carbon nanotubes (CNT) have been used as the electrode materials.
• CNT exhibit high inherent electrical and thermal conductivity, flexibility, excellent chemical,
thermal, and mechanical stability, good corrosion resistance, and large surface area polarizability.
• CNT have low specific capacitance in the range of 4-135 F/g
• ECP are attractive materials for supercapacitor electrodes due to low cost, good electrical
conductivity, and high pseudo capacitance.
• ECP have very high theoretical capacitance such as 620 F/g for polypyrrole

8. CNTD…….
• Ppy has been deposited on pure and/or functionalized CNT to yield hybrid electrode materials
with superior electrochemical performance through a combination of the EDLC and high
conductivity of CNT and high pseudo capacitance of redox-active ppy.
• PPy/CNT composite based ASC has an exceptionally high value of 890 F/g in 1.0 KCL
electrolyte

9. SYNTHESIS OF PPY/CNT
• Ppy/CNT composites are predominantly prepared as ppy coating on CNT surface using different
procedures based on
(a) chemical methods
(b) electrochemical processes involved in the polymerization of PPy on CNT
surface.

10. CHEMICAL METHODS
• Chemical methods for synthesis of ppy usually involve the use of oxidants such as ferric chloride,
ferric perchlorate, and ammonium peroxydisulfate. CNT are dispersed into the reaction mixture along
with the monomer (pyrrole), the oxidant (e.g. FeCl3),and various additives to form PPy/CNT
composites.
• CNT surface modification has been achieved by oxidation in concentrated acids or acid mixtures
which results in the
• Formation of hydroxy-, carboxylic acid-, and other oxygen containing groups on CNT surface. These
surface functional groups electrostatically stabilize CNT in solution and may also act as the nucleation
sites for polymer coating on CNT surface

11. CONTD…
• Air plasma treatment is an alternative option for surface modification of CNT, which yields oxygen- as
well as nitrogen containing groups on CNT surface.
• Electrical conductivity of CNT and graphene are believed to improve through substitutional doping of
carbon with hetero elements such as nitrogen, boron, or sulfur.
• Air plasma treated CNT may enhance the electrochemical performance of resulting PPy/CNT
composites.
• It is confirmed that concentrated acid and air plasma treatments of CNT remarkably enhance their
interfacial compatibility with PPy and super capacitive performance of the resulting PPy/CNT
composite electrodes.

12. AIR PLASMA TREATMENT

13. ELECTROCHEMICAL METHODS
• A typical electrochemical procedure involves potentiostatic or galvanostatic deposition of pyrrole
from an electrolyte solution on the surface of CNT.
• Electrode potential, current density, and/or deposition time can be varied during the electro
deposition to control the amount of Ppy deposited on CNT.
• In electrochemically prepared PPy/CNT composite film a thin layer of amorphous PPy is
deposited on the outer surface of crystalline CNT which offers the fast diffusion and migration of
ions, thereby enhancing the PPy/CNT supercapacitor's performance.

14. CNTD…..
• The higher specific capacitance of pulse electrodeposited ppy/CNT composite electrodes is
attributed to the higher surface area and porosity of resulting ppy/CNT films, which allow
greater electrolyte accessibility

15. CNTD…

16. RESULTS

17. CNTD…

18. LIMITATIONS
• Ppy is known to exhibit poor cyclability, which is primarily due to its large volume
transformations during repetitive redox (charge/discharge) cycles.
• PPy/CNT composite super capacitors can retain up to 95% capacitance after 10000 cycles, which
is promising for practical application which is yet to improve the cyclability of PPy/CNT
composite super capacitors.
• Chemical oxidative polymerization of PPy with CNT from aqueous solution may suffer from
poor dispersion of CNT, PPy aggregation, and increased resistance owing to weaker CNT
interconnection

19. CONCLUSION
• To overcome these problems and to achieve better interfacial connections between ppy and CNT
CNT functionalization is required that has been mostly achieved through concentrated acid
treatment.
• Electrochemical deposition methods cannot be scaled-up for mass production of ppy/CNT
composites due to complicated procedures.
• It is essential to identify these charging mechanisms and their equilibrium in order to fully
understand and exploit the capacitive properties of PPy/CNT composites.
• PPy/CNT composites make high performing electrochemical energy storage devices, but enough
is to be done to meet the commercial requirements of super capacitors which is still under
research.

20. QUERIES????

21. THANK YOU…