1. ADVANCED ELECTRODE MATERIALS FOR ELECTROCHEMICAL SUPERCAPACITORS
DEEPAK KUMARAPPA
SUPERVISOR : DR. ZHITOMIRSKY
MALTS #701
29, April 2011

2. OUTLINE Introduction Literature review Problem formulation
Approach and methodology
Results and discussion
Conclusions

3. Applications
Hybride electric vehicle
Phone
LED driver

4. Advantages of supercapacitors (when compared to batteries)
Capacitance:
Energy:
Power:
V: voltage
ESR: equivalent series resistance
High power density
Possibility of fast recharging
Large cycling capability
(up to 106 cycles)
Excellent reversibility
Longer lifetime

5. Two basic charge-storage mechanisms
Double-layer capacitance
Pseudocapacitance
(Activated carbon)
(Metal oxides & Conducting Polymers)
Capacitance arises from charge separation at an electrode/electrolyte interface
Utilize the charge-transfer pseudocapacitance arising from reversible Faradaic reactions occurring at the electrode surface - +
5–10 Å
Current
Current - + + + X- e- e- e- e- e- e- e- e-

6. Materials science aspects Examples of materials and capacitance
RuO F/g
MnO2.H2O F/g
Conductive Polymers – 500 F/g
SnO F/g
NiO F/g
In2O F/g
Co3O F/g

7. Polypyrrole High conductivity Excellent chemical stability
High Specific Capacitance F/g
(noble current collectors!)
Large voltage window
Corrosion protection of current collectors
Flexibility
Light weight

8. Electropolymerization of Polypyrrole
Diaz’s mechanism
Said Sadki et al., Chem. Soc. Rev., 2000, 29,
1. Oxidation of monomer
2. Coupling between radicals
Forms cation radical on application of anodic potential
Forms dihydromer dication
Different resonance forms
3. Stabilization
Greater unpaired electron density in α-position
Forms aromatic dimer on losing two protons

9. Electropolymerization of Polypyrrole
4. Oxidation of dimer
Dimer
Dimer cation radical
5. Formation of trimer
Trimer

10. Electropolymerization of Polypyrrole
6. Final polymer product
On continues propagation of above sequence,
final polymer product is obtained
Electropolymerization doesn’t give neutral non-conducting polypyrrole
but its oxidized conducting form (doped)
Final polymer chain has a positive charge which is counter balanced by anion
Films obtained consists of 65% polymer and 35% anion by weight

11. Problem related on anodic electropolymerization on SS
Anodic dissolution of SS substrate at Epa prevents film formation
Proposed solution
W. Su et al., J. Elec. Acta 46 (2000) 1-8
Oxalate additive
Passivation of SS substrate is established
Disadvantages for Supercapacitors
Formation of resistive Iron(II) oxalate layer
Poor adhesion

12. Mussel-Inspired Surface Chemistry
Literature related to proposed approach
Mussel-Inspired Surface Chemistry
J.H. Waite, Nat, Matter. 7 (2008) 8
Dopamine forms strong bonds with metals and oxides
Strong adhesion in water and aqueous solutions of metal salts

13. Literature related to proposed approach
benzoic acid
1-hydroxybenzoic acid
dopamine
gallic acid
3,5-dihydroxybenzoic acid
chromotropic acid (CHR)
K. Wu, Y. Wang, I. Zhitomirsky, J. Colloid and Interface Science 352 (2010)
Y. Wang, I. Zhitomirsky, Colloids and Surfaces A 369 (2010)
Presence of adjacent OH group bonded to aromatic ring in dopamine and gallic acid enhances the adsorption of molecules on the oxide particles
Strong adsorption of CHR on oxide particles was observed

14. Fundamental studies of absorption
K. Wu, Y. Wang, I. Zhitomirsky, J. Colloid and Interface Science 352 (2010)
Y. Wang, I. Zhitomirsky, Colloids and Surfaces A 369 (2010)
Conjugate bond provides high conductance & electron transfer mediation 14

15. Objectives
Development of electropolymerization method for the fabrication of PPY films on SS using new anionic additives
Investigation of kinetics of deposition and deposition mechanism
Optimization of bath composition and deposition parameters
Investigation of electrochemical properties of PPY films for application in electrochemical supercapacitors
Chromotropic acid (CHR)
Gallic acid

16. Suggested role of anionic additives
Approach and methodology
Suggested role of anionic additives
Anionic doping of conducting polymer during electropolymerization
Improves adhesion and reduces anodic dissolution of stainless steel due to complexation with metal ions
Act as electron transfer mediator

17. Approach and methodology
Selected additive
Suggested Complexation mechanism SS
Chromotropic acid (CHR) SS
Gallic acid

18. Electropolymerization
Methodology
Fabrication of Ppy film on Stainless steel
H2O
Water
Pyrrole + Additive
Ppy film on Substrate
Electropolymerization
Galvanostatic - +
SSt Pt
Characterization
SEM
Electrochemical testing
Cyclic Voltammetry (CV)
Electrochemical Impedance Spectroscopy (EIS)

19. Results and Discussion
Galvanostatic behavior
Oxalic acid and Pyrrole
5mM CHR and 50 mM Pyrrole
W. Su et al., J. Elec. Acta 46 (2000) 1-8
No Induction time is required
Good adhesive film is formed

20. Results and Discussion
Deposition mass Vs Time
5mM CHR and 50mM Pyrrole
Pyrrole without additive
Pyrrole + CHR
Current density is 0.7 mA cm-2
Mass of the film can be controlled by deposition time

21. Cyclic Voltammetry [Ppy]f + [A-]s [Ppy·+/A- ]f + e-
5mM CHR & 50mM Pyrrole
15mM CHR and 150mM Pyrrole
Electrolyte:0.5M Na2SO4
[Ppy]f + [A-]s
[Ppy·+/A- ]f + e-
Charging
Discharging
A-: Anions of electrolyte

22. Electrochemical Impedance Spectroscopy (EIS)
5mM CHR and 50mM Pyrrole
104 μg
227 μg
104 μg
227 μg
Limited depth of ion penetration
Pore size
Mobility of ions

23. Optimization of CHR and Pyrrole concentrations
Conc. of CHR (mM)
Conc. of Pyrrole (mM)
Specific Capacitance (F/g) 5 50
206
100
228
150
250 15
302
341
a – 5mM CHR & 50mM Pyrrole
b – 5mM CHR & 100mM Pyrrole
e – 15mM CHR & 150mM Pyrrole
f – 50mM CHR & 150mM Pyrrole
Film mass is approximately 100 μg
Scan rate is 2 mV/s

24. SEM Analysis PPY particles are uniformly distributed
5mM CHR & 50mM Pyrrole
15mM CHR &100mM Pyrrole
50mM CHR & 150mM Pyrrole
PPY particles are uniformly distributed
Porosity of the film increases with increase in CHR and
Pyrrole concentration
Porous structure improves the ions accessibility into the film pores

25. Results and Discussion
Cyclic Stability
Cyclic Voltammetry
Mass μg
scan rate - 50 mV s-1
50mM CHR and 150mM Pyrrole 1
1000

26. Results and Discussion
Gallic Acid
50mM Gallic acid and 250mM Pyrrole
Deposition mass Vs Time
Cyclic Voltammetry
Mass μg
Electrolyte:0.5M Na2SO4

27. Results and Discussion
50mM Gallic acid and 250mM Pyrrole
EIS
Scan Rate Vs Specific Capacitance
83 μg
116 μg
188 μg
a - 83 μg
b μg
c μg

28. Conclusions
Electropolymerization method has been developed for the fabrication of PPY coatings on stainless steel
The electropolymerization mechanism in the presence of CHR and Gallic acid has been investigated.
Films prepared from CHR showed better capacitive behavior than the one prepared from Gallic acid.
The highest specific capacitance was 341 F/g when CHR is used as additive at optimized deposition conditions.
The films prepared by the electropolymerization method are promising materials for application in electrochemical supercapacitors using low cost stainless steel current collectors.

29. Acknowledgements My Supervisor, Dr. Zhitomirsky
Steve Koprich, Canadian Centre for Electron Microscopy, McMaster University
All my group members

30. Thank You

31. Electropolymerization of Polypyrrole
6. Electro-oxidation of trimer