ADVANCED ELECTRODE MATERIALS FOR ELECTROCHEMICAL SUPERCAPACITORS

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

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

6. RuO2 720 F/g MnO2.H2O700 F/g Conductive Polymers 400 – 500 F/g SnO2 285 F/g NiO 280 F/g In2O3 190 F/g Co3O4 164 F/g Materials science aspectsExamples of materials and capacitance

7. Polypyrrole High conductivity Excellent chemical stability High Specific Capacitance - 400 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, 29,283-293 1. Oxidation of monomer 2. Coupling between radicals Forms cation radical on application of anodic potential Forms dihydromer dication Different resonance forms 3. Stabilization Forms aromatic dimer on losing two protons Greater unpaired electron density in α-position

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 Proposedsolution 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. 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 dopamine benzoic acid 1-hydroxybenzoic acid 3,5-dihydroxybenzoic acid gallic acid chromotropic acid (CHR) K. Wu, Y. Wang, I. Zhitomirsky, J. Colloid and Interface Science 352 (2010) 371-378 Y. Wang, I. Zhitomirsky, Colloids and Surfaces A 369 (2010) 211-217 • 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) 371-378 Y. Wang, I. Zhitomirsky, Colloids and Surfaces A 369 (2010) 211-217 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 Gallic acid Chromotropic acid (CHR)

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

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

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

23. Optimization of CHR and Pyrrole concentrations 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 50mM CHR & 150mM Pyrrole 5mM CHR & 50mM Pyrrole 15mM CHR &100mM 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 50mM CHR and 150mM Pyrrole 1 1000 Mass - 147 μg scan rate - 50 mV s-1

26. Results and Discussion Gallic Acid 50mM Gallic acid and 250mM Pyrrole Cyclic Voltammetry Deposition mass Vs Time Mass - 116 μg Electrolyte:0.5M Na2SO4

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