Slide 1 - Course Notes - McMaster University by l62idC8

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									ADVANCED ELECTRODE MATERIALS FOR
ELECTROCHEMICAL SUPERCAPACITORS


       DEEPAK KUMARAPPA


   SUPERVISOR : DR. ZHITOMIRSKY

            MALTS #701
             29, April 2011

                                  1
            OUTLINE

Introduction
Literature review
Problem formulation
Approach and methodology
Results and discussion
Conclusions

                            2
              Applications
Hybride electric vehicle
                             Phone




                             LED driver




                                          3
    Advantages of supercapacitors
    (when compared to batteries)
                               Capacitance:
• High power density
                                    dQ     dV
• Possibility of fast            C    i/
                                    dV     dt
  recharging                   Energy:
• Large cycling capability              1
                                     E  CV 2

  (up to 106 cycles)                    2
                               Power:
• Excellent reversibility                  V2
                                     P
• Longer lifetime                       4  ESR
                             V:   voltage
                             ESR: equivalent series resistance
                                                           4
     Two basic charge-storage mechanisms

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

                                                +                                  -
                 - + -+                                                -       X
          e-+        +- +
                + - ++ - -                  e-  +      +           X                   -
                                                                                       X
                 -
          e-+         -- +                  e- +       +               -           -
            +    - - +- ++                                         X       -   X
          e-
                -- - + +                    e- +       +           -       X
            +                                                    X             -
           -           + +                             +                       X
          e+     -                          e-
                                                                                       5
          Materials science aspects
    Examples of materials and capacitance

•   RuO2                           720 F/g
•   MnO2.H2O                       700 F/g
•   Conductive Polymers      400 – 500 F/g
•   SnO2                           285 F/g
•   NiO                            280 F/g
•   In2O3                          190 F/g
•   Co3O4                          164 F/g

                                             6
              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


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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                Forms dihydromer dication
        of anodic potential

     Different resonance forms                               3. Stabilization




Greater unpaired electron density in α-position   Forms aromatic dimer on losing two protons
                                                                                         8
Electropolymerization of Polypyrrole
           4. Oxidation of dimer




   Dimer                   Dimer cation radical


              5. Formation of trimer




                                                  Trimer
                                                           9
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
                                                                         10
      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

                                                   11
        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
                                                                         12
Strong adhesion in water and aqueous solutions of metal salts
         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) 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          13
               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
                                                                                      14
                      Objectives
• Development of electropolymerization method for the
  fabrication of PPY films on SS using new anionic additives




           Chromotropic acid (CHR)          Gallic acid


• 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
                                                                 15
  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
                                         16
 Approach and methodology
Selected additive         Suggested Complexation mechanism




                                SS



Chromotropic acid (CHR)




                           SS



     Gallic acid
                                                      17
                  Methodology
     Fabrication of Ppy film on Stainless steel
  Pyrrole + Additive
                                    SSt   Pt
                                   +           -
                   Galvanostatic
       Water
       H2O

                               Electropolymerization   Ppy film on
                                                        Substrate
Characterization
• SEM
• Electrochemical testing
    – Cyclic Voltammetry (CV)
    – Electrochemical Impedance
      Spectroscopy (EIS)
                                                                     18
  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
                                                                     19
             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
                                                                              20
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
                                                                       21
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    22
Optimization of CHR and Pyrrole concentrations




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


                                                                      24
 Results and Discussion
  Cyclic Stability            Cyclic Voltammetry
50mM CHR and 150mM Pyrrole
                                              1
                                             1000




            Mass - 147 μg
      scan rate - 50 mV s-1




                                                    25
Results and Discussion
                    Gallic Acid
         50mM Gallic acid and 250mM Pyrrole

Deposition mass Vs Time                 Cyclic Voltammetry


                                   Mass - 116 μg




                                       Electrolyte:0.5M Na2SO4




                                                             26
 Results and Discussion
           50mM Gallic acid and 250mM Pyrrole

        EIS                       Scan Rate Vs Specific Capacitance

83 μg
                   188 μg
                                                a - 83 μg
                                                b - 116 μg
        116 μg                                  c - 188 μg




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                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.
                                                       28
    Acknowledgements

 My Supervisor, Dr. Zhitomirsky

 Steve Koprich, Canadian Centre for
 Electron Microscopy, McMaster
 University

All my group members


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Thank You



            30
Electropolymerization of Polypyrrole
          6. Electro-oxidation of trimer




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