Electrochemical Impedance & Morphologic Study of

Poly( Propylenedioxythiophene) -Thin Films on Carbon Fiber

Prof.Dr.A.Sezai SARACDepartment of Chemistry & Polymer Science

& Technology

ISTANBUL TECHNICAL UNIVERSITY

Energy storage(batteries, supercapacitors)

Electrochromic devices (smart Windows, mirrors, IR and microwave shutters)

Antistatic coatings (displays, flat TV screens)

Semiconductor devices (Solar Cells)

Corrosion Protection

Mechanical actuators

Bio applications (drug delivery systems, artificial muscles, biosensors)

Conducting Polymer Conducting Polymer (Nano)(Nano)/ Carbon Fiber(Micro)

SupercapacitorsSupercapacitors(Electrochemical (Electrochemical capacitors)capacitors)

Supercapacitors store the electric energy in an electrochemical double layer (Helmholtz Layer) formed at a solid / electrolyte interface.

AdvantagesHigh energy density& rates of charge&discharge Little degradation-longer cycle lifesmall chemical charge transferGood reversibility Low toxicity High cycle efficiency (95% >)

AdvantagesHigh energy density& rates of charge&discharge Little degradation-longer cycle lifesmall chemical charge transferGood reversibility Low toxicity High cycle efficiency (95% >)

X X

X

X

-e-

Epa

X X

X

H

H

2 + 2H

X

X -e-

Epa X

X H+

X

X

X

H

H

X

X

XX

+ 2H

Electropolymerization mechanism of 5-membered heterocycles

Cyclic Voltammetry (CV)

Monomer Free

Polymer Electrogrowth

extremely useful for studying electrode reaction mechanisms &electropolymerization

Red ↔Ox + e-→X

doping; reduction or oxidation. Oxidation leaves "holes" in the form of positive charges that can move along the

chain

Electrochemical Impedance Spectroscopy

(AC) The excitation signal , expressed as a function of time , has the form

E(t) = E0 cos (wt)

In a linear system, the response signal , It , is shifted in phase (Ф) and has a different amplitude

I(t) = I0 cos (wt - Ф )

= Zo [ cos(wt) / cos(wt – Ф ) ] Using EULER’s relationship

Exp ( j Ф ) = cos Ф + jsin Ф

Z = Z0(cos Ф + jsin Ф )

Z = E(t) / I(t)

DC ohms law R= E/I

Poly(3,4-alkylenedioxythiophene) Derivatives

Poly(3,4-dialkylthiophene)

Substitution at the 3- and 4- positions

LONGER CONJUGATION LENGTHMORE ORDERED POLYMERS

LOW EoxSTABLE OXIDIZED FORM

STERIC INTERACTIONS INCREASING DEGREE OF CONJUGATIONCONDUCTIVITY

Alkyl substitution to the monomer, lowers the EOX

J.Roncali,Chem.Rev.1997,97,173

S

OO

C4H9 C4H9

n

S

OO

n

m

n

S

RR

34

ProDOT-(Bu)2ProDOT-(Me)2

S

OO

n

CH3 CH3

EXPERIMENTAL -ELECTROCHEMICAL

Cyclic Voltammetric (CV)Coating: 10 mM ProDOT-(Bu)2 in

0,1 M NaClO4/ACN & Bu4NPF6/ACN at diff.scan rates (mV s-1 )

0,0 V – 1,6 V

3 ELECTRODE SYSTEM

W.E. : CFSE , ITO ,PtR.E. : Ag wire (checked aginst [FcII(CN)6]4- [FcIII(CN)6]3- + e-)C.E. : Pt wire

Electrochem.Impedance Spectroscopy (EIS) 0,1 M NaClO4/ACN 100 kHz -10 mhz

Depending on the situation, forces that are measured in AFM include mechanical contact force, Van der Waals forces, capillary forces, chemical bonding, electrostatic forces, magnetic forces, solvation forces etc. --the three dimensional topography

8

Atomic Force Microscopy (AFM)NON-CONTACTNON-CONTACT

Atomic Force Microscopy (AFM)Atomic Force Microscopy (AFM)

S

OO

C4H9 C4H9

n

0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6-200

0

200

400

600

800

-0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2

-2000

-1000

0

1000

2000h

a

h

a

Cu

rre

nt

de

ns

ity

/ A

/cm

2

Potential / V

0 50 100 150 200 250 300 350 400

-2500

-2000

-1500

-1000

-500

0

500

1000

1500

2000

2500

Cu

rre

nt

de

ns

ity

/

A/c

m2

Scan rate / mV s-1

Oxidationpeak1 Reductionpeak1 Oxidationpeak2 Reductionpeak2

5mM ProDOT-Me2 deposited at 100 mV/s, 10cycle in 0.1 M Bu4NPF6/ACN5mM ProDOT-Me2 deposited at 100 mV/s, 10cycle in 0.1 M Bu4NPF6/ACN

EDX results of coatings

S

OO

n

CH3 CH3

100 mV/s 100 mV/s EDX of film EDX of film

Bandgap- of film on ITOBandgap- of film on ITO

Cyclic Voltammetric film growth Cyclic Voltammetric film growth

S

OO

n

CH3 CH3

SCAN RATE EFFECT400 mV/s

SCAN RATE EFFECT400 mV/s

uncoated

SEM & AFM Electrocoated 2,2-Dimethyl-3,4 Propylenedioxythiophene on CFMEin 0.1 M Bu4NPF6/ACN at scan rate: 400 mV/s, 10 cycle.

SEM & AFM Electrocoated 2,2-Dimethyl-3,4 Propylenedioxythiophene on CFMEin 0.1 M Bu4NPF6/ACN at scan rate: 400 mV/s, 10 cycle.

SEM & AFM Electrocoated 2,2-Dimethyl-3,4 Propylenedioxythiophene on CFME 20 mV/s & 10 cycle 20 mV/s 20 mV/s

S

OO

n

CH3 CH3

uncoated CF

SEM and AFM of PProDOT-(Me)2/CFME coated at 10 mV/s and 10 cycle 10 mV/s 10 mV/s

Sarac AS,Schulz B,Gencturk A.,GilsingHD ,Surface Eng. (2008) in Press

SEM picture of PProDOT-(Me)2/CFME in 0,1 M Bu4NPF6/ACN scan rate:100 mV/s ,10 cycle, 2 different magnifications

100 mV/s 100 mV/s

S

OO

n

CH3 CH3

Cyclovoltammetric (C = charge density/scan rate) &• Nyquist plots (at low frequency) in monomer free solution &(polymer film obtained at 10 cycle, 10 mM monomer, 0.1 M Bu4NPF6/ACN).

Capacitance vs scan rate

Sarac AS,Schulz B,Gencturk A.,GilsingHD ,Surface Eng. (2008) in Press

20th cycle coated CFME

40th cycle

uncoated CFME

40th cycle

PProDOT-(Me)2 in 0,1 M Bu4NPF6/ACN

S

OO

n

CH3 CH3

100 mV/s

DIFFERENT CHARGE (CYCLE NO)

5 10 15 20 25 30

100

150

200

250

300

350

400

450

500

550

600

0 20 40 60 80 100 120

0.50

0.55

0.60

0.65

0.70

0.75

0.80

Pot

entia

l / V

Time / s

15s

5mM ProDOT-Me2 deposited at 100 mV/s in 0.1 M Bu4NPF6/ACN

Capacitance vs scan no

Sarac AS, Gilsing HD, Gencturk A, et al. Prog.Org.Coat. 60 (2007) 281

parameters of the model- EIS• 1.Bulk Electrolyte resistance (Rs)

• 2.Double layer capacitance(Cdl)

• 3.Polarization resistance(R1)

• 4.Charge transfer resistance(R2)

• 5.Warburg impedance(W)

• 6.CF & film capacitance

• 7.Constant phase element (Q)

. • Ates M,Castillo J,Sarac AS, Schuhmann W, Microchim Acta 160(2008)247• Sarac AS ,Sipahi M, Parlak EA ,Gul A , Ekinci E,Yardim F , Prog Org.Coat. 62 (2008) 96• SaracAS, Sezgin S, AtesM, Turhan CM, Parlak EA, Irfanoglu B , Prog. Org. Coat.

62( 2008) 331

EQUIVALENT CIRCUITR(C(R(Q(RW))))(C(R))

Cdl Ccf

Rs

R2

R1

RCF

(Electrochemical deposition is performed at different molarities of ProDOT-Me2 at 100 mV/s, 20 cycle in 0.1 M Bu4NPF6/ACN).

E=0.2V E=0.4V E=0.7V E=1.0V E=1.3VRs / Ohm 1850 1852 1851 1851 1860Cdl /μ F 97.82 111.5 103.9 69.32 9.617x10-12

R1 / kOhm 2.964 3.449 14.860 0.390 0.0011Q / Yo/ μS s-

n1.501x10-2 6.497x10-2 5.057x 10-3 2.548x10-2 8.891x10-2

n 0.8932 0.96 1 1 0.9818R2 / kOhm 723 935.6 9.998 98.99 1296W / Yo/ S s-n 2.532x10-6 1.222x 10-6 2.966x 10-6 2.942x10-6 9.046x10-6

CCF / μF 0.205 1.10 0.286 2.50 0.2404RCF / Ohm 20.9 25.36 28.11 44.15 26.24Chi Squared (χ2) 3.57x10-5 4.87x 10-5 3.81x10-5 3.66x10-5 5.09x10-5

Potential Potential dependence dependence the parameters calculated from the model

S

OO

n

CH3 CH3

Rs, the bulk solution resistance of the polymer and the electrolyte, Cdl, double layer capacitance, R1 is the resistance of the electrolyte.(Polarization) R2 is the charge transfer, and W is the Warburg impedance of the polymer.

Poly(3,4-alkylenedioxythiophene) Derivatives

2,2 -dibutylpropylene dioxythiophene (PProDOT(Bu)2)

S

OO

C4H9 C4H9

S

OO

C4H9 C4H9

n

PProDOT-(Bu)2/0,1 M Bu4NPF6 /ACN PProDOT-(Bu)2/0,1 M Bu4NBF4/ACN

Atomic Force Microscopy (AFM)&SEMElectrolyte effect

A.S. Sarac, A. Gencturk, H.D. Gilsing, B. Schulz,C.M. Turhan, J.NanoSci.& Nanotech. 2008- In press

PProDOT-(Bu)2/0,1 M Et4NClO4 /ACN

Atomic Force Microscopy (AFM)

PProDOT-(Bu)2/0,1 M LiClO4/ACN

S

OO

C4H9 C4H9

n

Electrolyte effect

23

PProDOT-(Bu)2/0,1 M NaClO4 /ACN

Atomic Force Microscopy (AFM)

A.S. Sarac, A. Gencturk, H.D. Gilsing, B. Schulz,C.M. Turhan, J.NanoSci.& Nanotech. – 2008- In press

S

OO

C4H9 C4H9

n

0.1 M NaClO4/ACN 10 cycle 100 mV/sNaClO4 /ACN 30 cyc

100 mV/s

24

Atomic Force Microscopy (AFM)Electrolyte

Sarac, AS. Gencturk, H.D. Gilsing, B. Schulz,C.M. Turhan, J.NanoSci.and Tech. – 2008- in press

0 1 5

0,0

0,5

1,0

1,5

2,0

2,5

3,0

3,5

30

35

40

45

50

55

60

Cdl

Et4NClO

4

Bu4NBF

4

LiClO4

R.M

.S. /

nm

Cd

l / m

F

Increase in radius of CF / m

R.M.S. Roughness

NaClO4

Bu4NPF

6

Cycle Effect of PProDOT-Bu2/Single CFME

1st CYCLE

S

OO

C4H9 C4H9

n

Randless Sevcik Equation : ip = (2.69x105) n3/2ACD1/2γ1/2

Cycle Effect of PProDOT-Bu2/SCFME

n : number of electrons, ν scan rate (V / sec) F :Faraday’s constant (96485 C / mol)

A : Electrode area (cm2) R : Universal gas constant (8.314 J / mol K)

T : Absolute temperature (K), and D is the analyte’s diffusion coefficient (cm2/sec).

1st CYCLE

Cycle Effect of PProDOT-Bu2/SCFME3 CYCLES 5 CYCLES

(Scan rate)1/2 Scan rate (Scan rate)1/2 Scan rate

Cycle Effect of PProDOT-Bu2/SCFME

10 CYCLES 15 CYCLES

(Scan rate)1/2 Scan rate (Scan rate)1/2 Scan rate

10 CYCLES 15 CYCLES

Cycle Effect of PProDOT-Bu2/SCFME20 CYCLES

Sarac AS, Gilsing HD, Gencturk A, et al. Prog. Org. Coat. 60 (2007) 281

S

OO

C4H9 C4H9

n

Cycle Effect of PProDOT-Bu2/SCFME

AFM

1 cycle 3 cycles 5 cycles

10 cycles 15 cycles 20 cycles

Cycle Effect of PProDOT-Bu2/SCFMESEM 1-3-5 Cycles

Cycle Effect of PProDOT-Bu2/SCFME

SEM 10-15- 20 cycles

Cycle Effect of PProDOT-Bu2/SCFME

EIS

BODEPHASE

Sarac AS, Gencturk A, Schulz B, et al. Journal of Nanoscience and Nanotechnology 7 ((2007 )3543

S

OO

C4H9 C4H9

n

Cycle Effect of PProDOT-Bu2/SCFME

BODE MAGNITUDE

Cdl : 1 / IZimI

Cycle Effect of PProDOT-Bu2/SCFME

NYQUISTCLF : 1/ 2π f Zim

S

OO

C4H9 C4H9

n

Cycle Effect of PProDOT-Bu2/SCFME

EQUIVALENT CIRCUIT

BODEPHASE

S

OO

C4H9 C4H9

n

Cycle Effect of PProDOT-Bu2/SCFMEEQUIVALENT CIRCUIT

BODE

Cycle Effect of PProDOT-Bu2/SCFMEEQUIVALENT CIRCUIT

NYQUIST PLOT

Cycle Effect of PProDOT-Bu2/SCFMEEQUIVALENT CIRCUIT

R(C(R(Q(RW))))(C(R)) Cdl Ccf

Rs

R2

R1

RCF

Cycle Effect of PProDOT-Bu2/SCFME

EQUIVALENT CIRCUITCdl Ccf

Rs

R2

R1

RCF

S

OO

C4H9 C4H9

n

Rs, the bulk solution resistance of the polymer and the electrolyte, Cdl, double layer capacitance, R1 is the resistance of the electrolyte. R2 is the charge transfer, and W is the Warburg impedance of the polymer.

Potential Effect of PProDOT-Bu2/CFSEEQUIVALENT CIRCUIT

Potential Effect of PProDOT-Bu2/CFSE

0.1 – 1.1 V After 1.1 V

Substrate Effect of PProDOT-Bu2

Pt SCFE ITO

Substrate Effect of PProDOT-Bu2BARE Csp / mFcm-2 C dl / mFcm-2

ITO 2.2 x 10-4 0.94Pt 3.9 1.54CF 0.0221 0.13

10 cyc Csp / mFcm-2 C dl / mFcm-2

ITO 8.85 6.45Pt 83.00 164.00CF 45.00 270.00

C sp ctd / C sp bare

C dl ctd / C dl

bare

ITO 402 68

CF 2036 2142Pt 21 106

S

OO

C4H9 C4H9

n

ConclusionEquivalent circuit simulations corresponding to the polymer modified microelectrodes calculated and suggested values of the each component was in good correlation with experimental data.

Typical CV of the polymeric film exhibits very well-defined and reversible redox processes.

Porous nanostructures were obtained with high capacitances

The impedance changes with film thickneses & morphologies, between 0.1 V and 1.4 V.

A potential range was found to be the most suitable condition for the PProDOT-Bu2 modified microelectrodes as supercapacitor

components

acknowlegements

• Dr.B.Schulz – Potsdam University & IDM Teltow Germany

• Dr.Gilsing –IDM Teltow Germany

• M.Turhan –Univ.of Nurnberg &Istanbul Tech Univ• A.Gencturk - Istanbul Tech Univ

Thank you

Istanbul Bosphorous