electrochemical impedance & morphologic study of poly( propylenedioxythiophene) -thin films on...
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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
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C4H9 C4H9
n
S
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n
m
n
S
RR
34
ProDOT-(Bu)2ProDOT-(Me)2
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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)
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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
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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
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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
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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
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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
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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
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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)
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C4H9 C4H9
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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
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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
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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
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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
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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
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Cycle Effect of PProDOT-Bu2/SCFME
BODE MAGNITUDE
Cdl : 1 / IZimI
Cycle Effect of PProDOT-Bu2/SCFME
NYQUISTCLF : 1/ 2π f Zim
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Cycle Effect of PProDOT-Bu2/SCFME
EQUIVALENT CIRCUIT
BODEPHASE
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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
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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
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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
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