Influence of Current Density on PolypyrrInfluence of Current Density on Polypyrrole (PPY) Properties ole (PPY) Properties and and Approaching the Electrochemical DeposApproaching the Electrochemical Deposition of Nickel Nanoparticles on PPYition of Nickel Nanoparticles on PPY

Prepared By:

Mark Pynenburg

NSERC-USRA

WATLabs, University Of Waterloo

Ni deposited on ppy (20s at 1.2mA) using Amperometric i-t E=-1.25V, Q=1.92mC t=17.5s

Cu deposited on ppy (1600s at 15uA) using Amperometric i-t E=-1.2V, Q=0.5635mC t=1.3s

OutlineOutline Experimental Objectives.Experimental Objectives. Experimental Setup.Experimental Setup.

Wafer PreparationWafer Preparation Electrochemical Deposition Station.Electrochemical Deposition Station. SEM/AFM ImagingSEM/AFM Imaging

Current Density.Current Density. MotivationMotivation TheoreticalTheoretical DiscussionDiscussion

Nickel Deposition.Nickel Deposition. Pulse Electrodeposition (PED)Pulse Electrodeposition (PED) 22ndnd Deposition Problem Deposition Problem

ConclusionsConclusions Moving ForwardMoving Forward AcknowledgementsAcknowledgements

Experiment ObjectivesExperiment Objectives

To explore the effects of current density oTo explore the effects of current density on ppy film properties.n ppy film properties.

To prepare monoshaped and monosized To prepare monoshaped and monosized nickel nanoparticles on ppy film by electrnickel nanoparticles on ppy film by electrochemical deposition.ochemical deposition.

Experimental SetupExperimental SetupPreparation of Au sputtered 2.5mm X 15mm Si Waf

er:

1. Ultrasonic pre-cut wafers in wash acetone.

2. Rinse wafers with isopropyl alcohol.

3. Bake wafers @ 80C under vacuum. Purging once with nitrogen after ½ hour then under vacuum again for 1 hour.

4. Allow wafers to cool in dry box under nitrogen. Etch surface for 30s using magnetron sputter-coater under 150mTorr Ar with 20mA current. Sputter approximately 100nm Au film using sputter: 4 applications of approx. 25nm each done under 50mTorr Ar with 60 to 80mA current for 120s.

5. Use electrochemical station (potentio/galvanostat) to deposit ppy and metals.

Electrochemical StationElectrochemical StationWorking Electrod

eReferenc

e Electrod

e

Counter

Electrode

VA

Electrochemical Control Module

Au covered Si wafer

Stored in 3M KCl Solution

Computer Display Output

Electrochemical StationElectrochemical Station

Ppy & metal solutions bubbled with N2 or Ar for at least 20 min prior to deposition

Counter Electrode flamed for 30 second

before deposition

Scanning Electron Scanning Electron MicroscopyMicroscopy

Atomic Force MicroscopyAtomic Force Microscopy

Current DensityCurrent DensityMotivationMotivation Electrochemical Synthesis of Polypyrrole: Influence of

Current Density on Structure, K. West et al., Synthetic Metals 55-57 (1993) 1412-1417 Focused on the deposition of ppy in a non-aqueous

environment: 0.5M LiClO4 (electrolyte) in propylene carbonate. Deposited films with current densities between 6.5 uA/cm2 and

3.84 mA/cm2. Identified low current and high current forms. Characterized films with cyclic voltammograms and in situ

spectroscopy (320-1200 nm). Authors’ ConclusionsAuthors’ Conclusions

Current density crucial parameter in determining properties of ppCurrent density crucial parameter in determining properties of ppy.y.

Low current density closer to intrinsic properties of pure ppy. ShLow current density closer to intrinsic properties of pure ppy. Should be used as a reference for investigating effects of changing ould be used as a reference for investigating effects of changing conditions on properties.conditions on properties.

Adding water has little or no influence on properties of this modifiAdding water has little or no influence on properties of this modification but lowers stability.cation but lowers stability.

Lower current density incorporates more anions.Lower current density incorporates more anions.

TheoreticalTheoretical Pyrrole dissolved in solvent with anionic doping salt is oxidizPyrrole dissolved in solvent with anionic doping salt is oxidiz

ed at the surface of an electrode by application of an anodic ed at the surface of an electrode by application of an anodic potential.potential.

As s result of initial oxidation, the radical cation formed reactAs s result of initial oxidation, the radical cation formed reacts with other monomers to form oligomeric products and then s with other monomers to form oligomeric products and then the polymer.the polymer.

Conjugation in the polymer lowers its oxidation potential wrt tConjugation in the polymer lowers its oxidation potential wrt to monomer. Therefore synthesis and anionic doping occur co monomer. Therefore synthesis and anionic doping occur concurrently.oncurrently.

Anion is incorporated into polymer to ensure electrical neutraAnion is incorporated into polymer to ensure electrical neutrality of film.lity of film.

Mechanism is controversial - # of competing schemesMechanism is controversial - # of competing schemes Equation governing thickness of ppy deposition:Equation governing thickness of ppy deposition:

AnF

QMh

ppy

Q = i x t A = .15 to .1875 cm2

Mppy = 67.09 g/molF = 96500C/moln = (2 + .025)p – density (0.967,1.2, 1.5g/cm3?)

PPY Density Determination Using Quasiempirical PPY Density Determination Using Quasiempirical MethodMethod

Polypyrrole Thickness vs Charge Transfered(C)

y = 9076.5x - 8.2208

y = 10224x - 10.549

y = 7887.6x + 7.863

50

70

90

110

130

150

170

190

210

230

7.5E-03 9.5E-03 1.2E-02 1.4E-02 1.6E-02 1.8E-02 2.0E-02 2.2E-02 2.4E-02

Charge (C)

Th

ickn

ess

(nm

)

High Current Density 0.8158mA

Constant Time 20s

Low Current Density 13.598 uA

Linear (High Current Density 0.8158mA)

Linear (Low Current Density 13.598 uA)

Linear (Constant Time 20s)

PPY Density Determination Using PPY Density Determination Using Quasiempirical MethodQuasiempirical Method

AnmF

Mppy

bmxy

mQh

AnF

QMh

ppy

AnF

Mm

ppy

• Used AFM to obtain thickness of films at various points.

• Using the values from the slopes of the graph 1.0224x10-3 to 7.8876x10-4 cm/C. Intercept negligible.

• Assume value of n as either 2 or 2.25 and range of area was from .15 to .1875 cm2.

• Thus able to obtain an upper and lower bound on density ρ = 2.9 to 1.6g/cm3

• Lower number seems more reasonable. Agrees better with literature and previous value.

• Formula doesn’t account for the doping anions.

• Instead of talking about ppy thickness use galvanostatic current and time of polymerization.

DiscussionDiscussion

In the course of the current deposition In the course of the current deposition work discovered factors that may effect work discovered factors that may effect ppy properties:ppy properties: Purity of the monomer solution.Purity of the monomer solution. Age of ppy film when doing subsequent Age of ppy film when doing subsequent

metal deposition.metal deposition.

Variations in PPY due to Variations in PPY due to age of pyrroleage of pyrrole

Larger variation in ppy Larger variation in ppy depositions before depositions before freshly distilling pyrrolefreshly distilling pyrrole

Top old ppy 1600s 15uA Top old ppy 1600s 15uA dep potential varies by dep potential varies by 0.07V0.07V

Bottom fresh ppy 2000s Bottom fresh ppy 2000s 12uA dep potential 12uA dep potential varies by 0.014Vvaries by 0.014V

The effect of PPY age on The effect of PPY age on Cu depositionCu deposition

Cu deposited on ppy using Amperometric i-t E= -1.4V, Q=0.5635mC, t < 1s

Top left ppy 20s/1.2mA, Top right 160s/150uA, left 1000s/24uA

Red day old ppy film

Blue fresh ppy film

Current Density on Cu DepositionCurrent Density on Cu Deposition

Red 20s Red 20s 1.2mA1.2mA

Blue 160s Blue 160s 0.15mA0.15mA

Brown 500s Brown 500s 48uA48uA

Green Green 1000s 24uA1000s 24uA

Navy 2000s Navy 2000s 12uA12uA

Cu deposited on ppy using Amperometric i-t E=-1.4V, Q=0.5635mC t <1s

Current Density on Cu Deposition -1.2V Current Density on Cu Deposition -1.2V Deposition time varied with film Deposition time varied with film type/agetype/age

ppy 160s @ 150uA ppy 320s @ 75uA

ppy 800s @ 30uA ppy 1600s @ 15uA

The trouble with cyclic The trouble with cyclic voltammograms (CVs)voltammograms (CVs)

Six identically deposited ppy films gave vastly different results Six identically deposited ppy films gave vastly different results when CVs done in dep. electrolyte 0.1M NaClOwhen CVs done in dep. electrolyte 0.1M NaClO44

NickelNickel

Observed similar results to Observed similar results to earlier work of Neha and earlier work of Neha and SabrinaSabrina

Both observed ppy 2 step due Both observed ppy 2 step due likely to monomer age which likely to monomer age which may have effected Ni may have effected Ni deposition propertiesdeposition properties

When Ni deposition has When Ni deposition has occurred usually very low occurred usually very low numbersnumbers

Varying pH and potential Varying pH and potential yielded little new informationyielded little new information

NickelNickel

When ppy is reduced the incorporated When ppy is reduced the incorporated perchlorate anions are released according to perchlorate anions are released according to the reaction:the reaction:

(PPy(PPy++ClOClO44--) + e) + e-- PPy PPy00 + ClO + ClO44

--

Metals are to be deposited by reduction.Metals are to be deposited by reduction. Reduction current has two components, one due to Reduction current has two components, one due to

reduction of ppy with simultaneous release of anions reduction of ppy with simultaneous release of anions as counterions illustrated above, and when a as counterions illustrated above, and when a negative enough potential for Ni reduction is negative enough potential for Ni reduction is applied:applied: NiSONiSO44

+2+2 + 2e + 2e Ni Ni00 + xSO + xSO44

NickelNickel

However picture is much more complicated:However picture is much more complicated: Boric Acid is used as a buffer at electrode surface.Boric Acid is used as a buffer at electrode surface. Sulfuric acid is used to acidify medium to supress Sulfuric acid is used to acidify medium to supress

formation of hydroxides.formation of hydroxides. Deposited Ni can act as a catalyst for hydrogen Deposited Ni can act as a catalyst for hydrogen

evolution, different sites on Ni deposit can favour a evolution, different sites on Ni deposit can favour a variety of adsorbants, mechanism of deposition variety of adsorbants, mechanism of deposition complicated.complicated. See papers: “See papers: “Nanocrystalline Copper by Pulsed Nanocrystalline Copper by Pulsed

Electrodeposition”, H. Natter & R. Hempelmann, J. Phys. Chem. Electrodeposition”, H. Natter & R. Hempelmann, J. Phys. Chem. 1996, 100, 19525-19532. and “First Stages of Ni Deposition on 1996, 100, 19525-19532. and “First Stages of Ni Deposition on Vitreous Carbon from Sulfate Solutions”, A. G. Munoz et al., Thin Vitreous Carbon from Sulfate Solutions”, A. G. Munoz et al., Thin Solid Films, 429 (2003) 119-128.Solid Films, 429 (2003) 119-128.

NickelNickel

NickelNickel

Pulse Pulse ElectrodepositionElectrodeposition (PED) (PED)

MotivationMotivation Nanocrystalline Copper by Nanocrystalline Copper by

Pulsed Electrodeposition, H. Pulsed Electrodeposition, H. Natter & R. Hempelmann, J. Natter & R. Hempelmann, J. Phys. Chem. 1996, 100, 19525-Phys. Chem. 1996, 100, 19525-19532.19532.

Use shape of current pulses Use shape of current pulses to influence grain size, to influence grain size, distribution, shape.distribution, shape.

Truncated octahedral Cu Truncated octahedral Cu formed exhibiting self formed exhibiting self organizational behaviourorganizational behaviour

Initial Ni experiments using Initial Ni experiments using PED not as promising. PED not as promising.

Pulse Electrodeposition Pulse Electrodeposition (PED)(PED)

Short (1 to 10ms) Short (1 to 10ms) high current/potential high current/potential pulse followed by pulse followed by long rest (>100ms)long rest (>100ms) High nucleation rateHigh nucleation rate Surface of electrode Surface of electrode

has chance to return has chance to return to equilibriumto equilibrium

Nature of diffusion Nature of diffusion controlled growth controlled growth changedchanged

Ni vs. Cu 2Ni vs. Cu 2ndnd Deposition Deposition

Ni deposition exhibits Ni deposition exhibits behavior not behavior not observed in Cu observed in Cu deposits.deposits.

Often only the first Often only the first deposition leads to deposition leads to and and

Cu close agreement between 1st & 2nd dep.

1st Ni dep.

2nd Ni dep.

ConclusionsConclusions Current density:Current density:

Has an effect on the nature of ppy film as illuHas an effect on the nature of ppy film as illustrated by Cu deposition.strated by Cu deposition. Could be due to better ppy conductivity, greater iCould be due to better ppy conductivity, greater i

ncorporation of anion ncorporation of anion Freshly distilled pyrrole improves repeatabilitFreshly distilled pyrrole improves repeatabilit

y.y. Due to possible instability of ppy all depositioDue to possible instability of ppy all depositio

ns and CV analysis should be done on the sns and CV analysis should be done on the same day.ame day.

CV curve performance differences difficult to CV curve performance differences difficult to illustrate due to film instability/CV variationsillustrate due to film instability/CV variations

ConclusionsConclusions

Nickel:Nickel: Something occurs during 1Something occurs during 1stst deposition that deposition that

effects subsequent Ni depositioneffects subsequent Ni deposition Possible candidates pH, release of perchlorate Possible candidates pH, release of perchlorate

anions...anions...

Shot gun approach to ideal conditions Shot gun approach to ideal conditions ineffective in this case.ineffective in this case.

Moving ForwardMoving Forward To solve the Ni deposition problem by:To solve the Ni deposition problem by:

Developing a proposal for systematic approach.Developing a proposal for systematic approach. Number of variables makes for difficult task (over 10 possibNumber of variables makes for difficult task (over 10 possib

le parameters to control)le parameters to control)

Make use of EQCM to monitor Ni depositionMake use of EQCM to monitor Ni deposition Explore parameters that haven’t been considered:Explore parameters that haven’t been considered:

PPY anionic dopant (Cl or SO4), cation-exhange membraPPY anionic dopant (Cl or SO4), cation-exhange membrane PPY(PSS), current density, NiClne PPY(PSS), current density, NiCl22, PED redux, PED redux

Perform more CV curve analysis to illustrate strPerform more CV curve analysis to illustrate structural differences in water do to current densituctural differences in water do to current density.y.

AcknowledgementsAcknowledgements

This work was supported by NSERC-USRA progThis work was supported by NSERC-USRA program and Dr. K. T. Leung’s WATLabs groupram and Dr. K. T. Leung’s WATLabs group

Presentation template and photographs courtesy Presentation template and photographs courtesy of Louis Wong.of Louis Wong.

Dr. He of CH Instruments for answering any queDr. He of CH Instruments for answering any questions I had about the electrodeposition equipmestions I had about the electrodeposition equipment in a timely fashion.nt in a timely fashion.

I would like to thank everybody in WATLabs for tI would like to thank everybody in WATLabs for there help and support.here help and support.