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

1
Influence of Current Density on Polypyrrole (PPY)
Properties and Approaching the Electrochemical
Deposition of Nickel Nanoparticles on PPY
Ni deposited on ppy (20s at 1.2mA) using
Amperometric i-t E-1.25V, Q1.92mC t17.5s
Prepared By Mark Pynenburg NSERC-USRA WA
TLabs, University Of Waterloo
Cu deposited on ppy (1600s at 15uA) using
Amperometric i-t E-1.2V, Q0.5635mC t1.3s
2
Outline

• Experimental Objectives.
• Experimental Setup.
• Wafer Preparation
• Electrochemical Deposition Station.
• SEM/AFM Imaging
• Current Density.
• Motivation
• Theoretical
• Discussion
• Nickel Deposition.
• Pulse Electrodeposition (PED)
• 2nd Deposition Problem
• Conclusions
• Moving Forward
• Acknowledgements

3
Experiment Objectives

• To explore the effects of current density on ppy
  film properties.
• To prepare monoshaped and monosized nickel
  nanoparticles on ppy film by electrochemical
  deposition.

4
Experimental Setup

• Preparation of Au sputtered 2.5mm X 15mm Si
  Wafer
• Ultrasonic pre-cut wafers in wash acetone.
• Rinse wafers with isopropyl alcohol.
• Bake wafers _at_ 80C under vacuum. Purging once with
  nitrogen after ½ hour then under vacuum again for
  1 hour.
• 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.
• Use electrochemical station (potentio/galvanostat)
  to deposit ppy and metals.

5
Electrochemical Station
Working Electrode
Stored in 3M KCl Solution
Counter Electrode
Reference Electrode
Au covered Si wafer
V
A
Computer Display Output
Electrochemical Control Module
6
Electrochemical 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
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Scanning Electron Microscopy
8
Atomic Force Microscopy
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Current Density

• Motivation
• 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 Conclusions
• Current density crucial parameter in determining
  properties of ppy.
• Low current density closer to intrinsic
  properties of pure ppy. Should be used as a
  reference for investigating effects of changing
  conditions on properties.
• Adding water has little or no influence on
  properties of this modification but lowers
  stability.
• Lower current density incorporates more anions.

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Theoretical

• Pyrrole dissolved in solvent with anionic doping
  salt is oxidized at the surface of an electrode
  by application of an anodic potential.
• As s result of initial oxidation, the radical
  cation formed reacts with other monomers to form
  oligomeric products and then the polymer.
• Conjugation in the polymer lowers its oxidation
  potential wrt to monomer. Therefore synthesis and
  anionic doping occur concurrently.
• Anion is incorporated into polymer to ensure
  electrical neutrality of film.
• Mechanism is controversial - of competing
  schemes
• Equation governing thickness of ppy deposition

Q i x t A .15 to .1875 cm2 Mppy
67.09 g/mol F 96500C/mol n (2 .025) p
density (0.967,1.2, 1.5g/cm3?)
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PPY Density Determination Using Quasiempirical
Method
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PPY Density Determination Using Quasiempirical
Method

• 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 ? 2.9 to 1.6g/cm3
• Lower number seems more reasonable. Agrees
  better with literature and previous value.
• Formula doesnt account for the doping anions.
• Instead of talking about ppy thickness use
  galvanostatic current and time of polymerization.

13
Discussion

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

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Variations in PPY due to age of pyrrole

• Larger variation in ppy depositions before
  freshly distilling pyrrole
• Top old ppy 1600s 15uA dep potential varies by
  0.07V
• Bottom fresh ppy 2000s 12uA dep potential varies
  by 0.014V

15
The effect of PPY age on Cu deposition
Cu deposited on ppy using Amperometric i-t E
-1.4V, Q0.5635mC, t lt 1s Top left ppy 20s/1.2mA,
Top right 160s/150uA, left 1000s/24uA Red day
old ppy film Blue fresh ppy film
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Current Density on Cu Deposition

• Red 20s 1.2mA
• Blue 160s 0.15mA
• Brown 500s 48uA
• Green 1000s 24uA
• Navy 2000s 12uA

Cu deposited on ppy using Amperometric i-t
E-1.4V, Q0.5635mC t lt1s
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Current Density on Cu Deposition -1.2V Deposition
time varied with film type/age
ppy 320s _at_ 75uA
ppy 160s _at_ 150uA
ppy 800s _at_ 30uA
ppy 1600s _at_ 15uA
18
The trouble with cyclic voltammograms (CVs)

• Six identically deposited ppy films gave vastly
  different results when CVs done in dep.
  electrolyte 0.1M NaClO4

19
Nickel

• Observed similar results to earlier work of Neha
  and Sabrina
• Both observed ppy 2 step due likely to monomer
  age which may have effected Ni deposition
  properties
• When Ni deposition has occurred usually very low
  numbers
• Varying pH and potential yielded little new
  information

20
Nickel

• When ppy is reduced the incorporated perchlorate
  anions are released according to the reaction
• (PPyClO4-) e- ? PPy0 ClO4-
• Metals are to be deposited by reduction.
• Reduction current has two components, one due to
  reduction of ppy with simultaneous release of
  anions as counterions illustrated above, and when
  a negative enough potential for Ni reduction is
  applied
• NiSO42 2e ? Ni0 xSO4

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Nickel

• However picture is much more complicated
• Boric Acid is used as a buffer at electrode
  surface.
• Sulfuric acid is used to acidify medium to
  supress formation of hydroxides.
• Deposited Ni can act as a catalyst for hydrogen
  evolution, different sites on Ni deposit can
  favour a variety of adsorbants, mechanism of
  deposition complicated.
• See papers Nanocrystalline Copper by Pulsed
  Electrodeposition, H. Natter R. Hempelmann, J.
  Phys. Chem. 1996, 100, 19525-19532. and First
  Stages of Ni Deposition on Vitreous Carbon from
  Sulfate Solutions, A. G. Munoz et al., Thin
  Solid Films, 429 (2003) 119-128.

22
Nickel
23
Nickel
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Pulse Electrodeposition (PED)

• Motivation
• Nanocrystalline Copper by Pulsed
  Electrodeposition, H. Natter R. Hempelmann, J.
  Phys. Chem. 1996, 100, 19525-19532.
• Use shape of current pulses to influence grain
  size, distribution, shape.
• Truncated octahedral Cu formed exhibiting self
  organizational behaviour
• Initial Ni experiments using PED not as
  promising.

25
Pulse Electrodeposition (PED)

• Short (1 to 10ms) high current/potential pulse
  followed by long rest (gt100ms)
• High nucleation rate
• Surface of electrode has chance to return to
  equilibrium
• Nature of diffusion controlled growth changed

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Ni vs. Cu 2nd Deposition

• Ni deposition exhibits behavior not observed in
  Cu deposits.
• Often only the first deposition leads to and

Cu close agreement between 1st 2nd dep.
1st Ni dep.
2nd Ni dep.
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Conclusions

• Current density
• Has an effect on the nature of ppy film as
  illustrated by Cu deposition.
• Could be due to better ppy conductivity, greater
  incorporation of anion
• Freshly distilled pyrrole improves repeatability.
• Due to possible instability of ppy all
  depositions and CV analysis should be done on the
  same day.
• CV curve performance differences difficult to
  illustrate due to film instability/CV variations

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Conclusions

• Nickel
• Something occurs during 1st deposition that
  effects subsequent Ni deposition
• Possible candidates pH, release of perchlorate
  anions...
• Shot gun approach to ideal conditions ineffective
  in this case.

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Moving Forward

• To solve the Ni deposition problem by
• Developing a proposal for systematic approach.
• Number of variables makes for difficult task
  (over 10 possible parameters to control)
• Make use of EQCM to monitor Ni deposition
• Explore parameters that havent been considered
• PPY anionic dopant (Cl or SO4), cation-exhange
  membrane PPY(PSS), current density, NiCl2, PED
  redux
• Perform more CV curve analysis to illustrate
  structural differences in water do to current
  density.

30
Acknowledgements

• This work was supported by NSERC-USRA program and
  Dr. K. T. Leungs WATLabs group
• Presentation template and photographs courtesy of
  Louis Wong.
• Dr. He of CH Instruments for answering any
  questions I had about the electrodeposition
  equipment in a timely fashion.
• I would like to thank everybody in WATLabs for
  there help and support.