Development of Novel Methodologies for the Electrodeposition of Polypyrrole-based Films in Controlled Morphologies with Potential Application in Nitrate Sensing.
McCarthy, Conor P.
In this thesis the novel electrochemical deposition of poly[N-(2-cyanoethyl)pyrrole]
(PPyEtCN) into nanowire and microtube morphologies is reported. Cyclic and pulsed
electrochemical techniques were employed to electrodeposit copper micro and nano
particles at PPyEtCN and polypyrrole (PPy) surfaces. A PPy nanowire/copper
modified electrode was investigated for its effectiveness as an electrochemical sensor
for the detection of the nitrate ion.
To produce PPyEtCN in a nanowire morphology a facile, one step, electrochemical
method was employed, which did not require the use of any templates or surfactants.
Using optimised conditions the nanowires nucleated to give a homogeneous film
across the electrode surface, with lengths of approximately 2 μm and diameters of
150 nm. Evidence is presented to support an instantaneous 3-D nucleation and
growth mechanism. Structural information on the nanowires was obtained using
vibrational spectroscopy which reveals the polaron as the main charge carrier within
the polymer matrix.
To fabricate novel vertically aligned open and closed-pore microstructures of
PPyEtCN, an electrodeposition procedure was developed using an emulsion in a cosolvent
mixture. Adsorbed toluene droplets were employed as soft templates to direct
polymer growth. The microstructures only grew in the presence of both ClO4
- doping ions, due to a slower rate of polymer propagation in this electrolyte.
Two sonication methods (probe and bath) were used to form the emulsion, producing
significantly different microstructure morphologies. Control over microtube diameter
was achieved by simply altering the emulsion sonication time or the amount of
toluene added to form the emulsion. Electrochemical characterisation indicated the
PPyEtCN microtube morphology had an increased electrochemical response
compared to its bulk counterpart. TEM analysis of individual closed-pore microtubes
identified a hollow interior at the base within which the toluene droplet was
encapsulated. This cavity may be used to entrap other compounds making these
materials useful in a range of applications. The methodology was also applied to
form microstructures of poly(3,4-ethylenedioxythiophene) and PPy.
Electrodeposition of copper crystals at PPy and PPyEtCN was performed using
constant potential and cyclic voltammetry techniques. For potentiostatic deposition,
the concentration of copper and the magnitude of the overpotential were altered to
control the deposited crystal habit. Using a negative potential of -0.200 V, the
evolution of a dendrite morphology was followed using microscopy. This
morphology had an increased surface area due to the copper branching extending
into the electrolyte. PPy nanowire/copper electrodes were developed by altering the
speed and cycle number of the cyclic deposition procedure. This was an accurate
means of controlling the shape and size of the deposits. Varying the scan rate from
100 to 900 mV/s resulted in the size of the copper deposits changing from m to nm.
Sensing experiments revealed that the PPy/copper electrode was not as sensitive as a
glassy carbon/copper electrode due to interference from residual carbonate ions
remaining within the polymer matrix; however, it was observed to be more stable
over repeated cycling due to a charge transfer interaction between the copper and