Fabrication and characterization of nickel-coated polyethylene terephthalate supported mangabese dioxide thin-film electrochimical capacitor prototypes
Energy deficiency has always been a pressing global concern especially during the midst of the ditch of the world's oil reserve meagrely supplying 80% to 90% of the current worldwide energy consumption. The increasing demand of fossil fuels at the turn of the millennium can be incontrovertib...
Saved in:
| Main Author: | |
|---|---|
| Format: | Thesis |
| Language: | English |
| Published: |
2011
|
| Subjects: | |
| Online Access: | http://ir.unimas.my/id/eprint/13761/2/Boon%20%28fulltext%29.pdf |
| Tags: |
Add Tag
No Tags, Be the first to tag this record!
|
| Summary: | Energy deficiency has always been a pressing global concern especially during the midst
of the ditch of the world's oil reserve meagrely supplying 80% to 90% of the current worldwide
energy consumption. The increasing demand of fossil fuels at the turn of the millennium can be
incontrovertibly associated with the exponential growth of human population resulted in the
worrying surge of oil's price where in search of replacement for this finite resources is direly
needed. In today's society, dramatic advancement in modern electrical technologies which we
are heavily dependent on has altered the globe's energy requirement to cheaper, cleaner, durable,
efficient and sustainable energy resources. In respond to the paradigm-shift, concerted efforts are
being focused on the development of high performance energy-storage systems that are capable
of meeting the ever increasing energy demand of various device applications., As such, our
present study entails the fabrication of manganese dioxide (Mn02) thin film electrochemical
capacitor prototypes via novel prototyping process (Patent Pending PI 20094040) of core interest
focused predominantly on utilizing ubiquitous and environmentally benign materials, optimizing
electrode configuration and nanostructuring of electroactive material (Mn02).
Of all electroactive materials, manganese dioxide is specially selected as it not only
fulfills the basic criteria for electrode materials as being cheap and toxicologically harmless, but
also exhibits superior capacitive behaviour comparable to that of ruthenium dioxide. Ruthenium
dioxide despite being regarded as the quintessential electrode material to date, its potential
applications are commercially unviable where the limiting factor mainly lies in the expensive
cost of production. The rapid prototyping process which we have developed entails the
deposition of manganese dioxide thin films on metallized poly(ethylene terephthalate) substrate using the novel horizontal submersion approach. Interdigitated array (IDA) electrodes of
different configurations were generated using a computer interfaced cutting plotter. Subsequently
a conformal agar-based gel electrolyte layer containing dissolved Na2SO4 salt was deposited by
solution casting directly onto the IDA electrodes. These prototypes of different IDA electrode
configurations were studied using various established characterization techniques. Both
electrochemical and material characterizations of the thin-film Mn02 electrochemical capacitor
prototypes showed promising electrochemical properties with excellent capacitive performance
and cycling reversibility. Morphological characterizations showed that the deposited manganese
dioxide thin films were largely nanoparticulate in nature and possess high electrochemically
active surface area. Noticeable morphological changes of Mn02 film were observed during
voltammetric cycling in which the film was slowly transformed into a well-organized and
interconnected petal-like microstructure. As a result, Mn02 electrodes of enhanced cycling
stability and capacitive behaviour were obtained. However, the physicochemical mechanisms
that governed the observed morphological changes which led to the formation of foregoing
microstructure remained unclear. Much research on the synthesis of nanomaterials is
imperatively necessary to better understand the myriad of fundamental interactions at nanoscale
level. Electrodes of desired microstructures can therefore be finely architectured to obtain
enhanced capacitive performance.
Cyclic voltammetry studies on Mn02-based electrochemical capacitors with dual planar
IDA electrode configurations showed that the capacitive performance is more superior compared
with ECs of conventional parallel electrode configuration in terms of the specific capacitance,
cycling stability and coulombic efficiency. Electrochemical impedance spectroscopy provides
complimentary data to that obtained by cyclic voltammetry. The impedance characteristics of Mn02-based electrode were measured at predetermined frequency range and amplitude of
alternating/direct current potential. A Nyquist plot of Mn02-based electrochemical capacitors
with IDA electrode configurations indicated distinctive impedance responses which include: 1) a
nearly pure capacitive behaviour represented by vertical plot of phase angle approximate to
at low frequencies, 2) a diffusion controlled behaviour represented by inclined plot of phase
angle approximate to it/4 at intermediate frequencies, and 3) a purely resistive behaviour
represented by depressed semicircular arc at high frequencies. The exceptional capacitive
performance of EC prototypes of IDA electrode configuration could be attributed to the
enhanced ionic conductivity associated with the shorter ionic diffusion path length and
utilization of electroactive materials. The major advantage of IDA electrode configuration is that
each pair of electrode array can be potentiostated individually and hence resulted in a higher
reaction kinetic by providing a shorter diffusion path length between adjacent electrodes for
redox electroactive species.
Despite its long-standing merits as the cathode electrode of commercial batteries, the
Mn02-based electrode is currently being extensively studied for electrochemical capacitor
applications. The functionalities of Mn02-based electrodes have inspired an attempt to
fabricate novel hybrid energy storage prototype which comprises a battery and an
electrochemical capacitor being integrated as a single embodiment. It is denoted as the Hybrid
Batt-EC prototype which consists of two Mn02-based EC prototypes with IDA electrode
configuration 2, and a piece of galvanized zinc inserted between these IDA EC prototypes.
Chronopotentiometry evaluation of this hybrid device showed encouraging results with energy
density of 1.17 x 10-3 Ah or 1.17 mAh could be obtained at a discharge current of 0.01 mA. It is envisaged that nanostructuring of electroactive materials offers a more accurate
and precise control on the microstructures and porosity (uniform distribution of pores) of
desirable electrochemical characteristic. It is recommended that future works should address
the effect of microstructural parameters, namely film thickness and homogeneity, grain size,
porosity and electrochemically active surface area, and optimized interdigitated array (IDA)
electrode configurations. |
|---|