Flexible/Stretchable supercapacitors have emerged as attractive prospects for
wearable and portable electronics among the next generation of energy storage
devices. These devices are resistant to shock, can be adapted to any curved surface,
and provide a less energy-consuming alternative to flexible Lithium (Li)-ion batteries.
So far, the most efficient electrodes materials for flexible/stretchable supercapacitors
have been based on carbon materials produced from fossil fuels, such as graphene,
carbon nanotubes, and conductive polymers which are expensive and limited. As a
result, there is a need for the development of cost-effective and sustainable electrode
materials for the fabrication of flexible/stretchable supercapacitors.
Biomass/plastic wastes pose a serious threat to the environment, and the massive
economy involved in the global disposal of biomass/plastic wastes has motivated us
to recycle or reuse various categories of waste in order to gain value-added carbon
products. Because of its large specific surface area, well-defined pore structure,
excellent thermal and chemical durability, intrinsic high electrical conductivity, and
wide availability, porous activated carbon (AC) is a common electroactive material for
supercapacitor applications. Over the last decade, a great deal of research has been
done on the biomass/plastic waste derived activated carbon; however, this research
has largely concentrated on the electrodes alone or coin-cell type supercapacitors,
that are unlikely to make the transfer from the laboratory to the real-world wearable
and portable electronic applications. Underpinned by a design philosophy of
sustainability and scalability, the current research aims to use a diverse range of
biomass/plastic wastes to create high surface area porous carbon materials that can
be used as electrodes in the fabrication of high energy density flexible/stretchable
supercapacitors with environmentally safe electrolytes such as bio-polymer gel and
water-in-salt electrolytes. Activated carbon derived from plant-based biomass
(hazelnut shells, corn derivatives and pomelo peel) and plastic waste (Face shield and
face mask) along with carbon composites with nanomaterials (siloxane, zinc cobalt
oxide and tin sulphide) have been explored in this thesis for application as electrode material in electrochemical supercapacitors. Physicochemical properties of the
synthesized materials were determined by X-Ray diffraction (XRD), X-ray
photoelectron spectroscopy (XPS), scanning electron microscope (SEM), transmission
electron microscope (TEM), Raman Spectroscopy and N2 adsorption/desorption
analyzer. The electrochemical performance of the as-prepared carbons was
investigated in both in three electrode system in aqueous electrolyte as well as in two
electrode system via solid state supercapacitor using biopolymer gel electrolyte.
This PhD thesis is structured into ten chapters. A short summary of those chapters is
described below.
Chapter 1-3 includes a general introduction to fundamental principles of
supercapacitors technology, biomass activated carbon and its composite electrodes,
and electrolytes for supercapacitors. Additionally, the main motivation and objectives
of this PhD Thesis are briefly presented at the end of Chapter 3.
Chapter 4 presents the synthesis of high specific surface area porous carbon from
hazelnut shells and their application in supercapacitors. By using a simple “sonoexfoliation method”, graphene like porous carbons was obtained from presynthesized activated carbon. It was observed that the textural and electrochemical
properties of the as-prepared carbon materials enhanced significantly after sonoexfoliation process. The high surface area graphene-like carbon obtained after sonoexfoliation showed excellent electrochemical performance with specific capacitance
of 320.9 F g−1 at 0.2 A g−1
current density and exceptional capacitance retention of
77.8% at 2 A g−1
current density after 10 000 cycles in 1 M Na2SO4 electrolyte.
Furthermore, the symmetric flexible supercapacitor fabricated using sono-exfoliated
graphene-like activated carbon and biopolymer gel electrolyte exhibits an outstanding
energy density of 38.7 W h kg−1 and power density of 198.4 W kg−1
.
Chapter 5 investigates the best possible precursor among different corn derivatives.
The activated carbon (AC) obtained from corn grain possessed hierarchical porous
structure with appropriate amount of N, O functional groups, high specific surface area (1804 m2 g
−1
), and a high degree of graphitization and displayed the highest
electrochemical performance among the corn derived activated carbons with a
specific capacitance (411 F g−1 at 1.0 A g−1
) and excellent rate capability (85.7%
capacitance retention at 30 A g−1
) in 6 M KOH aqueous electrolyte tested in three
electrode configuration. High specific surface area and higher degree of graphitization
are observed to play a crucial role in determining the charge accumulation properties
of activated carbon (AC) grain sample. Chapter 5 also investigated the electrochemical
behavior of flexible symmetric supercapacitor based on slot-die coated AC grain
electrodes and hydroxyethyl cellulose (HEC)/KOH bio-polymer electrolyte which
delivered an outstanding energy density of 31.1 W h kg−1 at 215 W kg−1 and ultra-high
cyclic stability (91.3% after 10000 cycles at 5 A g−1
current density).
Chapter 6 presents the synthesis of novel biomass activated carbon composite
electrodes and their applications in supercapacitors. Corn husk derived activated
carbon/two-dimensional (2D) siloxene has been utilized as a novel composite
electrode for fabricating high energy density and high temperature tolerant
supercapacitor. High surface area corn husk activated carbon was used in this study as
a suitable framework for depositing siloxene nanosheets, allowing the overall
siloxene/corn husk derived activated carbon composite to give good electrochemical
performance. The as-prepared composite electrode has a high specific capacitance of
415 F g−1 at 0.25 A g−1 and retains 73.4% of its initial capacitance even at a high current
density of 30 A g−1
in 1 M Na2SO4 electrolyte, thanks to the hierarchical porous
structure of activated carbon and sheet like siloxene structures. The siloxene
nanosheet structures act as a spacer, exposing the surface-active sites of activated
carbon for quick electrochemical reactions and ensuring maximum electrode material
utilisation. Furthermore, the symmetric supercapacitor assembled with the composite
electrodes and “acetonitrile/water-in-salt (AWIS)” electrolyte displayed best
performance with an outstanding energy density of 57.2 W h kg−1 at 338 W kg−1 with
a cyclic stability of 92.8% after 10000 cycles at 5 A g−1
current density. Besides, the
fabricated supercapacitor can operate over wide temperature range from 0 to 100 ⁰C.
| Date of Award | 7 Mar 2024 |
|---|
| Original language | English |
|---|
| Awarding Institution | - University Of Strathclyde
|
|---|
| Sponsors | University of Strathclyde |
|---|
| Supervisor | Aruna Ivaturi (Supervisor) & Leonard Berlouis (Supervisor) |
|---|