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Abstract

Carbon, one of the most abundant materials in the earth crust, has gained research
attention owing to its high structural stability, electrical conductivity, optical and thermal
properties. Additionally, the possibility of tailoring carbon materials at nanoscales makes
them promising materials for many applications, including energy storage, sensors, biomedical
and electronics. One of the highest potential applications of carbon-based
nanomaterials are energy storage devices to store energy considering the increasing demand
for alternative energy resources for fulfilling consumer needs. Therefore, enormous efforts
were already employed to design advanced carbon materials for energy storage by
nanostructure design, surface engineering and nanocomposite formation. However, most
commonly used synthesis and processing techniques are limited due to the high energy and
high-temperature requirements for the fabrication, large time consumption, and
uncontrollability of the nanoengineering. Thus, developing a new technique for the
controllable nanoengineering of advanced carbon materials at a large scale that is more
efficient is necessary for application-oriented purposes.
In this PhD dissertation, plasma-enabled techniques are used for developing advanced
carbon-based electrodes for energy applications. In order to attain the research objectives,
the PhD research has been designed into three stages: (i) developing plasma techniques for
fabricating carbon nanostructures, (ii) designing hybrid carbon-based electrodes, and (iii)
exploring energy storage performances of the designed electrodes. A cold low-pressure
plasma is explored in the first stage as a promising approach for designing advanced carbon
materials at the nanoscale. We tested different plasma systems for the synthesis of carbon
nanostructures. In all cases, a radio-frequency power generator was used for plasma
discharge. The first approach was the deposition of carbon nanostructures from vapour
phase to the solid phase using carbon-containing gases in plasma as the precursors. In the
second approach, we have established an alternative technique by growing carbon
nanostructures by the surface reformation of a solid precursor using an argon/ hydrogen
gas mixture. In both cases, we investigated the influence of plasma discharge parameters
on the nanostructures growth mechanisms.
In the second stage of this PhD research, we demonstrated the ability of plasma for
surface engineering and heteroatom doping in both low-pressure and atmospheric
conditions. In the former, carbon nanostructures were exposed to nitrogen-containing lowpressure
plasmas for fabricating the nitrogen-doped carbon nanowalls. Furthermore, in the
latter, at atmospheric conditions, entangled carbon nanotubes were treated with a plasma
jet of inert gas. We revealed the surface engineering mechanisms in both cases and
determined the changes in the surface properties.
In the final stage, we designed hybrid carbon-based nanostructures for energy storage
applications. We have chosen the plasma-enabled techniques that were used in the first
and second stages of our investigation for designing carbon nanostructure platforms and,
in addition, a thermal annealing technique for designing carbon/metal sulphide hybrid
composite. Afterwards, we have studied the electrochemical properties of the fabricated
electrodes for batteries and supercapacitors and demonstrated that the fabricated
electrodes were delivering one of the best performances among similar carbon-based
materials.
The presented PhD dissertation offers insight into the superiority of plasma-enabled
techniques for designing hybrid carbon-based electrodes. In addition, the method offers a
2-in-1 package, as one can also tailor the properties of the synthesised electrodes either
during the synthesis process or afterwards. Examples of using such plasma techniques have
been demonstrated in the thesis for the preparation of electrodes that have superior
properties when used as electrodes for lithium-ion batteries or supercapacitors.