Thesis (M.Sc. (Chemistry)) -- University of Limpopo, 2021 / Recently, the use of electrochemical supercapacitors as energy storage devices has
drawn great attention due to their high charge/discharge rate, long life span, high
power and energy densities. However, the choice of electrode materials used is vital
for the performance of supercapacitors. This study focused on the development of a
low cost hybrid electrode based on reduced graphene oxide/metal organic framework
composite (rGO/MOF) and a novel palladium (Pd) nanoparticles loaded on rGO/MOF
termed Pd-rGO/MOF nanocomposite. The prepared nanocomposites were used for
high performance electrochemical double layer capacitor-(EDLC) and battery-type
supercapacitors known as supercabattery.
The rGO material reported in this work was chemically derived through the oxidation reduction method using a hydrazine as a reducing agent. Furthermore, palladium
nanoparticles were loaded on the rGO using the electroless plating method. The
rGO/MOF and novel Pd-rGO/MOF nanocomposites were prepared using an
impregnation method in dimethylformamide. The physical and morphological
properties of the synthesised materials were investigated using scanning electron
microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD),
Fourier transform infrared spectroscopy (FTIR), energy dispersive X-ray spectroscopy
(EDX), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA).
The XRD and FTIR analyses showed crystalline phases and vibrational bands for both
parent materials, respectively. The TGA/DSC results showed enhancement of the
thermal stability of the composite as compared to MOF material. The SEM/EDS and
TEM/EDX confirmed the presence of octahedral structure of MOF in the rGO sheet like structure and elemental composition of the synthesised composite. The resultant
of Pd-rGO/MOF nanocomposite showed a morphology in which a thin layer of rGO
coating existed over MOF with unique bright spots indicating the presence of Pd
nanoparticles. This observation agreed well with the structural properties revealed by
both XRD and FTIR with the reduction of MOF intensities upon Pd-rGO loading as well
as enhancement of thermal stability of the nanocomposites. The electrochemical
properties of the prepared electrodes were determined using cyclic voltammetry (CV),
galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy
(EIS). To evaluate the electrochemical performance of the prepared electrode
materials, both two and three electrode cells were assembled. From the CV and GCD
results, the nanocomposites demonstrated a battery-type behaviour and therefore
asymmetric supercabattery cells were assembled using the composites as positive
electrodes, and activated carbon as a negative electrode. The specific capacity of
rGO/MOF in three electrode cell was found to be 459.0 C/g at a current density of 1.5
A/g in 3M potassium hydroxide. Furthermore, the asymmetric supercapacitor based
on the rGO/MOF nanocomposite and activated carbon (AC) as a negative electrode
exhibited a maximum energy density of 11.0 Wh/kg and the maximum power density
of 640.45 W/kg. The loading of palladium nanoparticles on the nanocomposite was to
improve the electrochemical active sites and the performance of the supercapacitor
electrode. After incorporation of Pd nanoparticles, the specific capacitance in three
electrode cell improved to 712 C/g at a higher current density of 2 A/g with the same
electrolyte. The assembled supercabattery has shown improved maximum energy and
energy density of 26.44 Wh/kg and 1599.99 W/kg, respectively. Based on these
findings, the synthesised rGO/MOF and Pd-rGO/MOF nanocomposites are promising
electrode materials for future supercabattery applications. / NRF (National Research Foundation) and
SASOL foundation
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ul/oai:ulspace.ul.ac.za:10386/3674 |
| Date | January 2021 |
| Creators | Teffu, Daniel Malesela |
| Contributors | Modibane, K. D., Hato, M. J., Makgopa, K. |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | 139 leaves |
| Relation |
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