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

One of the technical advances made by the lead-acid battery industry in the field of portable power supply was the development of the valve regulated lead-acid battery (VRLA). This battery reduced the necessity for periodic servicing in terms of having to replenish the cells with distilled water. Further, this new type of battery can now be installed near sensitive electronic equipment without the danger of acid spill or dangerous fumes being emitted. In addition, longer service performance is achieved in terms of life cycle capacity, when compared to the conventional flooded type batteries. However, the new type of battery requires the manufacturing of high precision electrodes and components with low tolerances for error. In order for the manufacturers to produce such a premium product, a thorough understanding of the electrochemistry of the inner components is necessary. None of the South African lead-acid battery manufacturers are currently making VRLA batteries to supply a very competitive global market, where a large range of sizes and capabilities are available. In order to introduce the VRLA battery into such a competing market in South Africa, a niche area for its application was identified in order to establish the viability of manufacturing such a battery locally. This is done by integrating the VRLA concept into an existing battery, such as the miners cap lamp (MCL) battery. Its application is specific with well-defined performance criteria in a relatively large consumable market in the South African mining industry. The study looked at various components within a local manufacturing environment that required a better understanding and modification of the processes to build VRLA MCL batteries. This included a detailed study of the manufacturing processes of the positive electrode. The study involved the investigation of the types of grid alloys used, the type of electrode design, such as tubular or flat plate, the addition of redlead to the paste mixing process and subjecting the batteries to accelerated life cycle testing. A better understanding of the oxygen recombination cycle was also performed in order to evaluate the correct use of certain design criteria in the manufacturing process. This included the study of the pressure release valve and the type of positive electrode used. The study also looked at developing an inexpensive analytical technique to evaluate the porosity of cured and formed electrodes using a glycerol displacement method. The monitoring of the state of health (SoH) of VRLA batteries on a continuous basis is an important parameter in unique applications such as remote power supply. A device was developed to monitor the SoH of VRLA batteries on a continuous basis. The working principle of the device was tested on a MCL VRLA battery. With the development of other types of VRLA batteries for specific applications such as in stand-by power supplies, the monitoring device would then be integrated in the battery design.