Browsing by Author "Dywili, Nomxolisi"
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Item High power asymmetric supercapacitor based on activated carbon/reduced graphene oxide electrode system(Elsevier, 2023-02-22) Dywili, Nomxolisi; Ntziouni, Afroditi; Ndipingwi, Miranda M.; Ikpo, Chinwe; Nwanya, Assumpta C.; Kordatos, Konstantinos; Iwuoha, EmmanuelWe synthesized Graphene oxide (GO) using the modified Hummers method and further reduced to reduced graphene oxide (rGO) using hydrazine monohydrate and ammonia solution. The prepared materials were interrogated using different characterization techniques to determine which of them is more suitable for supercapacitor application. High resolution scanning electron microscopy (HRSEM) revealed a sheet-like morphology of separated thin sheets and wrinkled edges for GO, whereas rGO consist of thinner sheets with smaller pores than GO. The structural studies as elucidated from X-ray diffraction (XRD) shows that the GO has more interlayer spacing due to a higher oxygen content as compared to the rGO. The oxygen containing functional groups seen in GO either disappear or are greatly reduced in intensity in rGO as evidenced from the Fourier transform infrared spectroscopy (FTIR) of the materials. The electrochemical studies indicate that the rGO gave a higher current response compared to GO and a specific capacitance of 105.3 and 56.7 F g 1 respectively was delivered by rGO and GO at a scan rate of 10 mV s 1 in a three-electrode set-up. Asymmetric supercapacitor cells using GO and rGO as positive electrodes and activated carbon as the negative electrodes gave the highest specific capacitance value of 94.3 F g 1 for the AC//rGO cell and 59.6 F g 1 for the AC//GO cell at a current load of 0.25 A g 1. The specific capacitance obtained from the AC//rGO is comparable to most recorded values for rGO electrodes. A high specific power of 6411.7 W kg 1 was obtained at a specific energy of 22.6 W h kg 1 while at a specific energy of 25.7 W h kg 1, a specific power of 700.1 W kg 1 was obtained for the AC//rGO. This is due to the more porous and thinner sheet of the rGO. The overall results showed that the rGO gave better supercapacitive properties than the GO.Item High power asymmetric supercapacitor based on activated carbon/reduced graphene oxide electrode system.(2023-01) Dywili, Nomxolisi; Ndipingwi, Miranda M.; Ikpo, Chinwe; Nwanya, Assumpta C.; Iwuoha, Emmanuel; Ntziouni, Afroditi; Kordatos, KonstantinosWe synthesized Graphene oxide (GO) using the modified Hummers method and further reduced to reduced graphene oxide (rGO) using hydrazine monohydrate and ammonia solution. The prepared materials were interrogated using different characterization techniques to determine which of them is more suitable for supercapacitor application. High resolution scanning electron microscopy (HRSEM) revealed a sheet-like morphology of separated thin sheets and wrinkled edges for GO, whereas rGO consist of thinner sheets with smaller pores than GO. The structural studies as elucidated from X-ray diffraction (XRD) shows that the GO has more interlayer spacing due to a higher oxygen content as compared to the rGO. The oxygen containing functional groups seen in GO either disappear or are greatly reduced in intensity in rGO as evidenced from the Fourier transform infrared spectroscopy (FTIR) of the materials. The electrochemical studies indicate that the rGO gave a higher current response compared to GO and a specific capacitance of 105.3 and 56.7 F g−1 respectively was delivered by rGO and GO at a scan rate of 10 mV s−1 in a three-electrode set-up. Asymmetric supercapacitor cells using GO and rGO as positive electrodes and activated carbon as the negative electrodes gave the highest specific capacitance value of 94.3 F g−1 for the AC//rGO cell and 59.6 F g−1 for the AC//GO cell at a current load of 0.25 A g−1. The specific capacitance obtained from the AC//rGO is comparable to most recorded values for rGO electrodes. A high specific power of 6411.7 W kg−1 was obtained at a specific energy of 22.6 W h kg−1 while at a specific energy of 25.7 W h kg−1, a specific power of 700.1 W kg−1 was obtained for the AC//rGO. This is due to the more porous and thinner sheet of the rGO. The overall results showed that the rGO gave better supercapacitive properties than the GO.Item Polyanilino-graphene oxide intercalated with platinum group metal nanocomposites, for application as novel supercapacitor materials(University of the Western Cape, 2014) Dywili, Nomxolisi; Iwuoha, Emmanuel I.Supercapacitors are one of the important subjects concerning energy storage which has proven to be a challenge in this country. Currently, the electrodes of most commercial supercapacitor are made of carbon which is known to be inexpensive and has high resistance to corrosion. These carbon based supercapacitors operate under EDLC. They offer fast charging/discharging rates and have the ability to sustain millions of cycles without degrading. With their high power densities, they bridge the gap between batteries which offer high energy densities but are slow in charging/discharging and conventional dielectric capacitors which are very fast but having very low energy densities. The objective of this work was to develop a high performance supercapacitor using polyanilino-graphene oxide intercalated with platinum group metal nanocomposites. Specific capacitance of each material was investigated with the objective of ascertaining the material that has the best capacitance. In this work, GO was functionalized with aniline and intercalated with Pt, Pd and Pd-Pt nanocomposites. The nanomaterials were characterized with FTIR, Ultravioletvisible (UV-visible) spectroscopy, high resolution scanning electron microscopy (HRSEM), high resolution transmission electron microscopy (HRTEM), energy dispersive x-ray microanalysis (EDS) and X-ray diffraction (XRD) analysis. The composites were tested for possible application as supercapacitor materials using potentiostatic-galvanostatic constant current charge/discharge. The synthesized materials had good electronic, mechanical, optical, physical etc. properties as proven by the various characterization techniques but they proved not to be ideal for application as supercapacitor materials. The materials tested negative when tested for both anodic and cathodic materials therefore we can conclude that the materials are not good supercapacitor materials and therefore cannot be used in application as novel as supercapacitors.