Browsing by Author "Ndipingwi, Miranda M."
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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 Microscopic, spectroscopic, and electrochemical characterization of novel semicrystalline poly(3-hexylthiophene)-based dendritic star copolymer(MDPI, 2022) Yonkeu, Anne L. Djoumessi; Ndipingwi, Miranda M.; Tovide, Oluwakemi O.: In this study, electron-donating semicrystalline generation 1 poly(propylene thiophenoimine)- co-poly(3-hexylthiophene) star copolymer, G1PPT-co-P3HT was chemically prepared for the first time. Copolymerization was achieved with high molecular weight via facile green oxidative reaction. 1H NMR analyses of the star copolymer demonstrated the presence of 84% regioregular (rr) head-to-tail (HT) P3HT, which accounts for the molecular ordering in some grain regions in the macromolecule’s morphology, as revealed by the high-resolution scanning electron microscopy (HRSEM) and Selected Area Electron Diffraction (SAED) images, and X-ray diffraction spectroscopy (XRD) measurements. The star copolymer also exhibited good absorption properties in the ultraviolet-visible (UV-Vis) and the near infrared (NIR) spectral regions, which give rise to an optical energy bandgap value as low as 1.43 eV. A HOMO energy level at −5.53 eV, which is below the air-oxidation threshold, was obtained by cyclic voltammetry (CV). Electrochemical impedance spectroscopy (EIS) ascertained the semiconducting properties of the macromolecule, which is characterized by a charge transfer resistance, Rct, value of 3.57 kΩ and a Bode plot-phase angle value of 75◦ .Item Microscopic, spectroscopic, and electrochemical characterization of novel semicrystalline poly(3-hexylthiophene)-based dendritic star copolymer(MDPI, 2022) Djoumessi Yonkeu, Anne L.; Ndipingwi, Miranda M.; Tovide, Oluwakemi O.In this study, electron-donating semicrystalline generation 1 poly(propylene thiophenoimine)- co-poly(3-hexylthiophene) star copolymer, G1PPT-co-P3HT was chemically prepared for the first time. Copolymerization was achieved with high molecular weight via facile green oxidative reaction. 1H NMR analyses of the star copolymer demonstrated the presence of 84% regioregular (rr) head-to-tail (HT) P3HT, which accounts for the molecular ordering in some grain regions in the macromolecule’s morphology, as revealed by the high-resolution scanning electron microscopy (HRSEM) and Selected Area Electron Diffraction (SAED) images, and X-ray diffraction spectroscopy (XRD) measurements. The star copolymer also exhibited good absorption properties in the ultraviolet-visible (UV-Vis) and the near infrared (NIR) spectral regions, which give rise to an optical energy bandgap value as low as 1.43 eV. A HOMO energy level at 5.53 eV, which is below the air-oxidation threshold, was obtained by cyclic voltammetry (CV).Item Pseudocapacitive effects of multi-walled carbon nanotubes-functionalised spinel copper manganese oxide(MDPI, 2022) Nolly, Christopher; Ikpo, Chinwe O.; Ndipingwi, Miranda M.Spinel copper manganese oxide nanoparticles combined with acid-treated multi-walled carbon nanotubes (CuMn2O4/MWCNTs) were used in the development of electrodes for pseudocapacitor applications. The CuMn2O4/MWCNTs preparation involved initial synthesis of Mn3O4 and CuMn2O4 precursors followed by an energy efficient reflux growthmethod for the CuMn2O4/MWCNTs. The CuMn2O4/MWCNTs in a three-electrode cell assembly and in 3 M LiOH aqueous electrolyte exhibited a specific capacitance of 1652.91 F g1 at 0.5 A g1 current load. Similar investigation in 3 M KOH aqueous electrolyte delivered a specific capacitance of 653.41 F g1 at 0.5 A g1 current load. Stability studies showed that after 6000 cycles, the CuMn2O4/MWCNTs electrode exhibited a higher capacitance retention (88%) in LiOH than in KOH (64%).