Carbon Nanofibers/ Graphene Nanoplateletes Composite as Supercapacitor Electrode Using KOH Aqueous Electrolyte

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جرار, صابرين صبري
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An-Najah National University
In this thesis, supercapacitor composite pallet electrodes had been prepared using different concentrations of carbon nanofibers and graphene nanoplateletes. The percentage weight of carbon nanofibers/ graphene nanoplateletes were changed from 90%/ 10% to 10%/ 90%, in steps of 20%. Electrochemical characterization had been characterized by cyclic voltammetry, galvanostatic charge/ discharge and electrochemical impedance spectroscopy methods in 1M KOH aqueous electrolyte. The specific capacitance was found to increase with increasing graphene nanoplateletes, which was increased from 47.0 to 119.7 F/g as graphene nanoplateletes increased from 10 to 90% weight at scan rate 5 mV/s by cyclic voltammetry method. The power and energy densities were evaluated from galvanostatic charge/ discharge method. Power and energy densities were increased with increasing graphene nanoplateletes concentration up to 70% then decreased when weight of graphene nanoplateletes increased to 90 % weight; the power density increased from 528.33 to 1095.43 W/kg, then decreased to 956.97 W/kg. The energy density increased from 2.32 to 5.26 Wh/kg, then decreased to 5.05 Wh/kg. Finally, equivalent series resistance was calculated from electrochemical impedance spectroscopy, which was found to increase with increasing graphene nanoplateletes concentrations up to 70%, then increases when graphene nanoplateletes increased to 90% weight. The equivalent series resistance was found to decrease from 1.48 to 0.632 Ω, then increases to 1.26 Ω as graphene nanoplateletes weight increases to 90%. The optimized composition in terms of best specific capacitance, power density, energy density and equivalent series resistance was 30%/ 70% of carbon nanofibers/ graphene nanoplateletes, which corresponds to 102.2 F/g, 1095.43 W/kg, 5.26 Wh/kg and 0.632 Ω, respectively. The specific surface area, pore size distribution and morphology structure of the prepared composites had been investigated by Brunauer- Emmett- Teller, Barrett- Joyner- Halenda, Harkins- Jura methods and scanning electron microscope. It is found that the specific surface area increases with increasing graphene nanoplateletes concentrations. It was increased from 271.27 to 665.93 m^2/g as graphene nanoplateletes changed from 10% to 90% weight. Total pore volume increases with increasing graphene nanoplateletes weight up to 70%, then it decreases as the concentration of graphene nanoplateletes increases to 90%. The total pore volume increased from 1.22 to 1.72 cm^3/g, then it decreased to 1.33 cm^3/g. Furthermore, micro, ultra- micro and mesopore volumes were found to increase by increasing graphene nanoplateletes concentrations from 10 to 90%. Micropore volume increases from 0.023 to 0.08 cm^3/g, ultra- micropore volume increases from 0.023 to 0.28 cm^3/g and mesopore volume increases from 0.55 to 0.88 cm^3/g when graphene nanoplateletes increase from 10% to 90% weight, respectively. Finally, Macropore volume increases with increasing graphene nanoplateletes from 10% to 30%, which decreases from 0.64 to 0.29 cm^3/g, and then increases up to 70% weight of graphene nanoplateletes, which increases from 0.29 to 0.88 cm^3/g, then it decreases for graphene nanoplateletes 90% weight; 0.33 cm^3/g. The best structural characterization was found for 70% weight of graphene nanoplateletes, which has the highest total pore volume (1.72 cm^3/g) and the highest macropore volume (0.88 cm^3/g). Also, it has optimized higher specific surface area, micropore, ultra- micropore and mesopore volumes which was 528.52 m^2/g, 0.0614 cm^3/g, 0.234 cm^3/g and 0.78 cm^3/g, respectively.