الفهرس 
Chapter 1 IntroductionOnly 14 pages are availabe for public view
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Abstract
Energy storage systems controlled by current fast power electronic converters may play a crucial part in meeting the worldwide energy savings problem. Supercapacitors have garnered a great deal of attention due to their high energy density, extended lifespan, quick charge/discharge rate, and environmentally friendly nature. Electrode materials play a crucial impact on supercapacitors’ final performance.
The present work concerns the preparation of nanostructured materials as supercapacitor electrodes. The first part reports the study of synthesized graphene materials by different preparation methods and their effect on the physicochemical and electrochemical behavior of graphene. The evaluation of graphene materials as supercapacitors via the three-electrode system was performed, and the results show that the best performance (highest capacitance of 696 F/cm3 at a current density of 0.6 A/g, and excellent stability of 103% capacitance retention after 9000 cycles) was for the sample prepared by the electrochemical exfoliation method. The symmetric supercapacitor device assembled for the best sample (GE) achieved a volumetric capacitance of 204.5 F/cm3 at a current density of 0.3 A/g with a high energy density of 16.3 Wh/kg and high stability; retaining " ~ "89% of the original specific capacitance after 3000 charge-discharge cycles.
The second part deals with the green synthesis of MnO2 and its nanocomposites with graphene. The electrochemical behavior was studied and the findings reveal that the nanocomposite sample GMW has the highest performance; specific capacitance of 500 F/g at 1 A/g and stability of 71% after 7000 cycles. Furthermore, an asymmetric supercapacitor device was combined using the GMW and GE samples as the positive and negative electrodes, respectively. The asymmetric system has a specific capacitance of 167 F/g at 0.5 A/g, stability of 94% after 2000 cycles, and energy density of 18.9 Wh/kg.
In the last part of the study, the pure spinel phase of NiCo2O4 was successfully prepared by electrodeposition at different times (5, 10, 20, and 30 minutes) using a fixed voltage of 2 V followed by thermal annealing at 300 °C. By increasing the electrodeposition time, interconnected nanosheets of oxide layers are deposited and agglomerated above each other leading to block the pores or the active sites responsible for the ion’s transportation. Graphene was added to the optimum deposition time of 5 min to prepare NiCo2O4/GE composite, in order to study the effect of graphene presence. The electrochemical behavior via the three-electrode system revealed that the sample NiCo2O4-5 has the best performance; specific capacitance of 1183 F/g at 0.5 A/g, extraordinary stability of 127% after 10000 cycles, and high conductivity of 3.14 Ω. While in the presence of graphene the capacitance was 958 F/g and the stability retention was 93% after 10000 cycles. The NiCo2O4-5 sample was used as positive and negative electrodes to produce a symmetric supercapacitor. The specific capacitance was 150 F/g at 5 A/g, stability retention was 105% after 5500 cycles, and the energy density was 7.5 Wh/kg.