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Design and Fabrication of Supercapacitors based on Doped Carbon Nanostructure Composites and Redox Electrolytes

Abbasi, Samaneh | 2025

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 58349 (03)
  4. University: Sharif University of Technology
  5. Department: Chemistry
  6. Advisor(s): Shahrokhian, Saeed
  7. Abstract:
  8. The low energy density of supercapacitors primary limiting their widespread practical applications. Redox electrolytes have recently emerged as an effective strategy for simultaneously boosting both the energy and power density of supercapacitors. In the first research, carbon spheres were prepared using an environmentally friendly hydrothermal carbonization method. These carbon spheres were then coated with zinc and iron chloride salts. Following a high-temperature thermal treatment, a carbon structure with a high surface area and an efficient porous structure was obtained. Subsequently, various heteroatoms, including nitrogen, boron, phosphorus, and sulfur, were introduced into the porous carbon structure to enhance their wettability and electrochemical active surface area. Ultimately, based on the experimental findings, NPCSs and BPCSs coated on graphene sheets were utilized as the positive and negative electrodes in the construction of an asymmetric supercapacitor. Furthermore, a mixture of anthraquinone sulfonic acid (AQSA) and potassium iodide (KI) was employed as a dual redox additive to bolster the energy storage properties of the asymmetric NPCSs-GS//BPCS-GS supercapacitor. The fabricated asymmetric supercapacitor, enhanced with AQSA/KI, not only exhibited a remarkable energy density of 86.3 Whkg⁻¹ at a desirable power density of 340 Wkg⁻¹ but also demonstrated excellent cyclic stability (with only a 22% capacity retention loss after 5000 consecutive charge-discharge cycles). These favorable electrochemical characteristics, coupled with outstanding supercapacitive performance, make this prepared asymmetric device highly suitable for practical applications. In the second study, highly porous nitrogen-doped carbon spheres (NPCS) were directly grown onto graphene sheet surfaces using a hydrothermal method combined with chemical activation. The energy storage performance of the NPCS-GS positive electrode was subsequently enhanced by leveraging the role of hydroquinone sulfonic acid (HQSA) within the cathodic electrolyte and as an electrode active material. Specifically, the surface of the carbon spheres was directly coated with polypyrrole (PPY), where HQSA served a dual function as both a polymer counter-anion and a cathodic redox additive. The NPCS-GS electrode was also employed as the negative electrode in the construction of an asymmetric supercapacitor. The electrochemical performance of this negative electrode was significantly improved by adding alizarin red S (ARS) as an anodic redox additive. Ultimately, the energy density of the fabricated PPY(HQSA)@NPCS-GS//NPCS-GS asymmetric supercapacitor was notably enhanced due to the simultaneous introduction of HQSA and ARS into the acidic electrolyte. Indeed, this research involved the engineering of electrode active material structures along with the utilization of an efficient dual redox electrolyte. This synergy resulted in an asymmetric supercapacitor exhibiting exceptional electrochemical energy storage performance, characterized by a wide potential window of 1.8 V, a desirable energy density of 60.37 Whkg⁻¹, and a suitable power density of 0.63 kWkg⁻¹. Furthermore, this supercapacitor device retained approximately 80% of its initial capacity after 5000 consecutive charge-discharge cycles at a current density of 3.5 Ag⁻¹. Therefore, this supercapacitor, with its impressive energy density coupled with outstanding features like optimal power density and high cyclic lifespan, is perfectly suited for applications in next-generation energy storage technologies. In the third study, the simultaneous presence of metal oxides in the electrode structure and redox additives in the electrolyte was leveraged to further enhance the energy storage performance of a supercapacitor. In this research, carbon felt was utilized as a high-performance, flexible substrate. Carbon spheres were directly grown onto this carbon substrate, followed by chemical activation with zinc chloride to increase their surface area. Subsequently, a V₃O₇ structure, capable of sodium ion intercalation and de-intercalation, was hydrothermally grown onto these carbon structures to create a high-performance supercapacitor electrode. Finally, a flexible asymmetric supercapacitor was constructed using the V₃O₇@PCS-CF as the positive electrode and PCS-CF as the negative electrode. A gel electrolyte based on Na₂SO₄, with the addition of dihydroxybenzoic acid as a cathodic redox additive and neutral red as an anodic redox additive, was employed in this flexible supercapacitor. This flexible asymmetric supercapacitor, designated V₃O₇@PCS-CF//PCS-CF, exhibited a high energy density of 95.7 Whkg⁻¹ alongside a desirable power density of 0.91 kWkg⁻¹ and a wide potential window of 2.2 V. Furthermore, the device maintained approximately 74% of its initial capacity after 5000 charge-discharge cycles at a current density of 7 Ag⁻¹
  9. Keywords:
  10. Asymmetric Supercapacitor ; Biomass ; Porous Carbon Materials ; Redox Electrolyte ; Flexible Supercapacitor

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